Adds pg_stat_progress_vacuum collector

[ianbibby]

This pull request adds a new collector that exposes metrics from pg_stat_progress_vacuum, enabling visibility into in-progress VACUUM operations. The collected metrics include:

• Current phase of the vacuum (folllowing the State Set pattern)
• Heap blocks scanned / vacuumed
• Index vacuum cycle count
• Dead tuple counts and limits

This collector queries the underlying function pg_stat_get_progress_info('VACUUM'::text) directly rather than using the pg_stat_progress_vacuum view.

Testing

• Added unit tests, following the same structure as existing collectors (e.g. pg_stat_user_tables_test.go)
• Manually tested against live PostgreSQL instances with vacuum activity, using controlled workloads to generate observable vacuum progress
• Verified that metrics appear and update correctly on the Prometheus /metrics endpoint

Example output:

# HELP pg_stat_progress_vacuum_heap_blks Total number of heap blocks in the table being vacuumed.
# TYPE pg_stat_progress_vacuum_heap_blks gauge
pg_stat_progress_vacuum_heap_blks{datname="postgres",relname="foo"} 638708
# HELP pg_stat_progress_vacuum_heap_blks_scanned Number of heap blocks scanned so far.
# TYPE pg_stat_progress_vacuum_heap_blks_scanned gauge
pg_stat_progress_vacuum_heap_blks_scanned{datname="postgres",relname="foo"} 8448
# HELP pg_stat_progress_vacuum_heap_blks_vacuumed Number of heap blocks vacuumed so far.
# TYPE pg_stat_progress_vacuum_heap_blks_vacuumed gauge
pg_stat_progress_vacuum_heap_blks_vacuumed{datname="postgres",relname="foo"} 0
# HELP pg_stat_progress_vacuum_index_vacuums Number of completed index vacuum cycles.
# TYPE pg_stat_progress_vacuum_index_vacuums gauge
pg_stat_progress_vacuum_index_vacuums{datname="postgres",relname="foo"} 0
# HELP pg_stat_progress_vacuum_max_dead_tuples Maximum number of dead tuples that can be stored before cleanup is performed.
# TYPE pg_stat_progress_vacuum_max_dead_tuples gauge
pg_stat_progress_vacuum_max_dead_tuples{datname="postgres",relname="foo"} 1.1184809e+07
# HELP pg_stat_progress_vacuum_num_dead_tuples Current number of dead tuples found so far.
# TYPE pg_stat_progress_vacuum_num_dead_tuples gauge
pg_stat_progress_vacuum_num_dead_tuples{datname="postgres",relname="foo"} 228096
# HELP pg_stat_progress_vacuum_phase Current vacuum phase (1 = active, 0 = inactive). Label 'phase' is human-readable.
# TYPE pg_stat_progress_vacuum_phase gauge
pg_stat_progress_vacuum_phase{datname="postgres",phase="cleaning up indexes",relname="foo"} 0
pg_stat_progress_vacuum_phase{datname="postgres",phase="initializing",relname="foo"} 0
pg_stat_progress_vacuum_phase{datname="postgres",phase="performing final cleanup",relname="foo"} 0
pg_stat_progress_vacuum_phase{datname="postgres",phase="scanning heap",relname="foo"} 1
pg_stat_progress_vacuum_phase{datname="postgres",phase="truncating heap",relname="foo"} 0
pg_stat_progress_vacuum_phase{datname="postgres",phase="vacuuming heap",relname="foo"} 0
pg_stat_progress_vacuum_phase{datname="postgres",phase="vacuuming indexes",relname="foo"} 0

Compatibility

• This collector supports PostgreSQL versions 9.6 through 16.
• The param mappings used from pg_stat_get_progress_info are consistent across these versions

Postgres 17 support

PostgreSQL 17 introduces breaking changes (pgpedia):

• max_dead_tuples and num_dead_tuples were removed
• Replaced by max_dead_tuple_bytes, dead_tuple_bytes, and num_dead_item_ids

This collector is not currently compatible with Postgres 17, but this is a known limitation. A future update can address this by adjusting param mappings based on the server version.

[SuperQ]

A couple of minor nits, and one feature suggestion.

Otherwise, looking good.

[SuperQ]

This needs a DCO sign-off. You can use git commit -s --amend to add it.

[SuperQ]

What do you think about making this one enabled by default. Are vacuum stats useful enough for most users?

[ianbibby]

I think enabling this by default is acceptable here. I'll make it so.

[ianbibby]

This is done.

[SuperQ]

LGTM