Note: Contributed by Massimo Dal Zotto
The optional file data/pg_options contains runtime options used by the backend to control trace messages and other backend tunable parameters. The file is re-read by a backend when it receives a SIGHUP signal, making thus possible to change run-time options on the fly without needing to restart Postgres. The options specified in this file may be debugging flags used by the trace package (backend/utils/misc/trace.c) or numeric parameters which can be used by the backend to control its behaviour.
All pg_options are initialized to zero at backend startup. New or modified options will be read by all new backends when they are started. To make effective any changes for all running backends we need to send a SIGHUP to the postmaster. The signal will be automatically sent to all the backends. We can also activate the changes only for a specific backend by sending the SIGHUP directly to it.
pg_options can also be specified with the -T switch of Postgres:
postgres options -T "verbose=2,query,hostlookup-"
The functions used for printing errors and debug messages can now make use of the syslog(2) facility. Message printed to stdout or stderr are prefixed by a timestamp containing also the backend pid:
#timestamp #pid #message 980127.17:52:14.173  StartTransactionCommand 980127.17:52:14.174  ProcessUtility: drop table t; 980127.17:52:14.186  SIIncNumEntries: table is 70% full 980127.17:52:14.186  Async_NotifyHandler 980127.17:52:14.186  Waking up sleeping backend process 980127.19:52:14.292  Async_NotifyFrontEnd 980127.19:52:14.413  Async_NotifyFrontEnd done 980127.19:52:14.466  Async_NotifyHandler done
This format improves readability of the logs and allows people to understand exactly which backend is doing what and at which time. It also makes easier to write simple awk or perl scripts which monitor the log to detect database errors or problem, or to compute transaction time statistics.
Messages printed to syslog use the log facility LOG_LOCAL0. The use of syslog can be controlled with the syslog pg_option. Unfortunately many functions call directly printf() to print their messages to stdout or stderr and this output can't be redirected to syslog or have timestamps in it. It would be advisable that all calls to printf would be replaced with the PRINTF macro and output to stderr be changed to use EPRINTF instead so that we can control all output in a uniform way.
The format of the pg_options file is as follows:
# comment option=integer_value # set value for option option # set option = 1 option+ # set option = 1 option- # set option = 0Note that keyword can also be an abbreviation of the option name defined in backend/utils/misc/trace.c.
Example 7-1. pg_options File
For example my pg_options file contains the following values:
verbose=2 query hostlookup showportnumber
The options currently defined are:
Global trace flag. Allowed values are:
Trace messages enabled individually
Enable all trace messages
Disable all trace messages
Verbosity flag. Allowed values are:
No messages. This is the default.
Print information messages.
Print more information messages.
Query trace flag. Allowed values are:
Don't print query.
Print a condensed query in one line.
Print the full query.
Print query plan.
Print parser output.
Print rewritten query.
Pretty-print query plan.
Pretty-print parser output.
Pretty-print rewritten query.
Print parser statistics.
Print planner statistics.
Print executor statistics.
Currently unused but needed to enable features in the future.
Trace user locks.
Trace spin locks.
Trace notify functions.
Minimum relation oid traced by locks.
oid, if not zero, of relation traced by locks.
Deadlock check timer.
syslog flag. Allowed values are:
Messages to stdout/stderr.
Messages to stdout/stderr and syslog.
Messages only to syslog.
Enable hostname lookup in ps_status.
Show port number in ps_status.
Disable fsync on a per-backend basis.