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Add stat_activity_oldest_backend_xmin #38

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merged 1 commit into from
Feb 27, 2020
Merged

Add stat_activity_oldest_backend_xmin #38

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22 changes: 21 additions & 1 deletion collector/stat_activity.go
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Original file line number Diff line number Diff line change
Expand Up @@ -50,6 +50,11 @@ SELECT EXTRACT(EPOCH FROM age(clock_timestamp(), coalesce(min(query_start), cloc
SELECT EXTRACT(EPOCH FROM age(clock_timestamp(), coalesce(min(query_start), clock_timestamp())))
FROM pg_stat_activity
WHERE backend_xmin IS NOT NULL /*postgres_exporter*/`

// Oldest snapshot transaction ID
// There should be no need to coalesce to a non-null value, as this query
// itself will hold a snapshot even if no other backends have an xmin.
statActivityScraperOldestSnapshotXidQuery = `SELECT min(backend_xmin::text::float) FROM pg_stat_activity /*postgres_exporter*/`
)

type statActivityScraper struct {
Expand All @@ -58,6 +63,7 @@ type statActivityScraper struct {
xact *prometheus.Desc
active *prometheus.Desc
snapshot *prometheus.Desc
xmin *prometheus.Desc
}

// NewStatActivityScraper returns a new Scraper exposing postgres pg_stat_activity
Expand Down Expand Up @@ -93,6 +99,12 @@ func NewStatActivityScraper() Scraper {
nil,
nil,
),
xmin: prometheus.NewDesc(
"postgres_stat_activity_oldest_backend_xmin",
"The lowest backend_xmin across all backends",
nil,
nil,
),
}
}

Expand All @@ -108,7 +120,7 @@ func (c *statActivityScraper) Scrape(ctx context.Context, conn *pgx.Conn, versio
defer rows.Close()

var datname, state string
var count, oldestTx, oldestActive, oldestSnapshot float64
var count, oldestTx, oldestActive, oldestSnapshot, oldestXmin float64
var oldestBackend time.Time

for rows.Next() {
Expand Down Expand Up @@ -157,5 +169,13 @@ func (c *statActivityScraper) Scrape(ctx context.Context, conn *pgx.Conn, versio
// postgres_stat_activity_oldest_snapshot_seconds
ch <- prometheus.MustNewConstMetric(c.snapshot, prometheus.GaugeValue, oldestSnapshot)

err = conn.QueryRow(ctx, statActivityScraperOldestSnapshotXidQuery).Scan(&oldestXmin)
if err != nil {
return err
}

// postgres_stat_activity_oldest_backend_xmin
ch <- prometheus.MustNewConstMetric(c.xmin, prometheus.GaugeValue, oldestXmin)
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I'm pretty sure now that this should be a counter, not a gauge (as long as my assertion about the query that retrieves this metric always holding a snapshot is correct)

Thoughts welcome though


return nil
}