Expand Up @@ -9,13 +9,13 @@ Introduction PostgreSQL provides information about current wait event of particular process. However, in order to gather descriptive statistics of server behavioruser have to sample current waitevent multiple times. behaviorusers have to sample current waitevents multiple times. `pg_wait_sampling` is an extension for collecting sampling statistics of wait events. The module must be loaded by adding `pg_wait_sampling` to `shared_preload_libraries` in postgresql.conf, because it requires additional shared memory and launches background worker. This means that a server restart shared memory and launchesa background worker. This means that a server restart is needed to add or remove the module. When used with `pg_stat_statements` it is recommended to put `pg_stat_statements` Expand All @@ -25,17 +25,16 @@ utility statements are not rewritten by the former. When `pg_wait_sampling` is enabled, it collects two kinds of statistics. * History of waits events. It's implemented as in-memory ring buffer where samples of each process wait events are written with given (configurable) samples of each process' wait events are written with given (configurable) period. Therefore, for each running process user can see some number of recent samples depending on history size (configurable). Assuming there is a client who periodically read this history and dump it somewhere, user can have continuous history. * Waits profile. It's implemented as in-memory hash table where count of samples are accumulated per each process and each wait event (and each query with `pg_stat_statements`). This hash table can be reset by user request. Assuming there is a client who periodically dumps profile and resets it, user can have statistics of intensivity of wait events among time. recent samples depending on history size (configurable). Assuming there is a client who periodically reads this history and dumps it somewhere, user can have continuous history of wait events. * Waits profile. It's implemented as in-memory hash table where samples are accumulated per each wait event and can be divided by process, wait event, query and other dimensions. This hash table can be reset by user request. Assuming there is a client who periodically dumps profile and resets it, user can have statistics of wait events over time. In combination with `pg_stat_statements` this extension can also provide per query statistics. Expand Down Expand Up @@ -66,10 +65,10 @@ Manual build higher. Before build and install you should ensure following: * PostgreSQL version is 13 or higher. * You have development package of PostgreSQL installed or you built * You have development package of PostgreSQL installed or youhave built PostgreSQL from source. * Your PATH variable is configured so that `pg_config` command available, or set PG_CONFIG variable. PG_CONFIG variable is set . Typical installation procedure may look like this: Expand Down Expand Up @@ -98,53 +97,84 @@ Usage `pg_wait_sampling` interacts with user by set of views and functions. `pg_wait_sampling_current` view – information about current wait events for all processed including background workers. | Column name | Column type | Description | | ----------- | ----------- | ----------------------- | | pid | int4 | Id of process | | event_type | text | Name of wait event type | | event | text | Name of wait event | | queryid | int8 | Id of query | all processes including background workers. | Column name | Column type | Description | | ------------------- | ----------- | --------------------------- | | pid | int4 | Id of process | | event_type | text | Name of wait event type | | event | text | Name of wait event | | queryid | int8 | Id of query | | role_id | int4 | Id of role | | database_id | int4 | Id of database | | parallel_leader_pid | int4 | Id of parallel query leader | | backend_type | text | Name of backend type | | backend_state | text | Name of backend state | | proc_start | timestamptz | Timestamp of process start | | client_addr | text | Client address | | client_hostname | text | Client hostname | | appname | text | Application name | `pg_wait_sampling_get_current(pid int4)` returns the same table for single given process. `pg_wait_sampling_history` view – history of wait events obtained by sampling into in-memory ring buffer. | Column name | Column type | Description | | ----------- | ----------- | ----------------------- | | pid | int4 | Id of process | | ts | timestamptz | Sample timestamp | | event_type | text | Name of wait event type | | event | text | Name of wait event | | queryid | int8 | Id of query | | Column name | Column type | Description | | ------------------- | ----------- | --------------------------- | | pid | int4 | Id of process | | event_type | text | Name of wait event type | | event | text | Name of wait event | | queryid | int8 | Id of query | | role_id | int4 | Id of role | | database_id | int4 | Id of database | | parallel_leader_pid | int4 | Id of parallel query leader | | backend_type | text | Name of backend type | | backend_state | text | Name of backend state | | proc_start | timestamptz | Timestamp of process start | | client_addr | text | Client address | | client_hostname | text | Client hostname | | appname | text | Application name | | ts | timestamptz | Sample timestamp | `pg_wait_sampling_reset_history()` function resets the history. `pg_wait_sampling_profile` view – profile of wait events obtained by sampling into in-memory hash table. | Column name | Column type | Description | | ----------- | ----------- | ----------------------- | | pid | int4 | Id of process | | event_type | text | Name of wait event type | | event | text | Name of wait event | | queryid | int8 | Id of query | | count | text | Count of samples | | Column name | Column type | Description | | ------------------- | ----------- | --------------------------- | | pid | int4 | Id of process | | event_type | text | Name of wait event type | | event | text | Name of wait event | | queryid | int8 | Id of query | | role_id | int4 | Id of role | | database_id | int4 | Id of database | | parallel_leader_pid | int4 | Id of parallel query leader | | backend_type | text | Name of backend type | | backend_state | text | Name of backend state | | proc_start | timestamptz | Timestamp of process start | | client_addr | text | Client address | | client_hostname | text | Client hostname | | appname | text | Application name | | count | int8 | Count of samples | `pg_wait_sampling_reset_profile()` function resets the profile. The work of wait event statistics collector worker is controlled by following GUCs. | Parameter name | Data type | Description | Default value | |----------------------------------| --------- |---------------------------------------------|--------------:| | pg_wait_sampling.history_size | int4 | Size of history in-memory ring buffer | 5000 | | pg_wait_sampling.history_period | int4 | Period for history sampling in milliseconds | 10 | | pg_wait_sampling.profile_period | int4 | Period for profile sampling in milliseconds | 10 | | pg_wait_sampling.profile_pid | bool | Whether profile should be per pid | true | | pg_wait_sampling.profile_queries | enum | Whether profile should be per query | top | | pg_wait_sampling.sample_cpu | bool | Whether on CPU backends should be sampled | true | | Parameter name | Data type | Description | Default value | |-------------------------------------| --------- |---------------------------------------------|----------------------------------------------| | pg_wait_sampling.history_size | int4 | Size of history in-memory ring buffer | 5000 | | pg_wait_sampling.history_period | int4 | Period for history sampling in milliseconds | 10 | | pg_wait_sampling.profile_period | int4 | Period for profile sampling in milliseconds | 10 | | pg_wait_sampling.profile_pid | bool | Whether profile should be per pid | true | | pg_wait_sampling.profile_queries | enum | Whether profile should be per query | top | | pg_wait_sampling.sample_cpu | bool | Whether on CPU backends should be sampled | true | | pg_wait_sampling.history_dimensions | text | Additional columns in extended history view | 'pid, wait_event_type, wait_event, query_id' | | pg_wait_sampling.profile_dimensions | text | Additional columns in extended profile view | 'pid, wait_event_type, wait_event, query_id' | If `pg_wait_sampling.profile_pid` is set to false, sampling profile wouldn't be collected in per-process manner. In this case the value of pid could would Expand All @@ -158,10 +188,28 @@ If `pg_wait_sampling.sample_cpu` is set to true then processes that are not waiting on anything are also sampled. The wait event columns for such processes will be NULL. `pg_wait_sampling.history_dimenstions` and `pg_wait_sampling.profile_dimensions` determine what additional columns will be sampled in `history/profile_extended` views. Possible values are `all`, `pid`, `wait_event_type`, `wait_event`, `query_id`, `role_id`, `database_id`, `parallel_leader_pid`, `backend_type`, `backend_state`, `backend_start_time`, `client_addr`, `client_hostname`, `appname` and any combination of column names. `all` cannot be used together with any other values and must be used alone. > [!WARNING] > Turning on any of the following columns: `backend_type`, `backend_state`, > `backend_start_time`, `client_addr`, `client_hostname`, `appname` will reduce > performance compared to sampling none of those due to the need to look into > BackendStatusTable. This is especially noticeable with PostgreSQL 13-16 Values of these GUC variables can be changed only in config file or with ALTER SYSTEM. Then you need to reload server's configuration (such as with pg_reload_conf function) Then you need to reload server's configuration (such as with` pg_reload_conf` function) for changes to take effect. > [!WARNING] > When using `pg_reload_conf` you also need to invoke `pg_wait_sampling_reset_history()` > and `pg_wait_sampling_reset_profile()` for correct application of new dimensions See [PostgreSQL documentation](http://www.postgresql.org/docs/devel/static/monitoring-stats.html#WAIT-EVENT-TABLE) for list of possible wait events. Expand All @@ -170,7 +218,7 @@ Contribution ------------ Please, notice, that `pg_wait_sampling` is still under development and while it's stable and tested, it maycontains some bugs. Don't hesitate to raise it's stable and tested, it maycontain some bugs. Don't hesitate to raise [issues at github](https://github.com/postgrespro/pg_wait_sampling/issues) with your bug reports. Expand Down