PG: Add metrics for pg_stat_replication's sent/write/flush/replay #21844
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integrations-core/postgres/datadog_checks/postgres/postgres.py
Lines 393 to 394 in d26b527
Guard replication stats query on Aurora without logical WAL
The new QUERY_PG_REPLICATION_STATS_METRICS query now calls pg_current_wal_lsn() for every row, but it is still appended unconditionally for all Postgres ≥10 environments. On Aurora instances where wal_level is not set to logical, calling pg_current_wal_lsn() raises an error (this is why the control checkpoint metrics are skipped under the same condition a few lines above). Without a similar guard here, the check will start failing on default Aurora setups. Consider skipping this query when self.is_aurora and self.wal_level != 'logical' or using a function that is allowed on Aurora.
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pg_stat_replication provides metrics on the last sent/write/flush/replay WAL location by a standby server. sent delay doesn't depend on a feedback message from the standby since it tracks the sent WAL through the connection. This can be used to gauge how fast and how late a standby is when catching up
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Only run checkpoint and check metrics on the primary. This will remove the possible uncertainty of having the Checkpoint record being correctly propagated to the standby before standby's checkpoint is triggered.
Add the timestamp to the application name to reduce the risk of leftover query and connection being present when metrics are collected.
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What does this PR do?
Add sent/write/flush/replay lsn delay metrics from pg_stat_replication.
Motivation
pg_stat_replication provides metrics on the last sent/write/flush/replay WAL location by a standby server.
sent delay doesn't depend on a feedback message from the standby since it tracks the sent WAL through the connection. This can be used to gauge how fast and how late a standby is when catching up
Review checklist (to be filled by reviewers)
qa/skip-qalabel if the PR doesn't need to be tested during QA.backport/<branch-name>label to the PR and it will automatically open a backport PR once this one is merged