pgsentinel – sampling active session history
PostgreSQL provides session activity. However, in order to gather activity
behavior user have to sample the pg_stat_activity view multiple times.
pgsentinel is an extension to record active session history and also link
the activity with query statistics (
The module must be loaded by adding
shared_preload_libraries in postgresql.conf, means that a server restart
is needed to add or remove the module.
pgsentinel is enabled, it collects the history of session activity:
- It's implemented as in-memory ring buffer where samples are written with given (configurable) period. Therefore, user can see some number of recent samples depending on history size (configurable).
In combination with
pg_stat_statements this extension can also link the session activity with
pgsentinel launches special background worker for gathering the
pgsentinel is implemented as an extension and not available in default
PostgreSQL installation. It is available from
under the same license as
GNU AFFERO GENERAL PUBLIC LICENSE
and supports PostgreSQL 9.6+.
pgsentinel is a PostgreSQL extension which requires PostgreSQL 9.6 or
higher. Before build and install you should ensure the following:
- PostgreSQL version is 9.6 or higher.
- You built PostgreSQL from source.
- Your PATH variable is configured so that
pg_configcommand available, or set PG_CONFIG variable.
Typical installation procedure may look like this:
As pgsentinel uses the
pg_stat_statements extension (officially bundled with PostgreSQL) for tracking which queries get executed in your database, add the following entries to your postgres.conf:
$ shared_preload_libraries = 'pg_stat_statements,pgsentinel' $ # Icncrease the max size of the query strings Postgres records $ track_activity_query_size = 2048 $ # Track statements generated by stored procedures as well $ pg_stat_statements.track = all
restart the postgresql daemon and create the extension:
$ git clone https://github.com/pgsentinel/pgsentinel.git $ cd pgsentinel/src $ make $ sudo make install $ psql DB -c "CREATE EXTENSION pgsentinel;"
pgsentinel reports the active session history activity through the
|ash_time||timestamp with time zone|
|backend_start||timestamp with time zone|
|xact_start||timestamp with time zone|
|query_start||timestamp with time zone|
|state_change||timestamp with time zone|
You could see it as samplings of
pg_stat_activity providing more information:
ash_time: the sampling time
top_level_query: the top level statement (in case PL/pgSQL is used)
query: the statement being executed (not normalised, as it is in
pg_stat_statements, means you see the values)
cmdtype: the statement type (SELECT,UPDATE,INSERT,DELETE,UTILITY,UNKNOWN,NOTHING)
queryid: the queryid of the statement which links to pg_stat_statements
blockers: the number of blockers
blockerpid: the pid of the blocker (if blockers = 1), the pid of one blocker (if blockers > 1)
blocker_state: state of the blocker (state of the blockerpid)
The worker is controlled by the following GUCs:.
|Parameter name||Data type||Description||Default value||Min value|
|pgsentinel_ash.sampling_period||int4||Period for history sampling in seconds||1||1|
|pgsentinel_ash.max_entries||int4||Size of history in-memory ring buffer||1000||1000|
|pgsentinel.db_name||char||database the worker should connect to||postgres|
Remarks for PostgreSQL 9.6
backend_typefield does not exist into the
backend_typefield exists into the
pg_active_session_historyview and is always NULL (as a consequence of the previous remark)
See how to query the view in this short video
Please, notice, that
pgsentinel is still in beta testing so may contain some bugs. Don't hesitate to raise
issues at github with
your bug report.
If you're lacking of some functionality in
then you're welcome to make pull requests.
- Bertrand Drouvot email@example.com, Metz, France