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18.15. Developer Options

The following parameters are intended for work on the PostgreSQL source, and in some cases to assist with recovery of severely damaged databases. There should be no reason to use them in a production database setup. As such, they have been excluded from the sample postgresql.conf file. Note that many of these parameters require special source compilation flags to work at all.

allow_system_table_mods (boolean)

Allows modification of the structure of system tables. This is used by initdb. This parameter can only be set at server start.

debug_assertions (boolean)

Turns on various assertion checks. This is a debugging aid. If you are experiencing strange problems or crashes you might want to turn this on, as it might expose programming mistakes. To use this parameter, the macro USE_ASSERT_CHECKING must be defined when PostgreSQL is built (accomplished by the configure option --enable-cassert). Note that debug_assertions defaults to on if PostgreSQL has been built with assertions enabled.

ignore_system_indexes (boolean)

Ignore system indexes when reading system tables (but still update the indexes when modifying the tables). This is useful when recovering from damaged system indexes. This parameter cannot be changed after session start.

post_auth_delay (integer)

If nonzero, a delay of this many seconds occurs when a new server process is started, after it conducts the authentication procedure. This is intended to give an opportunity to attach to the server process with a debugger. This parameter cannot be changed after session start.

pre_auth_delay (integer)

If nonzero, a delay of this many seconds occurs just after a new server process is forked, before it conducts the authentication procedure. This is intended to give an opportunity to attach to the server process with a debugger to trace down misbehavior in authentication. This parameter can only be set in the postgresql.conf file or on the server command line.

trace_notify (boolean)

Generates a great amount of debugging output for the LISTEN and NOTIFY commands. client_min_messages or log_min_messages must be DEBUG1 or lower to send this output to the client or server log, respectively.

trace_sort (boolean)

If on, emit information about resource usage during sort operations. This parameter is only available if the TRACE_SORT macro was defined when PostgreSQL was compiled. (However, TRACE_SORT is currently defined by default.)

trace_locks (boolean)

If on, emit information about lock usage. Information dumped includes the type of lock operation, the type of lock and the unique identifier of the object being locked or unlocked. Also included are bitmasks for the lock types already granted on this object as well as for the lock types awaited on this object. For each lock type a count of the number of granted locks and waiting locks is also dumped as well as the totals. An example of the log file output is shown here:

LOG: LockAcquire: new: lock(0xb7acd844) id(24688,24696,0,0,0,1) grantMask(0) req(0,0,0,0,0,0,0)=0 grant(0,0,0,0,0,0,0)=0 wait(0) type(AccessShareLock)

LOG: GrantLock: lock(0xb7acd844) id(24688,24696,0,0,0,1) grantMask(2) req(1,0,0,0,0,0,0)=1 grant(1,0,0,0,0,0,0)=1 wait(0) type(AccessShareLock)

LOG: UnGrantLock: updated: lock(0xb7acd844) id(24688,24696,0,0,0,1) grantMask(0) req(0,0,0,0,0,0,0)=0 grant(0,0,0,0,0,0,0)=0 wait(0) type(AccessShareLock)

LOG: CleanUpLock: deleting: lock(0xb7acd844) id(24688,24696,0,0,0,1) grantMask(0) req(0,0,0,0,0,0,0)=0 grant(0,0,0,0,0,0,0)=0 wait(0) type(INVALID)

Details of the structure being dumped may be found in src/include/storage/lock.h

This parameter is only available if the LOCK_DEBUG macro was defined when PostgreSQL was compiled.

trace_lwlocks (boolean)

If on, emit information about lightweight lock usage. Lightweight locks are intended primarily to provide mutual exclusion of access to shared-memory data structures.

This parameter is only available if the LOCK_DEBUG macro was defined when PostgreSQL was compiled.

trace_userlocks (boolean)

If on, emit information about user lock usage. Output is the same as for trace_locks, only for advisory locks.

This parameter is only available if the LOCK_DEBUG macro was defined when PostgreSQL was compiled.

trace_lock_oidmin (integer)

If set, do not trace locks for tables below this OID. (use to avoid output on system tables)

This parameter is only available if the LOCK_DEBUG macro was defined when PostgreSQL was compiled.

trace_lock_table (integer)

Unconditionally trace locks on this table (OID).

This parameter is only available if the LOCK_DEBUG macro was defined when PostgreSQL was compiled.

debug_deadlocks (boolean)

If set, dumps information about all current locks when a DeadLockTimeout occurs.

This parameter is only available if the LOCK_DEBUG macro was defined when PostgreSQL was compiled.

log_btree_build_stats (boolean)

If set, logs system resource usage statistics (memory and CPU) on various btree operations.

This parameter is only available if the BTREE_BUILD_STATS macro was defined when PostgreSQL was compiled.

wal_debug (boolean)

If on, emit WAL-related debugging output. This parameter is only available if the WAL_DEBUG macro was defined when PostgreSQL was compiled.

zero_damaged_pages (boolean)

Detection of a damaged page header normally causes PostgreSQL to report an error, aborting the current command. Setting zero_damaged_pages to on causes the system to instead report a warning, zero out the damaged page, and continue processing. This behavior will destroy data, namely all the rows on the damaged page. But it allows you to get past the error and retrieve rows from any undamaged pages that might be present in the table. So it is useful for recovering data if corruption has occurred due to hardware or software error. You should generally not set this on until you have given up hope of recovering data from the damaged page(s) of a table. The default setting is off, and it can only be changed by a superuser.

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