Reading Table Bloat Before It Reads You
Blog post from Tiger Data
Append-only PostgreSQL tables can accumulate substantial dead space despite never being updated, primarily through aborted insert batches, while insert-triggered autovacuum may run frequently to freeze tuples and maintain visibility metadata. The post explains how to use statistics from pg_stat_user_tables to rank tables by estimated dead tuples, dead-space ratio, insert activity, size, and autovacuum recency, distinguishing between healthy vacuum activity, workloads where vacuum is falling behind, and cleanup blocked by long-running transactions or replication slots. It also notes that index bloat requires separate density measurements with pgstatindex, with nonsequential B-tree indexes such as those on device identifiers often more vulnerable than time-ordered indexes. Recommended practices include applying fixed per-partition autovacuum thresholds rather than large-table scale factors, increasing per-table vacuum cost limits where appropriate, ensuring future partitions inherit settings, and alerting when dead-space ratios rise or autovacuum becomes unexpectedly stale. Plain VACUUM reclaims space for reuse rather than shrinking files, and persistent growth after tuning may indicate that storage architecture rather than vacuum configuration is the limiting factor.
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