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Re-work standby side metrics to be based around the `pg_stat_wal_rece…
…iver` view
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Andrew Morton
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Apr 28, 2022
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| Original file line number | Diff line number | Diff line change |
|---|---|---|
| @@ -0,0 +1,84 @@ | ||
| package collector | ||
|
|
||
| import ( | ||
| "context" | ||
|
|
||
| pgx "github.com/jackc/pgx/v4" | ||
| "github.com/prometheus/client_golang/prometheus" | ||
| ) | ||
|
|
||
| /* When pg_basebackup is running in stream mode, it opens a second connection | ||
| to the server and starts streaming the transaction log in parallel while | ||
| running the backup. In both connections (state=backup and state=streaming) the | ||
| pg_log_location_diff is null and it requires to be excluded */ | ||
| const ( | ||
| // Scrape query | ||
| statWalReceiver = ` | ||
| WITH pg_wal_receiver AS ( | ||
| SELECT status | ||
| , ( | ||
| CASE WHEN pg_last_wal_receive_lsn() = pg_last_wal_replay_lsn() | ||
| THEN 0 | ||
| ELSE EXTRACT (EPOCH FROM now() - pg_last_xact_replay_timestamp()) | ||
| END | ||
| ) as postgres_wal_receiver_replay_lag | ||
| FROM pg_stat_wal_receiver | ||
| ) | ||
| SELECT * FROM pg_wal_receiver WHERE postgres_wal_receiver_replay_lag IS NOT NULL /*postgres_exporter*/` | ||
| ) | ||
|
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| type statWalReceiverScraper struct { | ||
| walReceiverReplayLag *prometheus.Desc | ||
| } | ||
|
|
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| // NewStatWalReceiverScraper returns a new Scraper exposing postgres pg_stat_replication | ||
| func NewWalReceiverScraper() Scraper { | ||
| return &statWalReceiverScraper{ | ||
| walReceiverReplayLag: prometheus.NewDesc( | ||
| "postgres_wal_receiver_replay_lag_seconds", | ||
| "delay in standby wal replay seconds EXTRACT (EPOCH FROM now() - pg_last_xact_replay_timestamp()", | ||
| []string{"status"}, | ||
| nil, | ||
| ), | ||
| } | ||
| } | ||
|
|
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| func (c *statWalReceiverScraper) Name() string { | ||
| return "StatWalReceiverScraperr" | ||
| } | ||
|
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| func (c *statWalReceiverScraper) Scrape(ctx context.Context, conn *pgx.Conn, version Version, ch chan<- prometheus.Metric) error { | ||
| var rows pgx.Rows | ||
| var err error | ||
|
|
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| rows, err = conn.Query(ctx, statWalReceiver) | ||
|
|
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| if err != nil { | ||
| return err | ||
| } | ||
| defer rows.Close() | ||
|
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| var status string | ||
| var pgWalReceiverReplayLag float64 | ||
|
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| for rows.Next() { | ||
|
|
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| if err := rows.Scan(&status, | ||
| &pgWalReceiverReplayLag); err != nil { | ||
|
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| return err | ||
| } | ||
| // postgres_wal_receiver_replay_lag_seconds | ||
| ch <- prometheus.MustNewConstMetric(c.walReceiverReplayLag, | ||
| prometheus.GaugeValue, | ||
| pgWalReceiverReplayLag, | ||
| status) | ||
| } | ||
|
|
||
| err = rows.Err() | ||
| if err != nil { | ||
| return err | ||
| } | ||
|
|
||
| return nil | ||
| } |