Optimizing, monitoring, and troubleshooting VACUUM operations in PostgreSQL
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This document describes the fundamentals of the VACUUM operation in
PostgreSQL
databases. It also describes the mechanisms to monitor and tune the database
engine that maintains the health of database instances.
PostgreSQL uses a snapshot-based concurrency protocol that creates multiple
versions of data rows while modifying the data. These data row versions are used
to read a visible version of the data using a computed snapshot without
acquiring read-lock on the data row. PostgreSQL maintains transaction IDs
(inserted and deleted transaction IDs) for every row of data and uses the
transaction IDs along with the computed snapshot to determine the visibility of
the row. As the data keeps growing due to old versions of data, the time taken
to scan the data (table scan or index scan) increases. To optimize the response
time of the scan operation and to use space efficiently, you need to reclaim the
versions and the metadata (for example, transaction ID) that is used to maintain
the versions.
The VACUUM operation reclaims the deleted versions (garbage collection) and
transaction IDs (freeze transaction ID). The VACUUM operation operates on data
in different modes with different levels of data availability. Freezing
transaction IDs is crucial to the health of the database system because the
system blocks writers whenever the used transaction ID space enters reserved
space.
The autovacuum jobs that you configure constantly try to reclaim the
transaction ID, but they can fail. This failure is either due to insufficient
configuration or because the creation rate for transaction IDs is so high that
the autovacuum job cannot catch up with workload. The purpose of this document
is to show how to use the VACUUM operations along with the mechanisms to tune
and monitor different aspects of VACUUM operations.
[[["Easy to understand","easyToUnderstand","thumb-up"],["Solved my problem","solvedMyProblem","thumb-up"],["Other","otherUp","thumb-up"]],[["Hard to understand","hardToUnderstand","thumb-down"],["Incorrect information or sample code","incorrectInformationOrSampleCode","thumb-down"],["Missing the information/samples I need","missingTheInformationSamplesINeed","thumb-down"],["Other","otherDown","thumb-down"]],["Last updated 2025-09-03 UTC."],[],[],null,["# Optimizing, monitoring, and troubleshooting VACUUM operations in PostgreSQL\n\nThis document describes the fundamentals of the `VACUUM` operation in\n[PostgreSQL](https://www.postgresql.org/)\ndatabases. It also describes the mechanisms to monitor and tune the database\nengine that maintains the health of database instances.\n\nPostgreSQL uses a snapshot-based concurrency protocol that creates multiple\nversions of data rows while modifying the data. These data row versions are used\nto read a visible version of the data using a computed snapshot without\nacquiring read-lock on the data row. PostgreSQL maintains transaction IDs\n(inserted and deleted transaction IDs) for every row of data and uses the\ntransaction IDs along with the computed snapshot to determine the visibility of\nthe row. As the data keeps growing due to old versions of data, the time taken\nto scan the data (table scan or index scan) increases. To optimize the response\ntime of the scan operation and to use space efficiently, you need to reclaim the\nversions and the metadata (for example, transaction ID) that is used to maintain\nthe versions.\n\nThe `VACUUM` operation reclaims the deleted versions (garbage collection) and\ntransaction IDs (freeze transaction ID). The `VACUUM` operation operates on data\nin different modes with different levels of data availability. Freezing\ntransaction IDs is crucial to the health of the database system because the\nsystem blocks writers whenever the used transaction ID space enters reserved\nspace.\n\nThe `autovacuum` jobs that you configure constantly try to reclaim the\ntransaction ID, but they can fail. This failure is either due to insufficient\nconfiguration or because the creation rate for transaction IDs is so high that\nthe `autovacuum` job cannot catch up with workload. The purpose of this document\nis to show how to use the `VACUUM` operations along with the mechanisms to tune\nand monitor different aspects of `VACUUM` operations.\n\nOverview\n--------\n\nThis document covers the following:\n\n- Freezing transaction IDs.\n- Monitoring transaction IDs.\n- Reclaiming storage space.\n- Configuring automated Cloud Monitoring alerts.\n\nTo read the full white paper, click the button:\n\n[Download the PDF](/static/solutions/optimizing-monitoring-troubleshooting-vacuum-operations-postgresql.pdf)"]]
