InnoDB Troubleshooting value column to run report-generating queries on that column using SQL. See Section 15.22, “InnoDB Limits”  for details. The following general guidelines apply to troubleshooting  InnoDB  problems: InnoDB  temporarily enables standard  InnoDB  Monitor output under the following conditions: 3390 15.21.1 Troubleshooting InnoDB I/O Problems •If you suspect that a table is corrupt, run  CHECK TABLE  on that table. •Over 67% of the buffer pool is occupied by lock heaps or the adaptive hash index • InnoDB  cannot find free blocks in the buffer pool •A long semaphore wait • Enable the  InnoDB  Monitors to obtain information about a problem (see Section 15.17, “InnoDB Monitors” ). If the problem is performance-related, or your server appears to be hung, you should enable the standard Monitor to print information about the internal state of  InnoDB . If the problem is with locks, enable the Lock Monitor. If the problem is with table creation, tablespaces, or data dictionary operations, refer to the InnoDB Information Schema system tables to examine contents of the  InnoDB  internal data dictionary. •When troubleshooting, it is usually best to run the MySQL server from the command prompt, rather than through  mysqld_safe  or as a Windows service. You can then see what  mysqld  prints to the console, and so have a better grasp of what is going on. On Windows, start  mysqld  with the  --console  option to direct the output to the console window. •If the issue is related to the  InnoDB  data dictionary, see Section 15.21.3, “Troubleshooting InnoDB Data Dictionary Operations” . •If the failure is related to a deadlock, run with the  innodb_print_all_deadlocks  option enabled so that details about each deadlock are printed to the MySQL server error log. For information about deadlocks, see Section 15.7.5, “Deadlocks in InnoDB” . •When an operation fails or you suspect a bug, look at the MySQL server error log (see Section 5.4.2, “The Error Log” ). Server Error Message Reference provides troubleshooting information for some of the common  InnoDB -specific errors that you may encounter. • memcached  connections are blocked from accessing tables that contain an indexed virtual column. Accessing an indexed virtual column requires a callback to the server, but a  memcached  connection does not have access to the server code. •There is no restriction or check in place to validate character set settings.  memcached  stores and retrieves keys and values in bytes and is therefore not character set sensitive. However, you must ensure that the  memcached  client and the MySQL table use the same character set. •If you share configuration files across MySQL servers of different versions, using the latest configuration options for the  daemon_memcached  plugin could cause startup errors on older MySQL versions. To avoid compatibility problems, use the  loose  prefix with option names. For example, use  loose- daemon_memcached_option=’-c 64’  instead of  daemon_memcached_option=’-c 64’ . •The maximum size for the key-value combination is 1 MB. 15.21 InnoDB Troubleshooting