databases associated with a postgresql server. It uses the stats

When a table exceeds its insert or delete threshold (more detail

on thresholds below) then that table will be vacuumed or analyzed.

This allows postgresql to keep the fsm and table statistics up to

date, and eliminates the need to schedule periodic vacuums.

statistic information are updated as needed. When a table is actively

changing, pg_autovacuum will perform the necessary vacuums and

analyzes, whereas if a table remains static, no cycles will be wasted

performing unnecessary vacuums/analyzes.

database wide vacuum is performed prior to xid wraparound. This is an

data loss.

pg_autovacuum has been tested under Redhat Linux (by me) and Solaris (by

Christopher B. Browne) and all known bugs have been resolved. Please report

any problems to the hackers list.

pg_autovacuum does not get started automatically by either the postmaster or

by pg_ctl. Along the sames lines, when the postmaster exits no one tells

pg_autovacuum. The result is that at the start of the next loop,

pg_autovacuum fails to connect to the server and exits. Any time it fails

to connect pg_autovacuum exits.

pg_autovacuum requires that the stats system be enabled and reporting row

level stats. The overhead of the stats system has been shown to be

significant under certain workloads. For instance a tight loop of queries

performing "select 1" was nearly 30% slower with stats enabled. However,

in practice with more realistic workloads, the stats system overhead is

usually nominal.

As of postgresql v7.4 pg_autovacuum is included in the main source tree

under contrib. Therefore you just make && make install (similar to most other

contrib modules) and it will be installed for you.

If you are using an earlier version of postgresql just uncompress the tar.gz

into the contrib directory and modify the contrib/Makefile to include the pg_autovacuum

directory. pg_autovacuum will then be made as part of the standard

postgresql install.

make sure that the folowing are set in postgresql.conf

start up the postmaster, then execute the pg_autovacuum executable.

-D dameonize: Detach from tty and run in background.

-H host: host name or IP to connect too.

All arguments have default values defined in pg_autovacuum.h. At the

time of writing they are:

-a 500 (half of -v is not specified)

-A 1 (half of -v is not specified)

pg_autovacuum performs either a vacuum analyze or just analyze depending

on the quantity and type of table activity (insert, update, or delete):

- If the number of (deletes + updates ) > VacuumThreshold, then a

represents a much less expensive operation (approx 5%-10% of vacuum), and

running it more often should not substantially degrade system performance.

resources it consumes. This also allows the system administrator to

On the other hand, setting pg_autovaccum to sleep values to agressivly

(for too short a period of time) can have a negative effect on server

performance. If a table gets vacuumed 5 times during the course of a

large update, this is likely to take much longer than if the table was

vacuumed only once, at the end.

"pg_vacuum -s 1" means pg_autovacuum could poll the database upto 60 times

minute. In a system with large tables where vacuums may run for several

minutes, longer times between vacuums are likely to be appropriate.

pg_autovacuum dynamically generates a list of all databases and tables that

exist on the server. It will dynamically add and remove databases and

tables that are removed from the database server while pg_autovacuum is

running. Overhead is fairly small per object. For example: 10 databases

with 10 tables each appears to less than 10k of memory on my Linux box.

res = send_query(query_table_stats(dbi), dbi);

sprintf(logbuffer, " relfilenode: %i", tbl->relfilenode);

char *

query_table_stats(db_info * dbi)

{

if (!strcmp(dbi->dbname, "template1")) /* Use template1 to

return (char *) TABLE_STATS_ALL;

else

return (char *) TABLE_STATS_USER;

}

res = send_query(query_table_stats(dbs), dbs); /* Get an updated

snprintf(buf, sizeof(buf), "VACUUM ANALYZE \"%s\"", tbl->table_name);

snprintf(buf, sizeof(buf), "ANALYZE \"%s\"", tbl->table_name);

#define TABLE_STATS_ALL "select a.relfilenode,a.relname,a.relnamespace,a.relpages,a.reltuples,b.schemaname,b.n_tup_ins,b.n_tup_upd,b.n_tup_del from pg_class a, pg_stat_all_tables b where a.relfilenode=b.relid"

static char *query_table_stats(db_info * dbi);