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- Tuning Exchange 2003
- Deprecated Exchange 2000 Tuning Parameters
- Exchange 2003 Tuning Parameters
- Exchange 2003 Tools
- Resources and Links
- Summary
Exchange 2003 Tuning Parameters
Now that we have gone over the legacy tuning parameters from Exchange 2000 that need to be removed, let's dive into the new tuning parameters in Exchange 2003. Some of these parameters (e.g., the BOOT.INI switches, the OWA spell-check throttling, and so on) have been mentioned in previous chapters, so those won't be duplicated here. I have listed the Exchange 2003 tuning parameters in the following subsections.
Outlook Web Access Parameters
OWA is highly configurable. We've discussed in earlier chapters some features (such as themes and spell-check management) that demonstrate this. You can also configure or enable other settings that provide even more control over the OWA experience, such as attachment blocking, access to freedocs, control over the OWA cookie timeout, enhanced segmentation, and more.
Attachment Blocking
As part of Microsoft's Trustworthy Computing initiative, Exchange 2003 OWA automatically blocks attachments with certain extensions. OWA prevents the sending and opening of a superset of attachments and MIME types using a two-level blocking mechanism. Level 1 items are totally blocked. Level 2 items can be accessed, but only if first saved locally. The list of blocked Level 1 and Level 2 file extensions and blocked MIME types are configured through four registry entries, which are listed in the following registry entries showing their default values. As you can see, many of the default Level 1 entries for file extensions and MIME types are also default Level 2 entries. When the same entry is present for both levels, Level 1 takes precedence, and the attachment is blocked. You are free to edit any of these entries to suit your organization's specific needs. If you reinstall or update Exchange, your changes will remain.
Location: HKLM\System\CurrentControlSet\Services\MSExchangeWeb\OWA Value: Level1FileTypes Type: REG_SZ Value Data: ade,adp,app,asx,bas,bat,chm,cmd,com,cpl,crt,csh,exe,fxp,hlp,hta, inf,ins,isp,js,jse,ksh,lnk,mda,mdb,mde,mdt,mdw,mdz,msc,msi,msp, mst,ops,pcd,pif,prf,prg,reg,scf,scr,sct,shb,shs,url,vb,vbe,vbs, wsc,wsf,wsh Location: HKLM\System\CurrentControlSet\Services\MSExchangeWeb\OWA Value: Level1MIMETypes Type: REG_SZ Value Data: application/hta,x-internet-signup, application/javascript,application/x-javascript, text/javascript,application/msaccess,application/prg, text/scriptlet Location: HKLM\System\CurrentControlSet\Services\MSExchangeWeb\OWA Value: Level2FileTypes Type: REG_SZ Value Data: ade,adp,asx,bas,bat,chm,cmd,com,cpl,crt,exe,hlp,hta,htm,html,htc, inf,ins,isp,js,jse,lnk,mda,mdb,mde,mdz,mht,mhtml,msc,msi,msp,mst, pcd,pif,prf,reg,scf,scr,sct,shb,shs,shtm,shtml,stm,url,vb,vbe,vbs, wsc,wsf,wsh,xml,dir,dcr,plg,spl,swf Location: HKLM\System\CurrentControlSet\Services\MSExchangeWeb\OWA Value: Level2MIMETypes Type: REG_SZ Value Data: text/xml,application/xml,application/hta,text/html, application/octet-stream,application/x-shockwave-flash, application/futuresplash,application/x-director
In addition to this level of attachment blocking, OWA 2003 enables you to selectively block attachments for users based on how they are accessing OWA. For example, for security, bandwidth, or other reasons, you might wish to block attachments for users who access OWA from the Internet (e.g., via a front-end server) while allowing full access to attachments for users accessing OWA from your private network (e.g., directly via the back-end server). To do this, you need to add the following new entry to the registry(ies) of your OWA server(s).
Location: HKLM\System\CurrentControlSet\Services\MSExchangeWeb\OWA Value: DisableAttachments Type: REG_DWORD Value Data: 0, 1, or 2 (dec)
If DisableAttachments is not present or is set to 0, the standard Level 1/Level 2 attachment blocking is performed. When DisableAttachments is set to 1, all attachments are blocked. If you set DisableAttachments to 2, attachments not blocked by Level 1/Level 2 blocking are allowed on back-end servers but not on front-end servers.
While you may not have heard of freedocs, chances are you have used them before. If you have ever dragged and dropped a document or a file directly into an Exchange folder (as opposed to attaching it to a message or post), you have used freedocs. Freedocs is the term given to stand-alone data in the information store. Because the dropped file is not an attachment of a message, it is considered a "free document" or a freedoc.
Freedocs are not new to Exchange 2003; they were present in all prior versions of Exchange. For example, in Exchange 2000, freedocs became accessible via OWA URLs (e.g., http://ex2k3/public/training/exchange2003/intro_to_e2k3.doc). What is new to Exchange 2003 (as part of Secure by Default) is the ability to control access to freedocs through these OWA URLs. Here is a registry entry you can add to your OWA servers to control access.
Location: HKLM\System\CurrentControlSet\Services\MSExchangeWeb\OWA Value: EnableFreedocs Type: REG_DWORD Value: 0, 1, 2, or 3 (dec)
If EnableFreedocs is not present or is set to 0, freedocs are completely blocked in OWA. Because the value is not present by default, freedocs are blocked out-of-the-box in OWA. When EnableFreedocs is set to 1, freedocs are accessible only when accessed directly via a back-end server; freedocs will not be accessible to OWA users connecting through a front-end server. If you set the value to 2, freedocs will be accessible from back-end servers and from any front-end server configured with a Host Header entry that matches the following registry on the back-end server.
Location: HKLM\System\CurrentControlSet\Services\MSExchangeWeb\OWA Value: AcceptedAttachmentFrontEnds Type: REG_SZ Value: comma-delimited list of FE servers, e.g., www.something.com,www.somethingelse.com
Finally, when EnableFreedocs is set to 3, freedocs are accessible to all OWA users.
OWA Cookie Timeout
In Chapter 5, I described FBA, which makes using OWA more secure. FBA uses cookies authentication; that is, it stores the user credentials in a cookie that expires after a predetermined amount of time. In Chapter 6, I detailed the default session inactivity timeout settings for trusted (private) computers and shared (public) computers (the TrustedClientTimeout and PublicClientTimeout settings). In addition to idle timeouts, you can also specify a timeout value for the FBA cookie. To do this, add the following registry entry to the OWA server.
Location: HKLM\System\CurrentControlSet\Services\MSExchangeWeb\OWA Value: KeyInterval Type: REG_DWORD Value Data: Timeout value (in minutes)
You can set KeyInterval to any value between 1 and 1440 (between 1 minute and 24 hours). If you add this registry entry, you will need to stop and restart the World Wide Web Publishing Service for the change to take effect.
Enhanced Segmentation
Exchange 2000 Service Pack 2 introduced a new feature called OWA segmentation. OWA segmentation, which is described in Microsoft Knowledge Base article 311154 (among other places), enables administrators to selectively enable and disable specific OWA features. OWA can be segmented or a per-user or per-server basis, with user settings taking precedence over server settings. There are a variety of reasons to segment OWA; for example, some organizations do not want users to have access to all OWA features because of security reasons or training concerns. Monetary reasons also exist—application service providers that sell hosted Exchange services may want to segment OWA and sell both a lite version and a full-featured version of OWA. This is sometimes referred to as tiered licensing or provisioning.
Per-server segmentation is performed by adding a specific hexadecimal value to the registry of the mailbox server, as shown here.
Location: HKLM\System\CurrentControlSet\Services\MSExchangeWeb\OWA Value: DefaultMailboxFolderSet Type: REG_DWORD Value Data: See Table 10.1
Per-user segmentation is performed by configuring the msExchMailboxFolderSet attribute in Active Directory. This is an attribute of all mailbox-enabled users. In Exchange 2000, this attribute did not exist prior to Service Pack 2. To segment OWA you had to manually extend the Active Directory schema using OWASCHEMA.VBS, which added this attribute. Because this was a manual process, it is possible that your Exchange 2000 forest does not contain this attribute. However, as soon as Exchange 2003 FORESTPREP is performed, this attribute will be added.
Both DefaultMailboxFolderSet and msExchMailboxFolderSet are decimal values based on the bit masks shown in Table 10-1. Each bit mask corresponds to an individual OWA feature. Create a list of the features you want to enable, and add together their bit mask values. Then enter this sum as the decimal value in the registry or in Active Directory. Many of these values existed in Exchange 2000 Service Pack 2 and later; values that are new to Exchange 2003 have a checkmark in the New to Exchange 2003 column.
Once you have added all of the hex values, enter the sum in the appropriate place. For example, if you want to enable access to only the Messaging and Calendar features, you would use the following formula:
+ 0x00000002
You would then enter 0x00000003 in the registry or in Active Directory, depending on where you want to configure this.
Table 10-1. OWA Segmentation Values
Exchange Feature
Bit Mask Value (Hex)
New to Exchange 2003
All Features
Junk E-mail
New Mail
Public Folders
Rich Client
Search Folders
Spell Check
Enabling Public Folder Replies
By design, unless you are accessing OWA through a front-end server (and not directly via a back-end server), you will not be able to use the Reply, Reply All, or Forward functions for messages contained in public folders. While you'll be able to reply to and forward all messages in your mailbox regardless of how you access OWA, unless you go through an Exchange 2003 front-end server, you will not be able to take these actions for public folder messages.
In addition to these restrictions, by default there is a 2MB limit for all messages sent via a reply or forward action. You can override this limit by adding the following registry entry to your front-end servers, which specifies the allowable maximum size.
Location: HKLM\System\CurrentControlSet\Services\MSExchange\OWA Value: maxPFReplyForwardSize Type: REG_DWORD Value Data: X
For the maxPFReplyForwardSize entry, X is the maximum size you want to set in kilobytes.
Outlook Parameters
In previous chapters, I wrote about the new features in Outlook 2003 specifically targeted at Exchange users. Features such as RPC over HTTP (which is really RPC over HTTPS), Cached Exchange Mode, and others help to greatly improve the overall experience for Outlook users. In addition to these new features, a variety of administrative options can be set to improve the experience for both Outlook users and Exchange administrators, such as improved alias matching, the ability to disable MAPI compression, control of RPC over HTTPS polling, and improved behavior regarding the ability to restrict access to Exchange based on the version of Outlook that is running.
Alias Matching
If you enter an alias into the TO, CC, or BCC fields in Outlook, before the message can be sent the recipients must first be resolved. Outlook would look up the information in the Global Address List and/or in a personal address book or in Outlook contacts. By default, any partial name that you enter is checked against three naming fields: first name, last name, and alias. Consider the following entries in the Global Address List.
First Name Last Name Alias John Doe JohnD Johnny Roe JohnR
If you enter "John" on any of the address field lines, Outlook will match both entries and ask you to choose which entry to use. Previous versions of Outlook enabled you to bypass duplicate entries by appending an equals sign (=) to the beginning of your entry. For example, to bypass duplicate entries and specify Johnny Roe, you would enter "=JohnR" into the address field. Because Johnny Roe's alias is JohnR, it is instantly matched.
Outlook 2003 improves this behavior by eliminating the need to use the equals sign if you have added the following Outlook registry setting.
Location: HKLM\Software\Microsoft\Exchange\Exchange Provider Value: OAB Exact Alias Match Type: REG_DWORD Value Data: 1 (dec)
If the OAB Exact Alias Match value is not present or is set to anything other than 1, Outlook 2003 will behave like all other Outlook clients and will exactly match an alias only when the equals sign is used. If the value is present and set to 1, Outlook will resolve the exact alias without providing a list of possible matches.
MAPI Compression Settings
In Chapter 2, I wrote about a new feature called MAPI compression (referred to internally as AirMAPI) that is available when you use Outlook 2003 and Exchange 2003 together. AirMAPI compresses all content at the Exchange server before sending it to Outlook, which decompresses it. When AirMAPI is enabled, another feature called Buffer Packing is also enabled. With Buffer Packing, information sent from Exchange to Outlook is packaged in bigger, optimized buffer packets, which reduces the number of packets that ultimately need to be sent.
While AirMAPI and Buffer Packing provide some impressive performance improvements, they can hinder some troubleshooting efforts. When troubleshooting client-server issues, a common practice is to use a network sniffer such as Network Monitor to capture network traffic for analysis. Because AirMAPI is enabled by default, it can make troubleshooting more difficult because all of the data in the trace is compressed and therefore not readily discernable. Fortunately, you can use the following server-side registry entries to control and/or disable AirMAPI and Buffer Packing if needed.
Location: HKLM\System\CurrentControlSet\Services\MSExchangeIS\ParametersSystem Value: Rpc Compression Enabled Type: REG_DWORD Value Data: 0 or 1 Location: HKLM\System\CurrentControlSet\Services\MSExchangeIS\ParametersSystem Value: Rpc Compression Minimum Size Type: REG_DWORD Value Data: X Location: HKLM\System\CurrentControlSet\Services\MSExchangeIS\ParametersSystem Value: Rpc Packing Enabled Type: REG_DWORD Value Data: 0
None of these entries exist by default, and therefore they need to be manually added if you want to configure or disable AirMAPI. If Rpc Compression Enabled is not present or is set to 1, AirMAPI compression is enabled. Any other value will disable it. The Rpc Compression Minimum Size entry is used to specify a minimum size for an RPC packet in order for AirMAPI to be used. If this value is not present, a default value of 1,024 bytes is used. In this example, X represents the desired minimum size in bytes.
Finally, you can selectively enable and disable Buffer Packing by using the Rpc Packing Enabled entry. If this entry is not present, a value of 1 is assumed and Buffer Packing is enabled. When this entry is set to 0, Buffer Packing is disabled.
When changing any of these settings, you will need to stop and restart the Information Store service for the change(s) to take effect. Because of the benefits provided by AirMAPI and Buffer Packing, I recommend disabling these features for troubleshooting purposes only.
RPC over HTTPS Polling
When making an initial connection to an Exchange server, Outlook registers itself for new message notifications. Whenever a new message is received in an Outlook user's mailbox, Exchange sends a notification to Outlook using UDP. This notification is essentially a small flag to the client that a new message is present and needs to be displayed. When Outlook receives the UDP notification, it retrieves the message from the Exchange server and displays it in the appropriate folder (e.g., the Inbox).
New message notifications are intended for Outlook clients that are running in either online mode or Cached Exchange Mode, and they won't work for Outlook clients using RPC over HTTPS. In fact, when using RPC over HTTPS, Outlook does not register for notifications (because it won't be able to receive them). Instead, Outlook clients using RPC over HTTPS use a polling mechanism to check for new messages. While polling is initiated by Outlook, the polling frequency is dictated by the Exchange server. Polling is not new to Outlook 2003; Outlook 2002 automatically reverts to polling if the UDP notification fails. However, new in Exchange 2003 is your ability to configure a polling interval for RPC over HTTPS clients.
By default, Outlook 2003 will poll every 60 seconds. You can change the frequency by adding the following registry entry to the Exchange server that contains the user's mailbox.
Location: HKLM\System\CurrentControlSet\Services\MSExchangeIS\ParametersSystem Value: Maximum Polling Frequency Type: REG_DWORD Value Data: X
For this value, X is the minimum number of milliseconds between polling intervals. If Maximum Polling Frequency is not present, a default value of 60 seconds (60000 when set in milliseconds) is used. Again, this is the minimum number of milliseconds between polling intervals, which means that polling does not take place every 60 seconds. Instead, polling will occur any time between the polling frequency interval and twice that interval. For example, if you set Maximum Polling Frequency to 90 seconds, polling will take place between 90 and 180 seconds after the last poll.
When configuring this value, keep in mind the following important information. First, Microsoft does not recommend lowering this value because of the performance hit to Exchange, Outlook, and the network. Therefore, you should not use a polling frequency less than 60 seconds. Second, you may not need to adjust polling at all because many user actions will actually check for the new message flag as part of internal operations. For example, if you switch folders or open a message, new items on the server will be displayed. This occurs because when Outlook sends necessary RPC requests to Exchange to effect the user action, the new message flag is checked and, if present, the new message notification is included in the RPC response sent back to Outlook.
Outlook Version Blocking
Both Exchange 2000 and Exchange 2003 support a feature that enables administrators to prevent specific versions of MAPI clients from connecting to and using Exchange. For example, if you want to allow only Outlook 2003 users to connect to your Exchange server, you would configure the registry on the Exchange server as described in Microsoft Knowledge Base article 288894. You can also use this feature to disable all MAPI access to an Exchange server (by specifically blocking all known MAPI clients) or to block unpatched versions of Outlook 2003 (or any other Outlook client) from using Exchange until they have all required updates.
After adding the appropriate settings to the registry, Exchange 2000 required you to stop and restart the Information Store service for the change to take effect. New in Exchange 2003 is the ability to dynamically read this value from the registry and apply it without having to restart the store. A background thread checks this value every 15 minutes, so the most you'll ever need to wait for this change to take effect is 15 minutes. Because the 15-minute cycle for the background thread is hard-coded, if you want the change to take effect sooner, you still need to cycle the Information Store service.
Exchange Server Parameters
On an Exchange 2003 server you can configure a few additional parameters that provide you with additional levels of control. Some of these parameters have already been discussed in other chapters, such as the Recovery SG Override setting described in Chapter 8 and the OWA spell-check throttles described in Chapter 9. The additional parameters enable you to control out-of-office messages (OOFs)2 and delivery status notification (DSN) messages, reenable the M: drive, and designate a specific system for backfilling public folders.
Controlling Out-of-Office Messages
When an Outlook user enables the Out of Office Assistant to generate OOFs, an OOF is generated for messages sent to this user when his or her e-mail address is explicitly listed in the TO or CC fields or when he or she is a member of a distribution list (or mailing list) listed in the BCC field. For a variety of reasons, you may wish to limit OOFs to those cases where a user is specifically listed in the TO or CC fields and not in a BCC field. This feature is particularly useful in situations where users are members of mailing lists managed by foreign (i.e., non-Exchange) messaging systems.
To suppress the generation of OOFs for BCC'd distribution lists, add the following registry entry to the Exchange server that contains the mailbox(es) you want to affect.
Location: HKLM\System\CurrentControlSet\Services\MSExchangeIS\ParametersSystem Value: SuppressOOFsToDistributionLists Type: REG_DWORD Value Data: 1
If the SuppressOOFsToDistributionLists value is not present or is set to anything other than 1, the behavior will remain unchanged. However, when set to 1, this registry entry will suppress OOFs for BCC'd distribution lists. When you use this feature, keep in mind that an OOF will still be sent in cases where a message is sent to an individual recipient using the BCC field only (i.e., no recipients in TO or CC fields) even if SuppressOOFsToDistributionLists is enabled. This applies only if the recipient is in the BCC field and the TO and CC fields are blank. If another recipient is present in the TO or CC fields, SuppressOOFsToDistributionLists will suppress the OOF.
Controlling Delivery Status Notifications
When an Exchange user sends a message to an external recipient whose messaging system is configured to use custom nondelivery reports (NDRs), the user may not receive the custom NDR and instead may receive a standard NDR similar to the following one.
From: System Administrator To: <sender name> Subject: Undeliverable: <subject> Your message did not reach some or all of the intended recipients. Subject: <subject> Sent: <date> <time> The following recipient(s) could not be reached: <recipient> <date> <time> The e-mail account does not exist at the organization this message was sent to. Check the e-mail address, or contact the recipient directly to find out the correct address. <Domainname #5.1.1>
A standard NDR is received instead of the foreign system's custom NDR because the Exchange information store reformats the message as the message is converted to a MAPI message. When this happens, any customizations made to the NDR are lost. (Note though that this happens only with MAPI clients; if you access the message using a non-MAPI client instead, the custom NDR will be preserved.)
In Exchange 5.5 and earlier versions, the custom NDR was also preserved even when viewed by a MAPI client. Exchange 2000 added support for the Report content type as prescribed in RFC 1892, and this effectively broke custom NDRs. Based on feedback from its customers, Microsoft allowed this behavior to be modified by using a registry entry on the Exchange server for customers running Exchange 2000 Service Pack 3 plus the hotfix from Microsoft Knowledge Base article 812806 or later. The code changes in the hotfix have been rolled into Exchange 2003, enabling you to add the following registry entry to your Exchange server to override the conversion behavior and render the NDRs as intended by the foreign mail system.
Location: HKLM\System\CurrentControlSet\Services\MSExchangeIS\ParametersSystemInternetContent Value: RenderDSNsAsMessages Type: REG_DWORD Value Data: 1
If RenderDSNsAsMessages is not present or is set to anything other than 1, the custom NDR will not be preserved. If the registry entry is set to 1, the custom NDR is preserved and viewable by MAPI clients. This change takes effect dynamically so there is no need to restart the server or any services.
Reenabling the M: Drive
As I wrote in Chapter 3, Exchange 2000 shipped with a feature known as the Exchange Installable File System (ExIFS, often simply called IFS). ExIFS is a kernel-level driver that exposes some of the data from the Exchange information stores to the Windows file system through a drive letter mapping. By default, the drive letter used was M. If this letter was already in use for a drive mapping, the next available letter was used (e.g., N, O, and so on). The ExIFS drive mapping was not the same as a local or network drive, although it was widely misinterpreted as one. Many administrators treated the M: drive like a physical disk; some administrators scanned the drive with antivirus scanners or took backups of it, mistakenly believing they were backing up their Exchange data. Others set permissions on Exchange items through the file system. Unfortunately, these actions were not supported, and in most cases they actually damaged the information store databases.
Remember, the whole idea of product evolution is to design and evolve the product in a way that keeps support calls to an absolute minimum. With ExIFS, the exact opposite was happening; administrators with damaged databases posted frantic requests for help in Microsoft's newsgroups, while at the same time PSS was receiving a high volume of calls on this same issue. To address this problem, and more importantly to prevent it from happening again with Exchange 2003, Microsoft changed the default behavior for ExIFS and left it turned off. Whether you upgrade from Exchange 2000 or install a fresh copy of Exchange 2003, the drive mapping for ExIFS will not be present unless and until you enable it.
From a best-practice perspective, you should not enable the ExIFS drive mapping unless you have a very specific reason you need to do this. If you do reenable the M: drive (regardless of what drive letter is actually assigned), you should be aware of the following caveats.
Only non-MAPI content should be accessed via this drive. Accessing MAPI data via ExIFS is not supported and could damage your store.
You should not share out the M: drive or any folders under this drive. In other words, do not create a Windows file share for SMB-based access. If you need to expose the non-MAPI data to network users, you can use Web Folders instead.
If you enable the drive mapping, you will need to reboot Exchange every time you install an update or an upgrade (e.g., a new service pack).
The same restrictions in Exchange 2000 still apply. Do not scan the M: drive; do not use backup software to back up the M: drive; and do not set any ACLs or other permissions on the M: drive.
If after reading this far you still want to reenable the M: drive, you can do so by adding the following registry entry to your Exchange server.
Location: HKLM\System\CurrentControlSet\Services\ExIFS\Parameters Value: DriveLetter Type: REG_SZ Value Data: M
If you prefer to use something other than M for the drive letter, simply enter the desired letter for the value data. You will then need to reboot the Exchange Information Store service for this setting to take effect. Also, if you decide to later disable this drive mapping, simply removing the registry entry and cycling the information store may not be sufficient. You may also need to use the procedure documented in Microsoft Knowledge Base article 305145.
Backfilling the Public Folder
Whenever any update is made to an Exchange public folder, a change number (CN) is assigned to the folder, which is used by the replication engine to track folder updates. A set of CNs is called a CNSet. Whenever one Exchange server sends updates to another Exchange server, it includes its CNs. The receiving server reads the sending server's CNs to determine whether any changes have been made and whether the receiving server is missing any data as a result of the change(s). If it is missing data, backfilling will occur.
Backfilling provides a recovery mechanism in a variety of situations, such as when a public store has been restored from a backup or has been offline for some time, or when replication messages are somehow lost in transit. If a public folder store detects a gap in any folder's CNSet, it issues a Backfill Request message. The server to whom the request is sent responds with a Backfill Response message that includes the missing data.
A new feature in Exchange 2003 is a setting that provides you with the ability to override the default public folder backfill algorithm and designate a preferred server for backfill requests. This setting can be implemented as an Active Directory attribute or as a registry setting on the Exchange server. Before an Exchange server sends a backfill request, the Active Directory attribute is checked first. If the attribute is null, the registry is checked. If the entry is not present, the default algorithm for public folder backfilling is used.
If you want to use the Active Directory attribute, enter the GUID of the desired backfill server to the msExchPreferredBackfillSource attribute on the Exchange server's public information store object (e.g., on the server sending the Backfill Request message, not on the one you want to use as the backfill server). If you prefer using the registry, add the following entry on the server sending the Backfill Request message.
Location: HKLM\System\CurrentControlSet\Services\MSExchangeIS Value: Preferred Backfill Source Type: REG_SZ Value Data: Public Folder Store GUID of desired backfill server
Both the Active Directory attribute and the registry change take effect dynamically (they are checked as part of each backfill request), so there is no need to stop or start anything.


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Larynx during exercise: the unexplored bottleneck of the airways
- 2.3k Downloads
- Citations
Exercise-induced shortness of breath is not uncommon in otherwise healthy young people. Based on the presenting symptoms alone, it is challenging to distinguish exercise-induced asthma (EIA) from exercise-induced obstruction of central airways, sometimes leading to diagnostic errors and inadequate treatment. Central airway obstruction usually presents with exercise-induced inspiratory symptoms (EIIS) during ongoing exercise. EIIS tends to peak towards the end of an exercise session or immediately after its completion, contradicting symptoms of EIA typically peaking 3–15 min after the exercise has stopped. EIIS is usually associated with some form of laryngeal obstruction. Transnasal flexible laryngoscopy performed continuously throughout an incremental exercise test from rest to exhaustion or to intolerable symptoms is usually diagnostic, and also provides information that is important for further handling and treatment. Reflecting the complex anatomy and functional features of the larynx, exercise-induced laryngeal obstruction (EILO) appears to be a heterogeneous condition. Contradicting previous beliefs, recent literature suggests that laryngeal adduction in a majority of cases starts in supraglottic structures and that vocal cord adduction (VCD) most often occurs as a secondary phenomenon. However, EILO is poorly understood and more and better research is needed to unravel causal mechanisms. The evidence base for treatment of EILO is weak. Speech therapy, psychotherapy, biofeedback, muscle training, anticholinergic aerosols have all been applied, as has laser supraglottoplasty. Randomized controlled trials with well-defined and verifiable inclusion and success criteria are required to establish evidence-based treatment schemes.
KeywordsLarynx Exercise capacity Exercise-induced asthma Exercise-induced laryngeal obstruction Vocal cord dysfunction Exercise testing Respiratory measurement
- CLE test
Continuous laryngoscopy exercise test
Exercise-induced asthma
Exercise-induced inspiratory symptoms
Exercise-induced laryngeal obstruction
The ratio between forced expiratory flow at 50 % of forced expiratory vital capacity and the forced inspiratory flow at 50 % of forced inspiratory vital capacity
Forced expiratory flow in the first second
Flow volume loop
Gastroesophageal reflux disease
Inspiratory muscle strength training
Laryngopharyngeal reflux
The ratio between maximal inspiratory flow at 50 % of forced inspiratory vital capacity and the maximal expiratory flow at 50 % of forced expiratory vital capacity
- PCA-muscle
Posterior cricoarytenoideus muscle
Pulmonary function test
Proton pump inhibitor
Paradoxical vocal cord motion
Reflux symptom index
Vocal cord dysfunction
Ideally, ventilation should not limit exercise capacity in young and otherwise healthy individuals [1]. However, various forms of airway obstruction do occur, increasing the work of breathing and producing exercise-induced respiratory symptoms. Thus, exercise-induced shortness of breath is not uncommon, and a scenario most physicians must be prepared to encounter. Principally, airway obstruction inside the thoracic cage produces expiratory symptoms (as in asthma), while obstruction outside the thoracic cage produces inspiratory symptoms. The purpose of this article is to provide state-of-the-art knowledge on diagnostics and treatment modalities of central airway obstruction in patients presenting with exercise-induced inspiratory symptoms (EIIS). The article focuses primarily on the role played by the larynx, representing the "entrance valve" and the narrowest passage of the airway tree.
Authors have related EIIS to distinct diagnoses, conditions or dysfunctionalities in specific structures, most often the vocal folds. Hence, the term vocal cord dysfunction (VCD) has become widely used. However, the proposal that the vocal folds are causally involved in EIIS is based on weak evidence and often not verified by objective methods [2, 3]. A plethora of diagnostic terms has been used in the literature to label relatively similar clinical entities, and vice versa, similar labels are given to conditions that may very well represent different diseases [4]. There is no agreement on important issues like diagnostic work-up, etiology, and treatment. This unfortunate situation may be related to heterogeneities within the patient populations, so far not properly acknowledged. Thus, patients presenting symptoms in different situations (e.g., exercise vs. non exercise) have been lumped together in studies, somehow assuming a similar etiology [5]. Moreover, patients referred to third level specialized otorhinolaryngology clinics most certainly differ from patients seen at clinics dealing mainly with respiratory diseases. As research groups will interpret symptoms and findings within the context of their own experience and expertise, there may in fact be no genuine disagreements, only genuine attempts to interpret a heterogeneous reality.
We searched PubMed for "exercise" combined with: vocal cord dysfunction, paradoxical vocal fold motion, laryngomalacia, laryngeal obstruction, and laryngeal dysfunction. The search was quality checked by scrutinizing the reference lists of included studies. Systematic assessment of relevance, design and quality was complicated by large variations (or lack of statements) regarding diagnostic methods, patient inclusion, evaluation and treatment. Particularly, studies tended to mix patients with exercised-induced symptoms and those with symptoms presenting primarily at rest, two conditions that are likely to represent different disease domains. Stating clearly in the text when doing so, we have allowed ourselves to express personal opinions, based on articles published by our group and a cumulative experience from more than 700 patients with EIIS, examined endoscopically during exercise in the past 15 years. Thus, the article does not fully comply with all requirements for a systematic review, and is biased by the authors' experience and access to large numbers of high-quality videos of patients presenting with EIIS, suffering from EILO [6].
Diagnosing EILO
Exercise-induced inspiratory stridor is often confused with symptoms of exercise-induced asthma (EIA) [7, 8]. The prevalence of EIA has been estimated to 8–10 % in unselected childhood populations and approximately 35 % in children with untreated asthma [9]. The incidence of EILO was reported to be as high as 7.5 % in unselected young people in Copenhagen [10]. Treatment with asthma medication is common in patients with EIIS, often with little or no effect [11, 12]. In our own study [13], 85 % of patients with EIIS had received asthma treatment prior to being diagnosed with EILO, with no effect on exercise-related symptoms in 64 %. However, it is important to bear in mind that EIA and EILO may coexist [2, 3, 11, 12, 14].
Three main criteria have been proposed as essential to the diagnosis EILO): (1) Clinical symptoms of EIIS. (2) Confirmatory pulmonary function findings and (3) Laryngeal obstruction, verified laryngoscopically [2, 3, 15, 16, 17, 18].
Clinical symptoms
Patients are often unable to account for their symptoms in detail at first visit, but rather present with some form of respiratory complaints occurring during exercise, often made worse by cold climate and also not responding as expected to asthma medication. Two key questions should be answered regarding symptoms: their position in the respiratory cycle (inspiratory vs. expiratory) and in the exercise session (during or immediately after vs. 10–15 min after). If properly informed, most patients are able to respond to these questions if rescheduled a week or two later.
In a test situation, EIA is characterized by changes in forced expiratory volume in first second (FEV1) occurring from before vs. after the exercise session [19]. The symptoms occur as a response to exercise; i.e., slowly evolving during the first 3–15 min after stopping and mainly involving the expiratory part of the respiratory cycle [20]. A correctly performed test for exercise-induced asthma is of diagnostic value also with respect to EIIS, as inspiratory symptoms should be revealed by the high-intensity exercise—if present. Breath patterns and symptoms during the test must be recorded, not only changes in FEV1 after exercise. EIIS is usually characterized by a fairly typical pattern, starting with increasing breathing difficulties accompanied by a prolonged inspirium with course or high-pitched or stridor-like inspiratory breaths sounds, sometimes progressing to clear-cut stridor, hyperventilation attacks or frank panic reactions, evolving in parallel to the increasing ventilatory requirements [15, 21]. Pain reactions located to the chest or throat area are relatively common (unpublished own data). It is important in this context to remember that EIIS is not a well-defined entity, but rather a series of symptoms that usually occur in sequence, somewhat open to subjective interpretation. A thorough description of observations made during an exercise test should serve to differentiate symptoms of asthma from EIIS.
Pulmonary function tests
Several studies have described abnormal resting flow-volume loops (FVL) in patients with EIIS [2, 3, 7, 22]. According to Christopher [15] the most common cause of blunted or truncated inspiratory FVL is inadequate instruction, suboptimal effort or inability to perform the procedure. The repeatability of the findings is poor [23, 24] and the sensitivity regarding identification of patients with EIIS is low [2, 3, 25, 26]. Various cut-off levels for inspiratory vs. expiratory flow ratios have been suggested, with no validated consensus obtained [3, 22, 25, 27].
In summary, there is currently no evidence to suggest that EILO can be confirmed or rejected by resting pulmonary function tests (PFT) alone, and to use exclusively FVLs to set specific intrinsic laryngeal diagnoses such as VCD seems futile. Nevertheless, PFTs are important, partly to distinguish asthma from EIIS but also to indicate the presence of structural central airway obstructions such as subglottic stenosis, laryngo-tracheo-bronchomalacia or intrathoracic compressions of various forms. Distinct and reproducible flatting of the inspiratory and/or expiratory parts of the FVL in patients with EIIS should incite further assessment [15].
Laryngoscopic visualization
Visualization of laryngeal structures during exercise has been proposed the "gold standard" for diagnosing EILO [2, 3, 15, 17, 18, 28, 29, 30]. Christopher showed in a review of 355 articles on VCD that laryngoscopy during ongoing symptoms had not been performed in 38 % of patients [15]. Newman wrote that laryngoscopy was diagnostic in only 60 % of symptomatic patients [12]. There are several possible explanations for this lack of findings. Importantly, symptoms resembling EIIS may be unrelated to larynx in an unknown proportion of patients, since obstruction of trachea or main bronchi can produce symptoms difficult to distinguish from those of EILO [13]. Second, in most studies laryngoscopies were performed post-exercise, which is a questionable method. EIIS usually peaks at maximum ventilation and often resolves rapidly thereafter. As the minute ventilation falls rapidly after stopping of exercise [1], the time required to introduce a laryngoscope in a distressed patient may result in false-negative tests. Alternatively, the test situation may be inadequate in that patients are unable to exercise to the level necessary to reproduce their symptoms. A final issue is lack of consensus regarding what are normal and what are abnormal findings.
Continuous laryngoscopy exercise test (CLE test)
Mode of exercise used to reproduce EIIS
Treadmill running, ergometer cycling or stair climbing have all been used to provoke and reproduce symptoms of EIIS [3, 17, 29, 31]. Ideally, the mode of exercise should be tailored to the individual patient, based on triggers identified from the medical history. In a laboratory setting, one must compromise. More important than the mode of exercise is to ensure that the exercise continues to exhaustion or intolerable symptoms. In most young people and fit adults, treadmill exercise is better than bicycle to achieve this aim [32]. Tervonen used a stationary bicycle in their study and was unable to reproduce symptoms in 50 % of patients and made laryngeal findings in only 30 % [17], demonstrating the importance of this issue.
Normal laryngeal movements during exercise
The human larynx protects the lower airways from aspiration, facilitates respiration and plays a key role in phonation. The supraglottic part, i.e., aryepiglottic fold, cuneiform tubercles and epiglottis, are supported by muscles, ligaments and membranes. Tiny fibers from the lateral belly of vocal fold muscles are stretched cranially into the aryepiglottic fold. During exercise, the larynx normally opens fully and the epiglottis rotates anteriorly towards the base of the tongue [29], stretching the aryepiglottic folds, thereby allowing for increased airflow with the least possible increase of airflow resistance [28]. Several muscles are active in this process [33]. The motion of the arytenoids occurs in three dimensions, i.e., sliding, tilting and rotation along the vertical axis. The top of each cartilage determines the position of the dorsal end of the aryepiglottic folds, whereas the anteriorly and caudally placed vocal processes determine the positions of the dorsal end of the membranous part of each vocal fold.
In the abducted position, the dorsal part of vocal folds is lifted cranially. Most of the airflow through larynx takes place in the dorsal part of the glottic aperture. The posterior cricoid muscle (PCA) acts as an abductor of the glottis; its activity synchronized and in a phasic interaction with the diaphragm muscle [33, 34, 35].
A slight adduction of the aryepiglottic folds at maximum minute ventilation was observed in 40 % of subjects without respiratory complaints participating in a study performed by our group [13] and, therefore, considered to be a normal phenomenon [36]. Bent and co-workers [29] made similar observations. Regarding the vocal gap, McFadden et al. [2] proposed that an adduction exceeding 50 % was consistent with VCD. These issues need to be addressed in larger studies. Particularly, we have no knowledge on what are normal or optimal relations between body size, ventilatory requirements and the size of the laryngeal aperture. Thus, a similar extent of adduction is likely to have different consequences in a narrow compared to a wide larynx and also for a competing athlete compared to a sedentary person.
Diversity of findings in patients with EIIS
In a study of 151 patients with EIIS using the CLE test, we observed a variety of response patterns, but the typical patient was characterized by a normal larynx at rest and moderate to severe adduction of laryngeal structures during exercise [13]. Supraglottic anteromedial motion of the aryepiglottic folds and of the cuneiform tubercles was involved in the majority of patients, and was most often the inciting event. If present, vocal fold adduction usually occurred as a secondary event or in parallel to supraglottic adduction. In some patients, a dorsal flexion of the epiglottis seemed to represent the air flow obstacle, seemingly as a primary event. Clinically, EIIS evolved in parallel to gradually increasing laryngeal obstruction. Clear-cut stridor appeared to be related to adduction of the vocal folds, and panic reactions to severe vocal fold adduction. Only four (3 %) of 151 patients had a primary glottic adduction or VCD, as defined by Christopher in 1983 [22]. Nine (6 %) subjects had a normal laryngeal response to exercise, but symptoms resembling EIIS; i.e., EIIS but no EILO. Further investigations revealed structural obstruction of central airways in seven, caused by vascular compression, tracheomalacia and subglottic stenosis. This heterogeneity of findings has been confirmed also in other and smaller studies that utilize laryngoscopy during exercise to investigate patients complaining of EIIS [10, 17, 37, 38].
After hundreds of CLE tests performed in patients with EIIS (5–65 years of age), we are unable to link EIIS to one single anatomical structure or causal factor, and certainly not exclusively to the vocal folds. Adduction of the vocal folds is not the primary event in most patients, but rather a consequence or an associated phenomenon secondary to supraglottic alterations. These findings are supported by other studies, utilizing laryngoscopy as diagnostic method [10, 39]. The anatomy, physiology, nervous regulation and function of the larynx are complex, and heterogeneities regarding exercise-induced malfunction, therefore, plausible and not surprising.
It has recently been argued that VCD may be diagnosed based on the presenting symptoms alone, and that laryngoscopy is difficult and even unnecessary [5]. This strongly contradicts the experience gathered by our group and by others, with EIIS being associated with a spectrum of structural and functional abnormalities [10, 13, 37, 38]. These distinctions are of practical importance, as patients with severe collapse of supraglottic structures benefit from laser supraglottoplasty [40, 41]. Moreover, this attitude may leave patients with EIIS due to extra-laryngeal obstruction with no (or incorrect) diagnosis.
Potential casual aspects of EILO
Aerodynamic principles
The Bernoulli principle states that increasing airflow through a tube creates increasing negative pressures within the tube [42]. Depending on airflow velocity and turbulence and the strength of the supporting structures, sooner or later the tube will yield to these forces. At what flow-rates laryngeal structures will yield is determined by the area and configuration of the laryngeal opening, "internal laryngeal solidity" and support from surrounding structures. Thus, EILO may be explained by poor support from muscles, ligaments or laryngeal cartilages.
A weakness of the PCA muscle or of the structures that stabilize the arytenoids and keep them upright and laterally positioned may be involved [35]. This will reduce the size of the laryngeal aperture, possibly to below a critical level required for laminar and advantageous aerodynamic inspiratory flow [43]. A secondary medial motion of the vocal folds may be explained by an increased negative pressure in the space between the vocal folds, due to changes of airflow induced by medial movements of the structures above [43]. This sequence would fit the observations made in most participants of our studies. It has been speculated whether there is a connection between infantile laryngomalacia and subsequent EILO. The evidence for this is relatively modest [44].
Laryngeal hyperreactivity and changes in reflex interaction
Reflexes are important for laryngeal function in relation to respiration, swallowing and protection against aspiration. The idea of "reflex associated VCD" is that direct stimulation of sensory nerve endings in the respiratory tract may induce protective reflex loops, leading to laryngeal closure [45]. Mechanical or chemical stimulation of the supraglottic mucosa or direct stimulation of the superior laryngeal nerve may activate the laryngeal adductor reflex to protect the airway from aspiration or asphyxiation [46]. A variable sensitivity and intensity of this reflex interaction could conceivably lead to a corresponding variability in the threshold for laryngeal closure. Conditions such as allergy, reflux and infections may influence these reflex interactions. So far, the evidence supporting these mechanisms is weak.
Laryngopharyngeal reflux (LPR)
Gastroesophageal reflux disease (GERD) has been associated with VCD by several authors [27, 47]. The argument has been that acidic reflux reaching the laryngopharyngeal area should induce a hyperexcitable state [27, 48]. If a causal relationship is present, one would expect that treatment with proton-pump inhibitors (PPIs) should reduce reflux symptoms as well as EIIS. In a study by Maturo et al., three patients with VCD and LPR were treated with PPI with a positive effect on LPR, but not on VCD [5]. A recent study indicated that subjects with high reflux symptom index in fact had reduced laryngeal sensitivity [49]. It is important to remember that the prevalence of GERD in unselected populations may be as high as 10–60 % [50]. Causal relationships involving conditions with this kind of prevalence should be proposed with caution.
Psychological aspects and EILO
VCD tend to be interpreted within a psychological paradigm. In their review article, Leo and Konakanchi [51] reported from a sample of 171 cases with paradoxical vocal cord motion (PVCM), and found that only 7 % did not have a psychiatric diagnosis. Others have claimed that VCD is associated with conversion disorders, representing the physical manifestation of underlying psychological problems [52]. Sexual abuse in early childhood is still being put forward, based on a small study from the 1990s [53].
In this context, it is probably important to distinguish laryngeal obstruction occurring at rest from that induced by exercise. Based on decades of personal experience working with children and adolescents with exercise-induced symptoms, we have found no reason to suspect that a majority of patients with EIIS and EILO suffer from mental disorders. It is our impression that most are otherwise healthy and physically active young people who benefit from being explained that their breathing problem is not dangerous, and that there is nothing mentally wrong with them. However, we have certainly observed that many patients are concerned and sometimes frightened by their symptoms, and therefore reluctant to expose themselves to situations they know will provoke them. In our opinion, this reaction is understandable, considering the trauma of breathlessness during heavy exercise. The panic reactions observed in some individuals should not be interpreted within a psychiatric context, but rather as a response to the choking feeling of laryngeal collapse. Post-exercise introduction of a laryngoscope in a distressed patient may simply reveal adducted vocal folds and panic, and therefore erroneously be interpreted as paradoxical vocal fold motion induced by hysteria. Thus, post-exercise laryngoscopy entails a high risk of making the classical mistake of reverse causality; the panic reaction does not cause EILO, but is caused by EILO.
As this group of patients is characterized by its heterogeneity, we do not exclude that stress, anxiety and competitive personalities may worsen and possibly also trigger symptoms and findings, but argue that an organic substrate makes the EILO response possible in most patients. This point of view is strengthened by the convincing effect of surgical treatment in selected severe cases [41].
Environmental conditions and EILO
In exercise-induced asthma, temperature and humidity are important pathogenetic factors [54, 55]. Regarding EIIS and EILO little is known. In our experience, performers of particularly winter sports, but also swimmers, handball, basket and soccer players seem to be over-represented. Most patients express that a cold climate reduces their tolerance to exercise. These findings correspond partly to the descriptions given by Rundell, reporting that inspiratory stridor was more prevalent in outdoor (8.3 %) compared to indoor athletes (2.5 %) [3], indicating that environmental factors are implicated in the pathogenesis of EILO as of EIA.
Age, gender and physical capacity in relation to EILO
EIIS seems to start in early adolescence in a majority. The design of the aryepiglottic folds and the cuneiform tubercles make the supraglottic opening relatively narrower in adolescents than in adults and the epiglottis is longer and may be curved or omega shaped [56, 57]. Relative to body size, maximum oxygen uptake peaks in adolescence, necessarily also reflected by the maximum minute ventilation. These factors may all contribute to the age distribution of EILO. Most agree that EILO is more common in girls [15, 58, 59]. Anatomical studies have shown no gender differences in the relative size of the laryngeal aperture before puberty, while there are significant gender differences throughout the pubertal growth spurt [57, 60].
Prognosis of EILO
It has been suggested that laryngeal growth and maturation during puberty should make the larynx more robust to inward forces at high minute ventilation [61]. In a 2- to 5-year follow-up study, Maat et al. [41] were unable to show that growth by itself could cure EILO. Patients reported less symptoms but also lower levels of activity, suggesting changes to a lifestyle not challenged by laryngeal airflow limitations. Most patients reported that to be assigned a diagnosis and to actually see what took place in their larynx was important for a perception of safety in relation to exercise and to maintain a reasonable level of physical activity. Among those who had been treated surgically, nearly all were entirely cured [41].
Treatment of EILO
Inclusion to studies aiming to address treatment of EILO (or exercise-induced VCD) was, in the majority of articles, based on symptoms presented by the patients. The same applied to outcome measures; i.e., in most studies inclusion as well as success rates was based on subjective patient reports. Moreover, in most studies patients with EIIS were treated as if they were all suffering from one defined disease entity, often labeled exercise-induced VCD. Few studies have based inclusion and treatment strategies on verifiable findings or created a targeted strategy to deal with this. Given the heterogeneity of laryngeal findings that has been reported in patients with relatively similar symptoms [13, 18, 39], it seems that conclusions should be interpreted very cautiously. Another complicating factor is the role played by placebo effects in studies utilizing open label designs and methods such as psychotherapy or speech therapy [2, 5, 7, 11, 15, 26, 62, 63, 64, 65]. Inhaled ipratropium bromide applied locally prior to activity has been reported to prevent exercise-induced VCD [66]. Different forms of biofeedback techniques have been proposed [67], as has inspiratory muscle training (IMT) [68, 69, 70, 71]. Surgical supraglottoplasty has been used to treat patients with severe supraglottic EILO and positive effects have been reported by several [29, 37, 39, 40, 72, 73, 74]. Selection of patients for surgical treatment should be performed with great care, particularly avoiding those with a primary glottic EILO [40, 41] and potential gains must be weighed against the risk of potential complications. The place for surgery in the treatment of EILO has not been settled.
Video-recorded verification of laryngeal obstruction may be of value not only as a diagnostic tool, but also as a therapeutic measure. Simply observing their own malfunctioning larynx is of help in a majority of patients with mild or moderate disease. The video recordings are also highly educational in the process of providing advice regarding what is a rational respiratory pattern during exercise. However, these are clinical observations, not substantiated scientifically. In conclusion, there is a need for randomized controlled trials with inclusion as well as outcome assessment performed with objective measures.
Concluding remarks
Obstructions of central airways are important causes of exercise-induced inspiratory symptoms (EIIS) in young and otherwise healthy individuals. This is a large, heterogeneous and vastly understudied group of patients. The symptoms are too often confused with those of asthma. Laryngoscopy performed as symptoms evolve during increasing exercise is pivotal, since larynx plays an important role in a majority. Abnormalities vary between patients, and laryngoscopic findings are of value for treatment and further handling. Causal mechanisms are generally poorly understood. The evidence base for most treatment options is weak, but most patients seem to benefit from individualized information and guidance. Surgical treatment may be indicated in well-defined and severe cases. A systematized clinical approach, more and better research utilizing objective methodology as well as randomized controlled treatment trials are of utmost importance in this field of respiratory medicine.
Major funding institutions: Haukeland University Hospital and University of Bergen.
Conflict of interest
There are no financial or other conflicts of interest related to the present paper for any of the authors. Particularly, the patent protecting the commercial rights of the CLE test (US patent # 1/134551) is owned by the hospital and clearly not by the authors.
Supplementary material
Supplementary material 1 (WMV 2434 kb)
Supplementary material 2 (WMV 7379 kb)
Supplementary material 3 (WMV 24146 kb)
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Copyright information
Open AccessThis article is distributed under the terms of the Creative Commons Attribution License which permits any use, distribution, and reproduction in any medium, provided the original author(s) and the source are credited.


text:
Coding standard
Main Page > Development > Development/Coding standard
On this page you will find an overview of some of the coding practices we follow when developing AtoM, and which we look for as part of our Code review process. The AtoM project is based on the symfony (1.4) framework, which is written in PHP. We've adopted the following standards, in addition to symfony's coding standard and best practices for PHP development.
In general, we recommend that anyone wanting to work with AtoM code familiarize themselves with git, the PHP Symfony 1.x framework, Twitter Bootstrap (2.3), and Elasticsearch. You should also be comfortable working in the command-line! Below are a few basic resources to get you started:
- Git Book: http://www.git-scm.com/book
- Symfony 3.4 Coding Standards: https://symfony.com/doc/3.4/contributing/code/standards.html
- Elasticsearch documentation: http://www.elasticsearch.org/guide/
- Unix/Linux command cheat sheet: http://fosswire.com/post/2007/08/unixlinux-command-cheat-sheet/
Variable names
We prefer, whenever possible, using camelCase variables:
$myVariable = 5; // Preferred $my_variable = 5; // Not preferred
There are a lot of variations in what is considered to be camelCase - we prefer starting with a lower-case letter.
Always use braces, even when not necessary:
if ($x) // Preferred { myFunc(); } if ($x) // Not preferred myFunc();
Also, always ensure braces are on their own lines:
if ($x) // Preferred { //... } if ($x) { // Not preferred // ... }
Never use PHP short open tag (
<?); instead, please use the full tag
<?php instead.
To ensure you remember this during development, you can disable short open tags support in your PHP environment (short_open_tag directive in your php.ini file).
count() vs. sizeof()
Always use
count(). Also see below for using
count() to test for empty arrays.
Never use
empty() for checking whether an array value is empty. Instead always use
0 < count(). This is because our arrays may be objects implementing the ArrayAccess interface, in which case
empty() may not behave as expected.
See: http://www.symfony-project.org/book/dev/07-Inside-the-View-Layer#Escaping%20Arrays%20and%20Objects
An advantage of using
count() > 0 over
empty() is that
empty() cannot be called using variable functions.
See: http://php.net/empty
empty() is a language construct and doing so is a syntax error.
Don't use trailing semicolons in templates unless required. Generally the trailing semicolon is implied by the PHP close tag. The trailing semicolon is only required after alternative PHP syntax end control statements (endif, endforeach, endwhile, etc.)
<?php echo $someVar ?> // Good, semicolon is implied by the PHP close tag <?php echo $someVar; ?> // Unnecessary <?php endif; ?> // Necessary
Don't use empty constructor argument lists, since they're not required,
$foo = new Foo; // Good, no argument list $foo = new Foo(); // Unnecessary $foo = new Foo($bar, ...); // Necessary
When it is useful to have a constructor method, either because you can chain methods but not constructors (
create...()->aaa()->bbb() works, but
new Foo->aaa()->bbb() does not), or in order to support constructor overloading (
createFromFoo($foo) and
createFromBar($bar)), or because the actual constructor must have protected visibility, the constructor method should be named like
create...(). It shouldn't be named like
new...() because new is a reserved word in PHP.
Return statements
As per symfony standard, add an empty line before any return statements *except* where it would leave an empty line after an opening curly brace (e.g. a one line function). Empty lines should *never* follow an open curly brace or precede a close curly brace
Use one empty line between functions.
There must not be trailing whitespace at the end of lines.
Line lengths
Lines should be limited to 80 characters or less whenever possible, but may exceed 80 characters if necessary for legibility. Lines should not exceed 120 characters in length. (See: https://www.php-fig.org/psr/psr-12/#23-lines)
null === $foo instead of
is_null($foo). This is because there's no equivalent to
is_null() for "false === $foo" or "0 === $foo", and we prefer to use consistent syntax for "null === $foo", "false === $foo", and "0 === $foo"
Instead of functions with long lists of optional arguments, we prefer passing these arguments in an $options array,
public function foo($required1, $required2, array $options = array()) // Preferred public function foo($required1, $required2, $option1 = null, $option2 = null, ...) // Not preferred
This saves having to pass several null arguments when you want to specify only the last option, which is prone to getting the number of arguments in the function signature wrong, and accidentally specifying the wrong option
It's interesting how symfony mixes associative and ordered options/parameters; see for example:
In the function body, set default values for optional arguments with array addition,
$options += array('option1' => 'foo', 'option2' => 'bar');
Don't use symfony internal URIs. Instead, always use an array of parameters for generating URIs. This is because it's easy to confuse internal and external URIs, and internal URIs add yet another URI format to remember
link_to('link text', array('module' => user', 'action' => 'login')); // Good link_to('link text', 'user/login'); // Bad link_to('link text', '/login/'); // Incorrect
substr() to check if a string begins or ends with another string. It's possible to check if a string begins with another string with
strncmp(), but
strncmp() isn't able to check if a string ends with another string and we prefer to use a consistent pattern for both. Also, the return value of
strncmp() (< 0 if str1 is less than str2 ; > 0 if str1 is greater than str2 , and 0 if they are equal) is confusing.
if (substr($string, 5) == 'HTTP_') // Good if (substr($string, -8) == '_wrapper') // Good if (!strncmp($string, 'HTTP_', 5)) // Awkward if (!strncmp($string, '_wrapper', -8)) // Not supported
Never use the JavaScript pseudo protocol. Always use standard JavaScript events for triggering behavior. Because the "a" tag must have an "href" attribute, use href="#". This is standard practice in YUI (see the tree view) and symfony (see the debug toolbar). A possible advantage of href="#" is that it could possibly be used to support the back button.
  [...] $('.foo').click(foo);


text:
Pocket Roulette Game5055964708436
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text: Posted on 1st September 20191st September 2019 by FOREVERENGLISH — Leave a commentCompetitive Live Stream – Tau vs Necrons – Warhammer 40k While we're waiting for our Fibre upgrade to be installed here's a practice game between Mani & Gaz using the Battlefield Birmingham missions. This Content is Restricted for ELITE Members Only. Sign Up Today and get Unlimited Access to Start Improving Your Game. Join The Elite Username Password Remember Me Forgot Password Post navigationPrevious post: Competitive ITC Battle Report – Deathwatch & Friends vs Chaos Knights – Warhammer 40kNext post: Mani's LGT List!!


text:
Certified environmental management
Compared to other modes of transport shipping compels by an excellent environmental balance. But this fact alone is not a reason for us to sit back and do nothing if we can turn work processes ashore and at sea even more efficient and, thus, environment-friendlier. The protection of climate and environment are integral parts of the corporate policy of Beluga Shipping since acting both economically and ecologically responsible is not at all a contradiction in our eyes.
We have implemented an environment management system according to ISO 14001:2004 for each of our three subdivisions as well as every of our self-managed multipurpose heavy-lift project carriers which is regularly audited by Germanischer Lloyd. Thereby we do not only ensure running our vessel in a "clean" way but do also "green" the work ashore, for example by selecting of our partners or purchasing environment-friendly products. But that is not all: As one of few shipping companies we count on an own Research & Innovation department which actively participates in investigating efficient, groundbreaking technologies. That includes, for example, the towing kite propulsion system for vessels SkySails, the use of solar and fuel cells on board or the implementation of flow resistance reducing hull surfaces, just to name three examples. That makes clear: "Green Shipping" is not just a lip service for us but verifiable reality.
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text:
Game Theory is a name for a collection of analytic tools which economists use to understand strategic interactions. The aim of this course is to learn how to analyze strategic behavior of rational decision makers. We say that decision making is strategic if it involves taking into account what other agents want, know, believe and do. Strategic behavior is an important component in interactions such as market competition between firms, bilateral bargaining, auctions, voting, and information transmission. In this course we cover strategic-form games with complete information, strategic-form games with incomplete information, dynamic games, and equilibrium concepts for analyzing these games. The focus of the course is on three equally important fronts: First, the students should get a good understanding (and some experience) of how to model a strategic environment as a game. Second, the students will learn and how to solve a game-theoretic model appropriately. The definitions and propositions included in the course aim .to provide analytical tools for students achieving this. Third, the course will contain an overview of some classic applications of game theory mostly in economics. The applications are put forward to explain economic phenomena, to illustrate theories, and in some cases to add fun to a theoretical course.
Sunday & Tuesday 8:00 – 9:30, Classroom 6
Room 118; Tuesday 9:30 – 10:30 or by appointment (email: email@example.com)
The evaluation of the course is based on
quizzes (15%)
mid-term exam (40%)
final exam (45%)
Students performance in classes has a 5% bonus mark.
Osborne, Martin & Ariel Rubinstein (OR); A Course in Game Theory; MIT Press. Osborne, Martin (Os); An introduction to Game Theory; Oxford University Press.
Other references which might be used are (some other papers and books might be added to the list later in the term): Gibbons, Robert; A Primer in Game Theory; Prentice Hall. Fudenberg Drew & Jean Tirole; Game Theory; MIT Press.
Quizzes: TBC
Mid-Term: Wednesday 1395/01/30 at 9:00 am
Final: Saturday 1395/03/31 at 9:00 am


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