PostgreSQLFlexDatabaseXacts — Remaining transactions

Per-database transaction-ID (XID) and multixact-ID (MXID) consumption. The key signal for transaction-ID wraparound prevention — Postgres will force the cluster into read-only mode if XIDs are exhausted.

Kusto query

let server = "my-pg-prd-1";
AzureDiagnostics
| where Category == "PostgreSQLFlexDatabaseXacts" and LogicalServerName_s == server
| project DatabaseName_s, Datdba_d, DatConnLimit_d,
          DatFrozenxid_d, DatMinmxid_d, Age_DatFrozenxid_d, Age_DatMinmxid_d,
          Autovacuum_freeze_max_age_d, Autovacuum_multixact_freeze_max_age_d,
          Vacuum_freeze_min_age_d, Vacuum_multixact_freeze_min_age_d,
          Remaining_xids_till_emergency_autovacuum_d, Remaining_xids_till_wraparound_d,
          Remaining_mxids_till_emergency_autovacuum_d, Remaining_mxids_till_wraparound_d,
          Total_remaining_xids_d, Total_remaining_mxids_d

Fields

Database identity

• DatabaseName_s (string) — database name.
• Datdba_d (number) — OID of the database owner.
• DatConnLimit_d (number) — per-database connection limit (-1 = no limit).

Frozen-ID watermarks

• DatFrozenxid_d (number) — oldest unfrozen XID in the database.
• DatMinmxid_d (number) — oldest multixact ID in the database.
• Age_DatFrozenxid_d (number) — age (XIDs elapsed) since datfrozenxid.
• Age_DatMinmxid_d (number) — age since datminmxid.

Vacuum thresholds (effective settings)

• Autovacuum_freeze_max_age_d (number) — XID age that forces an anti-wraparound autovacuum.
• Autovacuum_multixact_freeze_max_age_d (number) — MXID age that forces it.
• Vacuum_freeze_min_age_d (number) — min XID age before tuples get frozen.
• Vacuum_multixact_freeze_min_age_d (number) — min MXID age before freezing.

Remaining headroom (alerting signals)

• Remaining_xids_till_emergency_autovacuum_d (number) — XIDs left before emergency autovacuum kicks in.
• Remaining_xids_till_wraparound_d (number) — XIDs left before wraparound / shutdown.
• Remaining_mxids_till_emergency_autovacuum_d (number) — MXIDs left before emergency autovacuum.
• Remaining_mxids_till_wraparound_d (number) — MXIDs left before MXID wraparound.
• Total_remaining_xids_d / Total_remaining_mxids_d (number) — total XID/MXID budget remaining.

Use cases — troubleshooting

• Transaction-ID wraparound prevention — alert when Remaining_xids_till_wraparound_d / Remaining_mxids_till_wraparound_d drop dangerously low (risk of forced read-only shutdown).
• Emergency-autovacuum prediction — watch Remaining_xids_till_emergency_autovacuum_d to anticipate aggressive anti-wraparound vacuums (and the I/O they cause).
• Find the worst database — rank databases by Age_DatFrozenxid_d / Age_DatMinmxid_d to see which one drives the cluster's XID age.
• MultiXact exhaustion — track Age_DatMinmxid_d / remaining MXIDs for heavy SELECT ... FOR SHARE/FK-locking workloads.
• Vacuum-policy validation — confirm Autovacuum_freeze_max_age_d and related thresholds are set sensibly for the consumption rate.