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pg_stat_monitor doc review

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Anastasia Alexandrova
2020-11-26 17:01:14 +02:00
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docs/USER_GUIDE.md
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## User Guide
# User Guide
Create the extension using the ``CREATE EXTENSION`` command.
This document describes the configuration, key features and usage of ``pg_stat_monitor`` extension and compares it with ``pg_stat_statements``.
For how to install and set up ``pg_stat_monitor``, see [README](https://github.com/percona/pg_stat_monitor/blob/master/README.md).
After you've installed and enabled ``pg_stat_monitor``, create the ``pg_stat_monitor`` extension using the ``CREATE EXTENSION`` command.
```sql
CREATE EXTENSION pg_stat_monitor;
@@ -27,7 +31,7 @@ SELECT * FROM pg_stat_monitor_settings;
```
Some configuration parameters require the server restart and should be set before the server startup. These must be set in the ``postgresql.conf`` file. Other parameters do not require server restart and can be set permanently either in the ``postgresql.conf`` or from the client (``psql``).
The table below shows set up options for each configuration parameter and whether the server restart is required to apply its value:
The table below shows set up options for each configuration parameter and whether the server restart is required to apply the parameter's value:
| Parameter Name                                |  postgresql.conf   | SET | ALTER SYSTEM SET  |  server restart   | configuration reload
@@ -59,9 +63,10 @@ The table below shows set up options for each configuration parameter and whethe
### Usage
pg_stat_monitor extension contains a view called pg_stat_monitor, which contains all the monitoring information. Following is the list of columns in pg_stat_monitor.
pg_stat_monitor extension contains a view called pg_stat_monitor, which contains all the monitoring information. Find the list of columns in pg_stat_monitor view in the following table. The table also shows whether a particular column is available in pg_stat_statements.
|      Column        |           Type           | pg_stat_monitor      | pg_stat_statments
|      Column        |           Type           | pg_stat_monitor      | pg_stat_statements
|--------------------|--------------------------|----------------------|------------------
 bucket              | integer                  | :heavy_check_mark:  | :x:
 bucket_start_time   | timestamp with time zone | :heavy_check_mark:  | :x:
@@ -105,10 +110,11 @@ pg_stat_monitor extension contains a view called pg_stat_monitor, which contains
 cpu_user_time       | double precision         | :heavy_check_mark:  | :x:
 cpu_sys_time        | double precision         | :heavy_check_mark:  | :x:
Here are some key features of pg_stat_monitor.
The following are some key features of pg_stat_monitor and usage examples.
#### Buckets
pg_stat_monitor collects and aggregates data on a bucket basis. The size of a bucket and the number of buckets should be configured using GUC (Grand Unified Configuration). When a bucket time elapses, pg_stat_monitor resets all the statistics and switches to the next bucket. After the last bucket elapses, pg_stat_monitor goes back to the first bucket. All the data on the first bucket will vanish; therefore, users must read the buckets before that to not lose the data.
**`bucket`**: Accumulates the statistics per bucket. All the information and aggregate reset for each bucket. The bucket will be a number showing the number of buckets for which this record belongs.
@@ -126,7 +132,7 @@ SELECT bucket, bucket_start_time, query FROM pg_stat_monitor;
#### Query Information
**`userid`**: An ID of the user to whom that query belongs. pg_stat_monitor is used to collect queries from all the users; therefore, `userid` is used to segregate the queries based on different users.
**`userid`**: An ID of the user to whom that query belongs. pg_stat_monitor collects queries from all the users and uses the `userid` to segregate the queries based on different users.
**`dbid`**: The database ID of the query. pg_stat_monitor accumulates queries from all the databases; therefore, this column is used to identify the database.
@@ -137,7 +143,7 @@ SELECT bucket, bucket_start_time, query FROM pg_stat_monitor;
**`calls`**: Number of calls of that particular query.
##### Example 1: Shows the userid, dbid, unique queryid hash, query, and the total number of calls or that query.
##### Example 1: Shows the userid, dbid, unique queryid hash, query, and the total number of calls of that query.
```sql
SELECT userid,  dbid, queryid, substr(query,0, 50) AS query, calls FROM pg_stat_monitor;
 userid | dbid  |     queryid      |                       query                       | calls
@@ -163,7 +169,7 @@ SELECT userid,  dbid, queryid, substr(query,0, 50) AS query, calls FROM pg_stat
(18 rows)
```
##### Example 2: Shows the different usernames for the query.
##### Example 2: Shows different usernames for the query.
```
SELECT userid::regrole, datname, substr(query,0, 50) AS query, calls from pg_stat_monitor, pg_database WHERE dbid = oid;
@@ -177,7 +183,7 @@ SELECT userid::regrole, datname, substr(query,0, 50) AS query, calls from pg_sta
(5 rows)
```
##### Example 3: Shows the different database involved in the queries.
##### Example 3: Shows the different databases involved in the queries.
```
SELECT userid::regrole, datname, substr(query,0, 50) as query, calls from pg_stat_monitor, pg_database WHERE dbid = oid;
@@ -213,7 +219,7 @@ SELECT application_name, query FROM pg_stat_monitor;
#### Error Messages / Error Codes and Error Level
**`elevel`**, **`sqlcode`**,**`message`**,: error level / sql code and  log/warning/error message
**`elevel`**, **`sqlcode`**,**`message`**,: error level / sql code and  log/warning/ error message
```sql
SELECT substr(query,0,50) AS query, decode_error_level(elevel) AS elevel,sqlcode, calls, substr(message,0,50) message