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add pg_stat_statements plans #1315

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add pg_stat_statements plans #1315

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48 changes: 44 additions & 4 deletions collector/pg_stat_statements.go
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Original file line number Diff line number Diff line change
Expand Up @@ -110,6 +110,18 @@ func NewPGStatStatementsCollector(config collectorConfig) (Collector, error) {
}

var (
statStatementsPlansTotal = prometheus.NewDesc(
prometheus.BuildFQName(namespace, statStatementsSubsystem, "plans_total"),
"Number of times planned",
[]string{"user", "datname", "queryid"},
prometheus.Labels{},
)
statStatementsPlansSecondsTotal = prometheus.NewDesc(
prometheus.BuildFQName(namespace, statStatementsSubsystem, "plans_seconds_total"),
"Total time spent in planning the statement, in seconds",
[]string{"user", "datname", "queryid"},

@ArthurSens ArthurSens Jun 9, 2026

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queryID looks like a label with unbounded cardinality. Could we drop it?

@jfcoz jfcoz Jun 9, 2026

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I need it, for example to get the ratio of calls by plan and find queries which are badly used (for example prepare + bind inside a loop)

@ArthurSens ArthurSens Jun 9, 2026

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This doesn't work well with Prometheus though 😅.

Maybe that could become an exemplar label in the histogram?

@jfcoz jfcoz Jun 9, 2026

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I don’t understand the problem. It’s already the same in all the other metrics from pg_stat_statements.

@ArthurSens ArthurSens Jun 9, 2026

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Apologies, I probably should have said this from the beginning. I'm not a maintainer for this repository! If the maintainers are ok with it, that's what counts

@ArthurSens ArthurSens Jun 9, 2026 •
edited
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What I meant by "this doesn't work well with Prometheus" is that a single query will have a single ID and generate a single timeseries; another query will get a different ID and therefore become a brand-new timeseries.

All those unique IDs will become an entry in Prometheus's Posting index (good blog in case you'd like to read more). A gigantic posting index will make PromQL queries slower and increase resource usage

prometheus.Labels{},
)
statStatementsCallsTotal = prometheus.NewDesc(
prometheus.BuildFQName(namespace, statStatementsSubsystem, "calls_total"),
"Number of times executed",
Expand Down Expand Up @@ -159,6 +171,8 @@ const (
pg_database.datname,
pg_stat_statements.queryid,
%s
0 as plans_total,
0 as plans_seconds_total,
Comment on lines +174 to +175

@ArthurSens ArthurSens Sep 10, 2026

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Not emitting the metric at all sounds better than a 0, people might misinterpret this as the table actually returning 0.

pg_stat_statements.calls as calls_total,
pg_stat_statements.total_time / 1000.0 as seconds_total,
pg_stat_statements.rows as rows_total,
Expand All @@ -182,6 +196,8 @@ const (
pg_database.datname,
pg_stat_statements.queryid,
%s
pg_stat_statements.plans as plans_total,
pg_stat_statements.total_plan_time / 1000.0 as plans_seconds_total,
pg_stat_statements.calls as calls_total,
pg_stat_statements.total_exec_time / 1000.0 as seconds_total,
pg_stat_statements.rows as rows_total,
Expand All @@ -205,6 +221,8 @@ const (
pg_database.datname,
pg_stat_statements.queryid,
%s
pg_stat_statements.plans as plans_total,
pg_stat_statements.total_plan_time / 1000.0 as plans_seconds_total,
pg_stat_statements.calls as calls_total,
pg_stat_statements.total_exec_time / 1000.0 as seconds_total,
pg_stat_statements.rows as rows_total,
Expand Down Expand Up @@ -259,13 +277,13 @@ func (c PGStatStatementsCollector) Update(ctx context.Context, instance *instanc
defer rows.Close()
for rows.Next() {
var user, datname, queryid, statement sql.NullString
var callsTotal, rowsTotal sql.NullInt64
var secondsTotal, blockReadSecondsTotal, blockWriteSecondsTotal sql.NullFloat64
var plansTotal, callsTotal, rowsTotal sql.NullInt64
var plansSecondsTotal, secondsTotal, blockReadSecondsTotal, blockWriteSecondsTotal sql.NullFloat64
var columns []any
if c.includeQueryStatement {
columns = []any{&user, &datname, &queryid, &statement, &callsTotal, &secondsTotal, &rowsTotal, &blockReadSecondsTotal, &blockWriteSecondsTotal}
columns = []any{&user, &datname, &queryid, &statement, &plansTotal, &plansSecondsTotal, &callsTotal, &secondsTotal, &rowsTotal, &blockReadSecondsTotal, &blockWriteSecondsTotal}
} else {
columns = []any{&user, &datname, &queryid, &callsTotal, &secondsTotal, &rowsTotal, &blockReadSecondsTotal, &blockWriteSecondsTotal}
columns = []any{&user, &datname, &queryid, &plansTotal, &plansSecondsTotal, &callsTotal, &secondsTotal, &rowsTotal, &blockReadSecondsTotal, &blockWriteSecondsTotal}
}
if err := rows.Scan(columns...); err != nil {
return err
Expand All @@ -292,6 +310,28 @@ func (c PGStatStatementsCollector) Update(ctx context.Context, instance *instanc
}
seen[key] = struct{}{}

plansTotalMetric := 0.0
if plansTotal.Valid {
plansTotalMetric = float64(plansTotal.Int64)
}
ch <- prometheus.MustNewConstMetric(
statStatementsPlansTotal,
prometheus.CounterValue,
plansTotalMetric,
userLabel, datnameLabel, queryidLabel,
)

plansSecondsTotalMetric := 0.0
if plansSecondsTotal.Valid {
plansSecondsTotalMetric = plansSecondsTotal.Float64
}
ch <- prometheus.MustNewConstMetric(
statStatementsPlansSecondsTotal,
prometheus.CounterValue,
plansSecondsTotalMetric,
userLabel, datnameLabel, queryidLabel,
)

callsTotalMetric := 0.0
if callsTotal.Valid {
callsTotalMetric = float64(callsTotal.Int64)
Expand Down
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