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81 lines
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81 lines
3.9 KiB
Plaintext
pg_autovacuum README
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pg_autovacuum is a libpq client program that monitors all the databases of a
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postgresql server. It uses the stats collector to monitor insert, update and
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delete activity. When an individual table exceeds it's insert or delete
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threshold (more detail on thresholds below) then that table is vacuumed or
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analyzed. This allows postgresql to keep the fsm and table statistics up to
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date without having to schedule periodic vacuums with cron regardless of need.
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The primary benefit of pg_autovacuum is that the FSM and table statistic information
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are updated as needed. When a table is actively changed pg_autovacuum performs the
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necessary vacuums and analyzes, when a table is inactive, no cycles are wasted
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performing vacuums and analyzes that are not needed.
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A secondary benefit of pg_autovacuum is that it guarantees that a database wide
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vacuum is performed prior to xid wraparound. This is important as failing to do
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so can result in major data loss.
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INSTALL:
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To use pg_autovacuum, uncompress the tar.gz into the contrib directory and modify the
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contrib/Makefile to include the pg_autovacuum directory. pg_autovacuum will then be made as
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part of the standard postgresql install.
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make sure that the folowing are set in postgresql.conf
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stats_start_collector = true
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stats_row_level = true
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start up the postmaster
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then, just execute the pg_autovacuum executable.
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Command line arguments:
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pg_autovacuum has the following optional arguments:
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-d debug: 0 silent, 1 basic info, 2 more debug info, etc...
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-s sleep base value: see "Sleeping" below.
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-S sleep scaling factor: see "Sleeping" below.
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-t tuple base threshold: see Vacuuming.
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-T tuple scaling factor: see Vacuuming.
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-U username: Username pg_autovacuum will use to connect with, if not specified the
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current username is used
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-P password: Password pg_autovacuum will use to connect with.
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-H host: host name or IP to connect too.
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-p port: port used for connection.
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-h help: list of command line options.
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All arguments have default values defined in pg_autovacuum.h. At the time of this
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writing they are:
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#define AUTOVACUUM_DEBUG 1
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#define BASETHRESHOLD 100
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#define SCALINGFACTOR 2
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#define SLEEPVALUE 3
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#define SLEEPSCALINGFACTOR 2
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#define UPDATE_INTERVAL 2
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Vacuum and Analyze:
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pg_autovacuum performes either a vacuums analyze or just analyze depending on the table activity.
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If the number of (inserts + updates) > insertThreshold, then an only an analyze is performed.
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If the number of (deletes + updates ) > deleteThreshold, then a vacuum analyze is performed.
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deleteThreshold is equal to: tuple_base_value + (tuple_scaling_factor * "number of tuples in the table")
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insertThreshold is equal to: 0.5 * tuple_base_value + (tuple_scaling_factor * "number of tuples in the table")
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The insertThreshold is half the deleteThreshold because it's a much lighter operation (approx 5%-10% of vacuum),
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so running it more often costs us little in performance degredation.
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Sleeping:
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pg_autovacuum sleeps after it is done checking all the databases. It does this so as
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to limit the amount of system resources it consumes. This also allows the system
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administrator to configure pg_autovacuum to be more or less aggressive. Reducing the
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sleep time will cause pg_autovacuum to respond more quickly to changes, be they database
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addition / removal, table addition / removal, or just normal table activity. However,
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setting these values to high can have a negative net effect on the server. If a table
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gets vacuumed 5 times during the course of a large update, it might take much longer
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than if it was vacuumed only once.
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The total time it sleeps is equal to:
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base_sleep_value + sleep_scaling_factor * "duration of the previous loop"
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What it monitors:
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pg_autovacuum dynamically generates a list of databases and tables to monitor, in
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addition it will dynamically add and remove databases and tables that are
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removed from the database server while pg_autovacuum is running.
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