Extensions
- pg_stat_kcache 2.0.2
- An extension gathering CPU and disk acess statistics
README
Contents
pg_stat_kcache
Features
Gathers statistics about real reads and writes done by the filesystem layer. It is provided in the form of an extension for PostgreSQL >= 9.4., and requires pg_stat_statements extension to be installed. PostgreSQL 9.4 or more is required as previous version of provided pg_stat_statements didn't expose the queryid field.
Installation
Compiling
The module can be built using the standard PGXS infrastructure. For this to work, the pg_config program must be available in your $PATH. Instruction to install follows:
git clone https://github.com/dalibo/pg_stat_kcache.git cd pg_stat_kcache make make install
PostgreSQL setup
The extension is now available. But, as it requires some shared memory to hold its counters, the module must be loaded at PostgreSQL startup. Thus, you must add the module to shared_preload_libraries in your postgresql.conf. You need a server restart to take the change into account.
Add the following parameters into you postgresql.conf:
# postgresql.conf shared_preload_libraries = 'pg_stat_kcache'
Once your PostgreSQL cluster is restarted, you can install the extension in every database where you need to access the statistics:
mydb=# CREATE EXTENSION pg_stat_kcache;
Usage
pg_stat_kcache create several objects.
pg_stat_kcache view
Name | Type | Description |
---|---|---|
datname | name | Name of the database |
reads | bigint | Number of blocks read by the filesystem layer |
reads_blks | bigint | Number of 8K blocks read by the filesystem layer |
writes | bigint | Number of blocks written by the filesystem layer |
writes_blks | bigint | Number of 8K blocks written by the filesystem layer |
user_time | double precision | User CPU time used |
system_time | double precision | System CPU time used |
pg_stat_kcache_detail view
Name | Type | Description | |
---|---|---|---|
query | text | Query text | |
datname | name | Database name | |
rolname | name | Role name | |
reads | bigint | Number of bytes read by the filesystem layer | |
reads_blks | bigint | Number of 8K blocks read by the filesystem layer | |
writes | bigint | Number of bytes written by the filesystem layer | |
writes_blks | bigint | Number of 8K blocks written by the filesystem layer | ||
user_time | double precision | User CPU time used | ||
system_time | double precision | System CPU time used | ||
pg_stat_kcache_reset function
Resets the statistics gathered by pg_stat_kcache. Can be called by superusers:
pg_stat_kcache_reset()
pg_stat_kcache function
This function is a set-returning functions that dumps the containt of the counters of the shared memory structure. This function is used by the pg_stat_kcache view. The function can be called by any user:
SELECT * FROM pg_stat_kcache();
It provides the following columns:
Name | Type | Description | |||
---|---|---|---|---|
queryid | bigint | pg_stat_statements' query identifier | |||
userid | oid | Database OID | ||
dbid | oid | Database OID | ||
reads | bigint | Number of bytes read by the filesystem layer | ||
writes | bigint | Number of bytes written by the filesystem layer | |||
user_time | double precision | User CPU time used | |||
system_time | double precision | System CPU time use | ||
Bugs and limitations
No known bugs.
We assume that a kernel block is 512 bytes. This is true for Linux, but may not be the case for another Unix implementation.
See: http://lkml.indiana.edu/hypermail/linux/kernel/0703.2/0937.html
Authors
pg_stat_kcache is an original development from Thomas Reiss, with large portions of code inspired from pg_stat_plans. Julien Rouhaud also contributed some parts of the extension.
Thanks goes to Peter Geoghegan for providing much inspiration with pg_stat_plans so we could write this extension quite straightforward.
License
pg_stat_kcache is free software distributed under the PostgreSQL license.
Copyright (c) 2014, dalibo.