title: postgresql.conf optimization
body: <p>My postgresql server is extremely slow. Especially when I execute several queries at the same time in different threads, which somtimes causes the postgresql server to be unresponsive for 5 to 15 seconds. I wonder if I made a mistake in the postgresql.conf.</p>
  
  <p>My dedicated server has 2 cores and 4 gb of ram, and a standard SATA-2 disk. There are 6gb of data in the postgres db (version 8.4) and a few hundred users simultaneously connected. I'm using JDBC to access postgress, running 1 to 10 simultaneous threads accessing the database. My server is a debian lenny. The Cpu is not used at 100%, neither is the memory.</p>
  
  <p>Thanks for any sort of help.</p>
  
  <pre><code>    # -----------------------------
      # PostgreSQL configuration file
      # -----------------------------
      #
      # This file consists of lines of the form:
      #
      #   name = value
      #
      # (The "=" is optional.)  Whitespace may be used.  Comments are introduced with
      # "#" anywhere on a line.  The complete list of parameter names and allowed
      # values can be found in the PostgreSQL documentation.
      #
      # The commented-out settings shown in this file represent the default values.
      # Re-commenting a setting is NOT sufficient to revert it to the default value;
      # you need to reload the server.
      #
      # This file is read on server startup and when the server receives a SIGHUP
      # signal.  If you edit the file on a running system, you have to SIGHUP the
      # server for the changes to take effect, or use "pg_ctl reload".  Some
      # parameters, which are marked below, require a server shutdown and restart to
      # take effect.
      #
      # Any parameter can also be given as a command-line option to the server, e.g.,
      # "postgres -c log_connections=on".  Some parameters can be changed at run time
      # with the "SET" SQL command.
      #
      # Memory units:  kB = kilobytes        Time units:  ms  = milliseconds
      #                MB = megabytes                     s   = seconds
      #                GB = gigabytes                     min = minutes
      #                                                   h   = hours
      #                                                   d   = days
  
  
      #------------------------------------------------------------------------------
      # FILE LOCATIONS
      #------------------------------------------------------------------------------
  
      # The default values of these variables are driven from the -D command-line
      # option or PGDATA environment variable, represented here as ConfigDir.
  
      data_directory = '/home/keyja/dbdata'       # use data in another directory
                          # (change requires restart)
      hba_file = '/etc/postgresql/8.4/main/pg_hba.conf'   # host-based authentication file
                          # (change requires restart)
      ident_file = '/etc/postgresql/8.4/main/pg_ident.conf'   # ident configuration file
                          # (change requires restart)
  
      # If external_pid_file is not explicitly set, no extra PID file is written.
      external_pid_file = '/var/run/postgresql/8.4-main.pid'      # write an extra PID file
                          # (change requires restart)
  
  
      #------------------------------------------------------------------------------
      # CONNECTIONS AND AUTHENTICATION
      #------------------------------------------------------------------------------
  
      # - Connection Settings -
  
      listen_addresses = '*'      # what IP address(es) to listen on;
                          # comma-separated list of addresses;
                          # defaults to 'localhost', '*' = all
                          # (change requires restart)
      port = 5432             # (change requires restart)
      max_connections = 100           # (change requires restart)
      # Note:  Increasing max_connections costs ~400 bytes of shared memory per 
      # connection slot, plus lock space (see max_locks_per_transaction).
      #superuser_reserved_connections = 3 # (change requires restart)
      unix_socket_directory = '/var/run/postgresql'       # (change requires restart)
      #unix_socket_group = ''         # (change requires restart)
      #unix_socket_permissions = 0777     # begin with 0 to use octal notation
                          # (change requires restart)
      #bonjour_name = ''          # defaults to the computer name
                          # (change requires restart)
  
      # - Security and Authentication -
  
      #authentication_timeout = 1min      # 1s-600s
      ssl = true              # (change requires restart)
      #ssl_ciphers = 'ALL:!ADH:!LOW:!EXP:!MD5:@STRENGTH'  # allowed SSL ciphers
                          # (change requires restart)
      #ssl_renegotiation_limit = 512MB    # amount of data between renegotiations
      #password_encryption = on
      #db_user_namespace = off
  
      # Kerberos and GSSAPI
      #krb_server_keyfile = ''
      #krb_srvname = 'postgres'       # (Kerberos only)
      #krb_caseins_users = off
  
      # - TCP Keepalives -
      # see "man 7 tcp" for details
  
      #tcp_keepalives_idle = 0        # TCP_KEEPIDLE, in seconds;
                          # 0 selects the system default
      #tcp_keepalives_interval = 0        # TCP_KEEPINTVL, in seconds;
                          # 0 selects the system default
      #tcp_keepalives_count = 0       # TCP_KEEPCNT;
                          # 0 selects the system default
  
  
      #------------------------------------------------------------------------------
      # RESOURCE USAGE (except WAL)
      #------------------------------------------------------------------------------
  
      # - Memory -
  
      shared_buffers = 1024MB         # min 128kB
                          # (change requires restart)
      #temp_buffers = 8MB         # min 800kB
      #max_prepared_transactions = 0      # zero disables the feature
                          # (change requires restart)
      # Note:  Increasing max_prepared_transactions costs ~600 bytes of shared memory
      # per transaction slot, plus lock space (see max_locks_per_transaction).
      # It is not advisable to set max_prepared_transactions nonzero unless you
      # actively intend to use prepared transactions.
      work_mem = 100MB                # min 64kB
      maintenance_work_mem = 160MB        # min 1MB
      #max_stack_depth = 2MB          # min 100kB
  
      # - Kernel Resource Usage -
  
      #max_files_per_process = 1000       # min 25
                          # (change requires restart)
      #shared_preload_libraries = ''      # (change requires restart)
  
      # - Cost-Based Vacuum Delay -
  
      #vacuum_cost_delay = 0ms        # 0-100 milliseconds
      #vacuum_cost_page_hit = 1       # 0-10000 credits
      #vacuum_cost_page_miss = 10     # 0-10000 credits
      #vacuum_cost_page_dirty = 20        # 0-10000 credits
      #vacuum_cost_limit = 200        # 1-10000 credits
  
      # - Background Writer -
  
      #bgwriter_delay = 200ms         # 10-10000ms between rounds
      #bgwriter_lru_maxpages = 100        # 0-1000 max buffers written/round
      #bgwriter_lru_multiplier = 2.0      # 0-10.0 multipler on buffers scanned/round
  
      # - Asynchronous Behavior -
  
      #effective_io_concurrency = 1       # 1-1000. 0 disables prefetching
  
  
      #------------------------------------------------------------------------------
      # WRITE AHEAD LOG
      #------------------------------------------------------------------------------
  
      # - Settings -
  
      fsync = off             # turns forced synchronization on or off
      #synchronous_commit = on        # immediate fsync at commit
      #wal_sync_method = fsync        # the default is the first option 
                          # supported by the operating system:
                          #   open_datasync
                          #   fdatasync (default on Linux)
                          #   fsync
                          #   fsync_writethrough
                          #   open_sync
      full_page_writes = off          # recover from partial page writes
      #wal_buffers = 64kB         # min 32kB
                          # (change requires restart)
      #wal_writer_delay = 200ms       # 1-10000 milliseconds
  
      #commit_delay = 0           # range 0-100000, in microseconds
      #commit_siblings = 5            # range 1-1000
  
      # - Checkpoints -
  
      checkpoint_segments = 20        # in logfile segments, min 1, 16MB each
      #checkpoint_timeout = 5min      # range 30s-1h
      checkpoint_completion_target = 0.9  # checkpoint target duration, 0.0 - 1.0
      #checkpoint_warning = 30s       # 0 disables
  
      # - Archiving -
  
      #archive_mode = off     # allows archiving to be done
                      # (change requires restart)
      #archive_command = ''       # command to use to archive a logfile segment
      #archive_timeout = 0        # force a logfile segment switch after this
                      # number of seconds; 0 disables
  
  
      #------------------------------------------------------------------------------
      # QUERY TUNING
      #------------------------------------------------------------------------------
  
      # - Planner Method Configuration -
  
      #enable_bitmapscan = on
      #enable_hashagg = on
      #enable_hashjoin = on
      #enable_indexscan = on
      #enable_mergejoin = on
      #enable_nestloop = on
      #enable_seqscan = on
      #enable_sort = on
      #enable_tidscan = on
  
      # - Planner Cost Constants -
  
      #seq_page_cost = 1.0            # measured on an arbitrary scale
      #random_page_cost = 4.0         # same scale as above
      #cpu_tuple_cost = 0.01          # same scale as above
      #cpu_index_tuple_cost = 0.005       # same scale as above
      #cpu_operator_cost = 0.0025     # same scale as above
      effective_cache_size = 256MB
  
      # - Genetic Query Optimizer -
  
      #geqo = on
      #geqo_threshold = 12
      #geqo_effort = 5            # range 1-10
      #geqo_pool_size = 0         # selects default based on effort
      #geqo_generations = 0           # selects default based on effort
      #geqo_selection_bias = 2.0      # range 1.5-2.0
  
      # - Other Planner Options -
  
      #default_statistics_target = 100    # range 1-10000
      #constraint_exclusion = partition   # on, off, or partition
      #cursor_tuple_fraction = 0.1        # range 0.0-1.0
      #from_collapse_limit = 8
      #join_collapse_limit = 8        # 1 disables collapsing of explicit 
                          # JOIN clauses
  
  
      #------------------------------------------------------------------------------
      # ERROR REPORTING AND LOGGING
      #------------------------------------------------------------------------------
  
      # - Where to Log -
  
      log_destination = 'stderr'      # Valid values are combinations of
                          # stderr, csvlog, syslog and eventlog,
                          # depending on platform.  csvlog
                          # requires logging_collector to be on.
  
      # This is used when logging to stderr:
      logging_collector = ON      # Enable capturing of stderr and csvlog
                          # into log files. Required to be on for
                          # csvlogs.
                          # (change requires restart)
  
      # These are only used if logging_collector is on:
      log_directory = 'pg_log'        # directory where log files are written,
                          # can be absolute or relative to PGDATA
      log_filename = 'postgresql_%A.log'  # log file name pattern,
                          # can include strftime() escapes
      log_truncate_on_rotation = on       # If on, an existing log file of the
                          # same name as the new log file will be
                          # truncated rather than appended to.
                          # But such truncation only occurs on
                          # time-driven rotation, not on restarts
                          # or size-driven rotation.  Default is
                          # off, meaning append to existing files
                          # in all cases.
      log_rotation_age = 1d           # Automatic rotation of logfiles will
                          # happen after that time.  0 disables.
      #log_rotation_size = 10MB       # Automatic rotation of logfiles will 
                          # happen after that much log output.
                          # 0 disables.
  
      # These are relevant when logging to syslog:
      #syslog_facility = 'LOCAL0'
      #syslog_ident = 'postgres'
  
      silent_mode = on            # Run server silently.
                          # DO NOT USE without syslog or
                          # logging_collector
                          # (change requires restart)
  
  
      # - When to Log -
  
      #client_min_messages = notice       # values in order of decreasing detail:
                          #   debug5
                          #   debug4
                          #   debug3
                          #   debug2
                          #   debug1
                          #   log
                          #   notice
                          #   warning
                          #   error
  
      #log_min_messages = warning     # values in order of decreasing detail:
                          #   debug5
                          #   debug4
                          #   debug3
                          #   debug2
                          #   debug1
                          #   info
                          #   notice
                          #   warning
                          #   error
                          #   log
                          #   fatal
                          #   panic
  
      #log_error_verbosity = default      # terse, default, or verbose messages
  
      #log_min_error_statement = error    # values in order of decreasing detail:
                          #   debug5
                          #   debug4
                          #   debug3
                          #   debug2
                          #   debug1
                          #   info
                          #   notice
                          #   warning
                          #   error
                          #   log
                          #   fatal
                          #   panic (effectively off)
  
      log_min_duration_statement = 1000   # -1 is disabled, 0 logs all statements
                          # and their durations, &gt; 0 logs only
                          # statements running at least this number
                          # of milliseconds
  
  
      # - What to Log -
  
      #debug_print_parse = off
      #debug_print_rewritten = off
      #debug_print_plan = off
      #debug_pretty_print = on
      #log_checkpoints = off
      #log_connections = off
      #log_disconnections = off
      log_duration = off
      #log_hostname = off
      log_line_prefix = '%t [%p]: [%l-1] '            # special values:
                          #   %u = user name
                          #   %d = database name
                          #   %r = remote host and port
                          #   %h = remote host
                          #   %p = process ID
                          #   %t = timestamp without milliseconds
                          #   %m = timestamp with milliseconds
                          #   %i = command tag
                          #   %c = session ID
                          #   %l = session line number
                          #   %s = session start timestamp
                          #   %v = virtual transaction ID
                          #   %x = transaction ID (0 if none)
                          #   %q = stop here in non-session
                          #        processes
                          #   %% = '%'
                          # e.g. '&lt;%u%%%d&gt; '
      #log_lock_waits = off           # log lock waits &gt;= deadlock_timeout
      log_statement = 'all'           # none, ddl, mod, all
      #log_temp_files = -1            # log temporary files equal or larger
                          # than the specified size in kilobytes;
                          # -1 disables, 0 logs all temp files
      #log_timezone = unknown         # actually, defaults to TZ environment
                          # setting
  
  
      #------------------------------------------------------------------------------
      # RUNTIME STATISTICS
      #------------------------------------------------------------------------------
  
      # - Query/Index Statistics Collector -
  
      #track_activities = on
      track_counts = on
      #track_functions = none         # none, pl, all
      #track_activity_query_size = 1024
      #update_process_title = on
      #stats_temp_directory = 'pg_stat_tmp'
  
  
      # - Statistics Monitoring -
  
      #log_parser_stats = off
      #log_planner_stats = off
      #log_executor_stats = off
      #log_statement_stats = off
  
  
      #------------------------------------------------------------------------------
      # AUTOVACUUM PARAMETERS
      #------------------------------------------------------------------------------
  
      autovacuum = on         # Enable autovacuum subprocess?  'on' 
                          # requires track_counts to also be on.
      log_autovacuum_min_duration = -1    # -1 disables, 0 logs all actions and
                          # their durations, &gt; 0 logs only
                          # actions running at least this number
                          # of milliseconds.
      autovacuum_max_workers = 3      # max number of autovacuum subprocesses
      autovacuum_naptime = 1min       # time between autovacuum runs
      autovacuum_vacuum_threshold = 50    # min number of row updates before
                          # vacuum
      autovacuum_analyze_threshold = 50   # min number of row updates before 
                          # analyze
      autovacuum_vacuum_scale_factor = 0.2    # fraction of table size before vacuum
      autovacuum_analyze_scale_factor = 0.1   # fraction of table size before analyze
      autovacuum_freeze_max_age = 200000000   # maximum XID age before forced vacuum
                          # (change requires restart)
      autovacuum_vacuum_cost_delay = 20ms # default vacuum cost delay for
                          # autovacuum, in milliseconds;
                          # -1 means use vacuum_cost_delay
      autovacuum_vacuum_cost_limit = -1   # default vacuum cost limit for
                          # autovacuum, -1 means use
                          # vacuum_cost_limit
  
  
      #------------------------------------------------------------------------------
      # CLIENT CONNECTION DEFAULTS
      #------------------------------------------------------------------------------
  
      # - Statement Behavior -
  
      #search_path = '"$user",public'     # schema names
      #default_tablespace = ''        # a tablespace name, '' uses the default
      #temp_tablespaces = ''          # a list of tablespace names, '' uses
                          # only default tablespace
      #check_function_bodies = on
      #default_transaction_isolation = 'read committed'
      #default_transaction_read_only = off
      #session_replication_role = 'origin'
      #statement_timeout = 0          # in milliseconds, 0 is disabled
      #vacuum_freeze_min_age = 50000000
      #vacuum_freeze_table_age = 150000000
      #xmlbinary = 'base64'
      #xmloption = 'content'
  
      # - Locale and Formatting -
  
      datestyle = 'iso, dmy'
      #intervalstyle = 'postgres'
      #timezone = unknown         # actually, defaults to TZ environment
                          # setting
      #timezone_abbreviations = 'Default'     # Select the set of available time zone
                          # abbreviations.  Currently, there are
                          #   Default
                          #   Australia
                          #   India
                          # You can create your own file in
                          # share/timezonesets/.
      #extra_float_digits = 0         # min -15, max 2
      #client_encoding = sql_ascii        # actually, defaults to database
                          # encoding
  
      # These settings are initialized by initdb, but they can be changed.
      lc_messages = 'en_GB'           # locale for system error message
                          # strings
      lc_monetary = 'en_GB'           # locale for monetary formatting
      lc_numeric = 'en_GB'            # locale for number formatting
      lc_time = 'en_GB'               # locale for time formatting
  
      # default configuration for text search
      default_text_search_config = 'pg_catalog.english'
  
      # - Other Defaults -
  
      #dynamic_library_path = '$libdir'
      #local_preload_libraries = ''
  
  
      #------------------------------------------------------------------------------
      # LOCK MANAGEMENT
      #------------------------------------------------------------------------------
  
      #deadlock_timeout = 1s
      #max_locks_per_transaction = 64     # min 10
                          # (change requires restart)
      # Note:  Each lock table slot uses ~270 bytes of shared memory, and there are
      # max_locks_per_transaction * (max_connections + max_prepared_transactions)
      # lock table slots.
  
  
      #------------------------------------------------------------------------------
      # VERSION/PLATFORM COMPATIBILITY
      #------------------------------------------------------------------------------
  
      # - Previous PostgreSQL Versions -
  
      #add_missing_from = off
      #array_nulls = on
      #backslash_quote = safe_encoding    # on, off, or safe_encoding
      #default_with_oids = off
      #escape_string_warning = on
      #regex_flavor = advanced        # advanced, extended, or basic
      #sql_inheritance = on
      #standard_conforming_strings = off
      #synchronize_seqscans = on
  
      # - Other Platforms and Clients -
  
      #transform_null_equals = off
  
  
      #------------------------------------------------------------------------------
      # CUSTOMIZED OPTIONS
      #------------------------------------------------------------------------------
  
      #custom_variable_classes = ''       # list of custom variable class names
  </code></pre>