Snapshot Functions¶
This chapter is intended to give detailed information about several snapshot functions, provided in the PgPerf package, to deal with performance snaphsots.
Snapshot Function List¶
| Function Name | Description |
|---|---|
| pgperf.create_snapshot(level) | Takes a new snapshot. |
| pgperf.delete_snapshot(snapid) | Drops a snapshot specified by the snapshot id. |
| pgperf.purge_snapshots(interval) | Drops snapshots older than the specified period. |
| pgperf.get_interval(snapid1, snapid2) | Gets an interval (in second) between two snapshots. |
pgperf.create_snapshot() Function¶
Description¶
pgperf.create_snapshot() function takes a snapshot of the performance statistics, which can be obtained in the PostgreSQL database, and stores them in the snapshot tables.
Declaration¶
integer pgperf.create_snapshot(integer level)
Parameters¶
| Name | Type | Description |
|---|---|---|
| level | integer | Snapshot level to be taken. |
Unfortunately, heavy performance impact could sometimes be generated while taking a snapshot for all the performance statistics available in the database.
To avoid that, pgperf.create_snapshot() function allows DBA to obtain a snapshot with less performance impact by specifying the snapshot level. Then, DBA can avoid taking a snapshot which generates heavy performance impact so frequently.
| Snapshot Level | Snapshot Contents |
|---|---|
| 1 | Obtains a snapshot of the basic access statistics and the session statistics. pg_stat_database, pg_database_size() pg_stat_user_tables, pg_statio_user_tables pg_stat_user_indexes, pg_statio_user_indexes pg_relation_size(), pg_total_relation_size() pg_current_xlog_location(), pg_current_xlog_insert_location() pg_stat_bgwriter pg_stat_activity, pg_locks, pg_stat_statements |
| 2 | In addition to the level 1, obtains a snapshot of the optimizer statistics. pg_statistic |
| 3 | Not used. |
| 4 | In addition to the level 2, obtains a snapshot of the table/index fragmentation statistics. pgstattuple(), pgstatindex() |
| 5 | Not used. |
pgperf.delete_snapshot() Function¶
Description¶
pgperf.delete_snapshot() function deletes a snapshot of the performance statistics specified by the snapshot id.
Declaration¶
integer pgperf.delete_snapshot(integer snapid);
Parameters¶
| Name | Type | Description |
|---|---|---|
| snapid | integer | A snapshot id accociated with the snapshot to be deleted. |
pgperf.purge_snapshots() Function¶
Description¶
pgperf.purge_snapshots() function purges older performance snapshots at once.
Declaration¶
integer pgperf.purge_snapshots(interval period);
Parameters¶
| Name | Type | Description |
|---|---|---|
| period | interval | A period of the snapshots to be kept in the snapshot tables. |
This function drops snapshots older than the period (interval) specified by the parameter period .
See the PostgreSQL manual for more details about how to express an interval value.
pgperf.get_interval() Function¶
Description¶
pgperf.get_interval() function obtains an interval between two snapshots.
This function is intended to give some convenience to convert an obtained value into a ‘per-second’ value, particularly in SQL scripts.
Declaration¶
integer pgperf.get_interval(integer snapid1, integer snapid2)
Parameters¶
| Name | Type | Description |
|---|---|---|
| snapid1 | integer | A snapshot id at the start point. |
| snapid2 | integer | A snapshot id at the end point. |