Aurora PostgreSQL Limitless Database functions

The limitless_backend_dsid function returns the distributed session ID for the current session. A distributed session runs on a router in a DB shard group and involves backend processes on one or more shards in the DB shard group.

The following example shows how to use the limitless_backend_dsid function.

SELECT rds_aurora.limitless_backend_dsid();

limitless_backend_dsid
------------------------
8CACD7B04D0FC2A5
(1 row)

The limitless_cancel_session function works similarly to pg_cancel_backend, but it tries to cancel all backend processes related to the provided distributed session ID by sending a SIGINT (interruption signal).

The input parameter is the following:

The output parameters are the following:

The following example shows how to use the limitless_cancel_session function.

SELECT * FROM rds_aurora.limitless_cancel_session('940CD5C81E3C796B');

 subcluster_id |  pid  | success
---------------+-------+---------
             1 | 26920 | t
(1 row)

The limitless_stat_clear_snapshot function discards the current statistics snapshot or cached information on all nodes.

The following example shows how to use the limitless_stat_clear_snapshot function.

SELECT rds_aurora.limitless_stat_clear_snapshot();

The limitless_stat_database_size function returns the sizes of a database in the DB shard group.

The input parameter is the following:

The output parameters are the following:

The following example shows how to use the limitless_stat_database_size function.

SELECT * FROM rds_aurora.limitless_stat_database_size('postgres_limitless');

 subcluster_id | subcluster_type | db_size
---------------+-----------------+----------
             1 | router          |  8895919
             2 | router          |  8904111
             3 | shard           | 21929391
             4 | shard           | 21913007
             5 | shard           | 21831087
(5 rows)

The limitless_stat_get_snapshot_timestamp function returns the timestamp of the current statistics snapshot, or NULL if no statistics snapshot has been taken. A snapshot is taken the first time cumulative statistics are accessed in a transaction if stats_fetch_consistency is set to snapshot. Returns a consolidated view of snapshot timestamps from all nodes. The subcluster_id and subcluster_type columns show which node the data is from.

The following example shows how to use the limitless_stat_get_snapshot_timestamp function.

SELECT * FROM rds_aurora.limitless_stat_get_snapshot_timestamp();

 subcluster_id | subcluster_type | snapshot_timestamp
---------------+-----------------+--------------------
             1 | router          | 
             2 | router          | 
             3 | shard           | 
             4 | shard           | 
             5 | shard           | 
(5 rows)

The limitless_stat_prepared_xacts function returns information about transactions on all nodes that are currently prepared for two-phase commit. For more information, see pg_prepared_xacts in the PostgreSQL documentation.

The following example shows how to use the limitless_stat_prepared_xacts function.

postgres_limitless=> SELECT * FROM rds_aurora.limitless_stat_prepared_xacts;

 subcluster_id | subcluster_type | transaction_id |             gid              |           prepared            |  owner_id  |    database_id
---------------+-----------------+----------------+------------------------------+-------------------------------+------------+--------------------
 8             | shard           |        5815978 | 7_4599899_postgres_limitless | 2024-09-03 15:51:17.659603+00 | auroraperf | postgres_limitless
 12            | shard           |        4599138 | 7_4599899_postgres_limitless | 2024-09-03 15:51:17.659637+00 | auroraperf | postgres_limitless
(2 rows)

The limitless_stat_relation_sizes function returns the different sizes of a table in the DB shard group.

The input parameters are the following:

The output parameters are the following:

The following example shows how to use the limitless_stat_relation_sizes function (some columns are omitted).

SELECT * FROM rds_aurora.limitless_stat_relation_sizes('public','customers');

 subcluster_id | subcluster_type | main_size | fsm_size | vm_size | toast_size | table_size | total_size
---------------+-----------------+-----------+----------+---------+------------+------------+------------
             1 | router          |         0 |        0 |       0 |          0 |          0 |          0
             2 | router          |         0 |        0 |       0 |          0 |          0 |          0
             3 | shard           |   4169728 |  4177920 | 1392640 |    1392640 |   11132928 |   11132928
             4 | shard           |   4169728 |  4177920 | 1392640 |    1392640 |   11132928 |   11132928
             5 | shard           |   3981312 |  4227072 | 1409024 |    1409024 |   11026432 |   11026432
(5 rows)

The limitless_stat_reset function resets all statistics counters for the current database to zero (0). If track_functions is enabled, the stats_reset column in limitless_stat_database shows the last time statistics were reset for the database. By default, limitless_stat_reset can be run only by a superuser. Other users can be granted permission by using the EXECUTE privilege.

The following example shows how to use the limitless_stat_reset function.

SELECT tup_inserted, tup_deleted FROM pg_stat_database
WHERE datname = 'postgres_limitless';

 tup_inserted | tup_deleted
--------------+-------------
          896 |           0
(1 row)

SELECT rds_aurora.limitless_stat_reset();

limitless_stat_reset
---------------------
(1 row)

SELECT tup_inserted, tup_deleted FROM pg_stat_database
WHERE datname = 'postgres_limitless';

tup_inserted | tup_deleted
-------------+-------------
           0 |           0
(1 row)

The limitless_stat_statements_reset function discards statistics gathered so far by limitless_stat_statements corresponding to the specified username, dbname, distributed_query_id, and queryid parameters. If any of the parameters aren't specified, the default value "" or 0 (invalid) is used for each of them, and the statistics that match with other parameters are reset. If no parameter is specified, or all the specified parameters are "" or 0 (invalid), the function discards all statistics. If all statistics in the limitless_stat_statements view are discarded, the function also resets the statistics in the limitless_stat_statements_info view.

The input parameters are the following:

The following example shows how to use the limitless_stat_statements_reset function to reset all of the statistics gathered by limitless_stat_statements.

SELECT rds_aurora.limitless_stat_statements_reset();

The limitless_stat_system_waits function returns a consolidated view of the wait event data from aurora_stat_system_waits, which reports system wide wait activity in an instance, from all nodes. The subcluster_id and subcluster_type columns show which node the data is from.

The following example shows how to use the limitless_stat_system_waits function.

postgres_limitless=> SELECT *
FROM rds_aurora.limitless_stat_system_waits() lssw, pg_catalog.aurora_stat_wait_event() aswe
WHERE lssw.event_id=aswe.event_id and aswe.event_name='LimitlessTaskScheduler';

 subcluster_id | subcluster_type | type_id | event_id  | waits  |  wait_time   |        event_name
---------------+-----------------+---------+-----------+--------+--------------+------------------------
             1 | router          |      12 | 201326607 | 677068 | 616942216307 | LimitlessTaskScheduler
             2 | router          |      12 | 201326607 | 678586 | 616939897111 | LimitlessTaskScheduler
             3 | shard           |      12 | 201326607 | 756640 | 616965545172 | LimitlessTaskScheduler
             4 | shard           |      12 | 201326607 | 755184 | 616958057620 | LimitlessTaskScheduler
             5 | shard           |      12 | 201326607 | 757522 | 616963183539 | LimitlessTaskScheduler
(5 rows)

The limitless_terminate_session function works similarly to pg_terminate_backend, but it tries to end all backend processes related to the provided distributed session ID by sending a SIGTERM (end signal).

The input parameter is the following:

The output parameters are the following:

The following example shows how to use the limitless_terminate_session function.

SELECT * FROM rds_aurora.limitless_terminate_session('940CD5C81E3C796B');

 subcluster_id |  pid  | success
---------------+-------+---------
             1 | 26920 | t 
(1 row)

The limitless_wait_report function returns the wait event activity over a period of time from all nodes. The subcluster_id and subcluster_type columns show which node the data is from.

The output parameters are the following:

The rest of the columns are the same as in aurora_wait_report.

The following example shows how to use the limitless_wait_report function.

postgres_limitless=> select * from rds_aurora.limitless_wait_report();

 subcluster_id | subcluster_type | type_name | event_name | waits | wait_time | ms_per_wait | waits_per_xact | ms_per_xact
---------------+-----------------+-----------+------------+-------+-----------+-------------+--------------- +-------------
             1 | router          | Client    | ClientRead |    57 | 741550.14 |   13009.652 |           0.19 |    2505.237
             5 | shard           | Client    | ClientRead |    54 | 738897.68 |   13683.290 |           0.18 |    2496.276
             4 | shard           | Client    | ClientRead |    54 | 738859.53 |   13682.584 |           0.18 |    2496.147
             2 | router          | Client    | ClientRead |    53 | 719223.64 |   13570.257 |           0.18 |    2429.810
             3 | shard           | Client    | ClientRead |    54 | 461720.40 |    8550.378 |           0.18 |    1559.86