# LWLock:pg\$1stat\$1statements
The LWLock:pg\$1stat\$1statements wait event occurs when the `pg_stat_statements` extension takes an exclusive lock on the hash table that tracks SQL statements. This happens in the following scenarios:
+ When the number of tracked statements reaches the configured `pg_stat_statements.max` parameter value and there is a need to make room for more entries, the extension performs a sort on the number of calls, removes the 5% of the least-executed statements, and re-populates the hash with the remaining entries.
+ When `pg_stat_statements` performs a `garbage collection` operation to the `pgss_query_texts.stat` file on disk and rewrites the file.
**Topics**
+ [
## Supported engine versions
](#apg-rpg-lwlockpgstat.supported)
+ [
## Context
](#apg-rpg-lwlockpgstat.context)
+ [
## Likely causes of increased waits
](#apg-rpg-lwlockpgstat.causes)
+ [
## Actions
](#apg-rpg-lwlockpgstat.actions)
## Supported engine versions
This wait event information is supported for all versions of Aurora PostgreSQL.
## Context
**Understanding the pg\$1stat\$1statements extension** – The pg\$1stat\$1statements extension tracks SQL statement execution statistics in a hash table. The extension tracks SQL statements up to the limit defined by the `pg_stat_statements.max` parameter. This parameter determines the maximum number of statements that can be tracked which corresponds to the maximum number of rows in the pg\$1stat\$1statements view.
**Statement statistics persistence** – The extension persists statement statistics across instance restarts by:
+ Writing data to a file named pg\$1stat\$1statements.stat
+ Using the pg\$1stat\$1statements.save parameter to control persistence behavior
When pg\$1stat\$1statements.save is set to:
+ on (default): Statistics are saved at shutdown and reloaded at server start
+ off: Statistics are neither saved at shutdown nor reloaded at server start
**Query text storage** – The extension stores the text of tracked queries in a file named `pgss_query_texts.stat`. This file can grow to double the average size of all tracked SQL statements before garbage collection occurs. The extension requires an exclusive lock on the hash table during cleanup operations and rewrite `pgss_query_texts.stat` file.
**Statement deallocation process** – When the number of tracked statements reaches the `pg_stat_statements.max` limit and new statements need to be tracked, the extension:
+ Takes an exclusive lock (LWLock:pg\$1stat\$1statements) on the hash table.
+ Loads existing data into local memory.
+ Performs a quicksort based on the number of calls.
+ Removes the least-called statements (bottom 5%).
+ Re-populates the hash table with the remaining entries.
**Monitoring statement deallocation** – In PostgreSQL 14 and later, you can monitor statement deallocation using the pg\$1stat\$1statements\$1info view. This view includes a dealloc column that shows how many times statements were deallocated to make room for new ones
If the deallocation of statements occurs frequently, it will lead to more frequent garbage collection of the `pgss_query_texts.stat` file on disk.
## Likely causes of increased waits
The typical causes of increased `LWLock:pg_stat_statements` waits include:
+ An increase in the number of unique queries used by the application.
+ The `pg_stat_statements.max` parameter value being small compared to the number of unique queries being used.
## Actions
We recommend different actions depending on the causes of your wait event. You might identify `LWLock:pg_stat_statements` events by using Amazon RDS Performance Insights or by querying the view `pg_stat_activity`.
Adjust the following `pg_stat_statements` parameters to control tracking behavior and reduce LWLock:pg\$1stat\$1 statements wait events.
**Topics**
+ [
### Disable pg\$1stat\$1statements.track parameter
](#apg-rpg-lwlockpgstat.actions.disabletrack)
+ [
### Increase pg\$1stat\$1statements.max parameter
](#apg-rpg-lwlockpgstat.actions.increasemax)
+ [
### Disable pg\$1stat\$1statements.track\$1utility parameter
](#apg-rpg-lwlockpgstat.actions.disableutility)
### Disable pg\$1stat\$1statements.track parameter
If the LWLock:pg\$1stat\$1statements wait event is adversely impacting database performance, and a rapid solution is required before further analysis of the `pg_stat_statements` view to identify the root cause, the `pg_stat_statements.track` parameter can be disabled by setting it to `none`. This will disable the collection of statement statistics.
### Increase pg\$1stat\$1statements.max parameter
To reduce deallocation and minimize garbage collection of the `pgss_query_texts.stat` file on disk, increase the value of the `pg_stat_statements.max` parameter. The default value is `5,000`.
**Note**
The `pg_stat_statements.max` parameter is static. You must restart your DB instance to apply any changes to this parameter.
### Disable pg\$1stat\$1statements.track\$1utility parameter
You can analyze the pg\$1stat\$1statements view to determine which utility commands are consuming the most resources tracked by `pg_stat_statements`.
The `pg_stat_statements.track_utility` parameter controls whether the module tracks utility commands, which include all commands except SELECT, INSERT, UPDATE, DELETE, and MERGE. By default, this parameter is set to `on`.
For example, when your application uses many savepoint queries, which are inherently unique, it can increase statement deallocation. To address this, you can disable the `pg_stat_statements.track_utility` parameter to stop `pg_stat_statements` from tracking savepoint queries.
**Note**
The `pg_stat_statements.track_utility` parameter is a dynamic parameter. You can change its value without restarting your database instance.
**Example of unique save point queries in pg\$1stat\$1statements**
```
query | queryid
-------------------------------------------------+---------------------
SAVEPOINT JDBC_SAVEPOINT_495701 | -7249565344517699703
SAVEPOINT JDBC_SAVEPOINT_1320 | -1572997038849006629
SAVEPOINT JDBC_SAVEPOINT_26739 | 54791337410474486
SAVEPOINT JDBC_SAVEPOINT_1294466 | 8170064357463507593
ROLLBACK TO SAVEPOINT JDBC_SAVEPOINT_65016 | -33608214779996400
SAVEPOINT JDBC_SAVEPOINT_14185 | -2175035613806809562
SAVEPOINT JDBC_SAVEPOINT_45837 | -6201592986750645383
SAVEPOINT JDBC_SAVEPOINT_1324 | 6388797791882029332
```
PostgreSQL 17 introduces several enhancements for utility command tracking:
+ Savepoint names are now displayed as constants.
+ Global Transaction IDs (GIDs) of two-phase commit commands are now displayed as constants.
+ Names of DEALLOCATE statements are shown as constants.
+ CALL parameters are now displayed as constants.