Authors:

avatar of Roy Golan

Roy Golan

Feature pages are design documents that developers have created while collaborating on oVirt.

Most of them are outdated, but provide historical design context.

They are not user documentation and should not be treated as such.

Documentation is available here.

Engine Vacuum

Description

This page describes the engine-vacuum cli tool and the vacuum setup-plugin that uses it.

Motivation

“PostgreSQL databases require periodic maintenance known as vacuuming. For many installations, it is sufficient to let vacuuming be performed by the autovacuum daemon”

Apart from updating the tables and removing garbage from the tables, full vacuum is the only vacuum operation that can reclaim disk space back to the operating system. If the engine db is falling behind in collecting garbage,(autovacuum doesn’t perfom optimally) we will see disk usage growth in time as a result.

The engine-vacuum tool is a wrapper around postgres commands and is aimed to ease Vacuum maintenance actions on the DB, and can be used easily and securely, as they reuse the setup credentials to authenticate against the engine db. The tool is being used by an engine-setup plugin and act as a maintenance task, taking advantage of the downtime period when updating the engine. The tool can be used just as well by cron, script or just manual invocation and it covers most of the functionality of the vacuum commands.

Scope

This page covers the tool itself, and the engine-setup plugin that was created to use it.

Not covered - Vacuum design and functionality. See the references section to read about vacuum.

Synopsis

engine-vacuum

  engine-vacuum [OPTION]...

Located under /bin/engine-vacuum, invoking this can perform vacuum, vacuum full and analyze against the installed engine db, optionally specifying the tables, without needing to specifying the engine db, user and password.

engine-vacuum --help

  -a          - run analyze, update optimizer statistics
  -A          - run analyze only, only update optimizer stats, no vacuum
  -f          - do full vacuuming
  -t          - vacuum specific table
  -v          - verbose output
  -h          - print this usage message

Examples

Run vacuum only:

engine-vacuum

Run vacuum analyze:

engine-vacuum -a

Only update optimizer stats, no vacuum:

engine-vacuum -A

Run vacuum full, and verbose for more output:

engine-vacuum -f -v

Run vacuum full, verbose on vm_dynamic and vds_dynamic tables only:

engine-vacuum -f -v -t vm_dynamic -t vds_dynamic

Vacuum setup plugin

During an execution of engine-setup, excluding new installation, at the customization stage, the setup will raise a dialog, asking to perform full vacuum:

$ engine-setup
...
[ INFO  ] Stage: Environment customization
...
          Perform full vacuum on the engine database engine@localhost?
          This operation may take a while depending on this setup health and the
          configuration of the db vacuum process.
          See https://www.postgresql.org/docs/9.2/static/sql-vacuum.html
          (Yes, No) [No]:

Choosing [Yes], will invoke vacuum full verbose on the engine db by invoking engine-vacuum -f -v and by setting /tmp/{tmpdir}/.pgpass - See pgpass documantation.

  • Default value: No (does nothing)
  • Output: to the install log, small elapsed time summary to the console
  • Answer file entry: OVESETUP_DB/engineVacuumFull=bool:False
  • Fail install on error: Yes, output will go to the installation log

Security

The credentials of the user, engine db and password are taken from /etc/ovirt-engine/engine.conf.d/10-setup-database and passed using .pgpass file thus not used as a command argument and not in risk to go into history, log or similar. See pgpass documentation for more details.

TODO

  • Try to give a rough estimation of how long this is going to take. We can count the dead rows and at least provide the size of amount of bytes to delete.
select relname,n_dead_tup from pg_stat_user_tables order by n_dead_tup desc;

References