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fix: handle NULL pg_stat_wal.stats_reset #1

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fix: handle NULL pg_stat_wal.stats_reset #1

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48 changes: 28 additions & 20 deletions pkg/management/postgres/probes.go
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Original file line number Diff line number Diff line change
Expand Up @@ -26,6 +26,7 @@ import (
"path/filepath"
"strings"

"github.com/blang/semver"
"github.com/cloudnative-pg/machinery/pkg/fileutils"
"github.com/cloudnative-pg/machinery/pkg/log"
corev1 "k8s.io/api/core/v1"
Expand Down Expand Up @@ -594,7 +595,7 @@ type PgStatWal struct {
WalSync int64
WalWriteTime float64
WalSyncTime float64
StatsReset string
StatsReset sql.NullString
}

// TryGetPgStatWAL retrieves pg_stat_wal on pg version 14 and further
Expand All @@ -609,12 +610,21 @@ func (instance *Instance) TryGetPgStatWAL() (*PgStatWal, error) {
return nil, err
}

// Since PostgreSQL 18, `wal_write`, `wal_sync`, `wal_write_time` and
// `wal_sync_time` have been removed.
// See https://github.com/postgres/postgres/commit/2421e9a51d20bb83154e54a16ce628f9249fa907
return getPgStatWAL(superUserDB, version)
}

// getPgStatWAL scans pg_stat_wal from the given DB. The query shape depends on
// the major version because PostgreSQL 18 removed `wal_write`, `wal_sync`,
// `wal_write_time` and `wal_sync_time` (see
// https://github.com/postgres/postgres/commit/2421e9a51d20bb83154e54a16ce628f9249fa907).
// `stats_reset` is scanned as `sql.NullString` because it is legitimately NULL
// on instances that have never had WAL stats initialized — in particular
// replicas, and primaries that were promoted from a replica bootstrapped via
// `pg_basebackup`.
func getPgStatWAL(db *sql.DB, version semver.Version) (*PgStatWal, error) {
var pgWalStat PgStatWal
if version.Major < 18 {
row := superUserDB.QueryRow(
row := db.QueryRow(
`SELECT
wal_records,
wal_fpi,
Expand All @@ -639,28 +649,26 @@ func (instance *Instance) TryGetPgStatWAL() (*PgStatWal, error) {
); err != nil {
return nil, err
}
return &pgWalStat, nil
}

if version.Major >= 18 {
row := superUserDB.QueryRow(
`SELECT
wal_records,
row := db.QueryRow(
`SELECT
wal_records,
wal_fpi,
wal_bytes,
wal_buffers_full,
stats_reset
FROM pg_catalog.pg_stat_wal`)
if err := row.Scan(
&pgWalStat.WalRecords,
&pgWalStat.WalFpi,
&pgWalStat.WalBytes,
&pgWalStat.WALBuffersFull,
&pgWalStat.StatsReset,
); err != nil {
return nil, err
}
FROM pg_catalog.pg_stat_wal`)
if err := row.Scan(
&pgWalStat.WalRecords,
&pgWalStat.WalFpi,
&pgWalStat.WalBytes,
&pgWalStat.WALBuffersFull,
&pgWalStat.StatsReset,
); err != nil {
return nil, err
}

return &pgWalStat, nil
}

Expand Down
74 changes: 74 additions & 0 deletions pkg/management/postgres/probes_test.go
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Original file line number Diff line number Diff line change
Expand Up @@ -267,3 +267,77 @@ var _ = Describe("probes", func() {
})
})
})

var _ = Describe("getPgStatWAL", func() {
pgStatWalColumns := []string{
"wal_records",
"wal_fpi",
"wal_bytes",
"wal_buffers_full",
"wal_write",
"wal_sync",
"wal_write_time",
"wal_sync_time",
"stats_reset",
}

pg18Columns := []string{
"wal_records",
"wal_fpi",
"wal_bytes",
"wal_buffers_full",
"stats_reset",
}

It("returns the parsed stats when stats_reset is populated (PG<18)", func() {
db, mock, err := sqlmock.New()
Expect(err).ToNot(HaveOccurred())
defer func() { _ = db.Close() }()

mock.ExpectQuery(`FROM pg_catalog.pg_stat_wal`).
WillReturnRows(sqlmock.NewRows(pgStatWalColumns).
AddRow(int64(10), int64(20), int64(30), int64(40),
int64(50), int64(60), float64(70), float64(80),
"2026-05-04 12:00:00+00"))

stat, err := getPgStatWAL(db, semver.Version{Major: 17})
Expect(err).ToNot(HaveOccurred())
Expect(stat).NotTo(BeNil())
Expect(stat.WalRecords).To(Equal(int64(10)))
Expect(stat.StatsReset.Valid).To(BeTrue())
Expect(stat.StatsReset.String).To(Equal("2026-05-04 12:00:00+00"))
})

It("does not error when stats_reset is NULL (PG<18, replica or post-promotion primary)", func() {
db, mock, err := sqlmock.New()
Expect(err).ToNot(HaveOccurred())
defer func() { _ = db.Close() }()

mock.ExpectQuery(`FROM pg_catalog.pg_stat_wal`).
WillReturnRows(sqlmock.NewRows(pgStatWalColumns).
AddRow(int64(0), int64(0), int64(0), int64(0),
int64(0), int64(0), float64(0), float64(0),
nil))

stat, err := getPgStatWAL(db, semver.Version{Major: 17})
Expect(err).ToNot(HaveOccurred())
Expect(stat).NotTo(BeNil())
Expect(stat.StatsReset.Valid).To(BeFalse())
Expect(stat.StatsReset.String).To(Equal(""))
})

It("does not error when stats_reset is NULL (PG>=18)", func() {
db, mock, err := sqlmock.New()
Expect(err).ToNot(HaveOccurred())
defer func() { _ = db.Close() }()

mock.ExpectQuery(`FROM pg_catalog.pg_stat_wal`).
WillReturnRows(sqlmock.NewRows(pg18Columns).
AddRow(int64(0), int64(0), int64(0), int64(0), nil))

stat, err := getPgStatWAL(db, semver.Version{Major: 18})
Expect(err).ToNot(HaveOccurred())
Expect(stat).NotTo(BeNil())
Expect(stat.StatsReset.Valid).To(BeFalse())
})
})
16 changes: 8 additions & 8 deletions pkg/management/postgres/webserver/metricserver/wal.go
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Original file line number Diff line number Diff line change
Expand Up @@ -50,15 +50,15 @@ func collectPGStatWAL(e *Exporter) error {
return err
}
walMetrics := e.Metrics.PgStatWalMetrics
walMetrics.WalRecords.WithLabelValues(walStat.StatsReset).Set(float64(walStat.WalRecords))
walMetrics.WalFpi.WithLabelValues(walStat.StatsReset).Set(float64(walStat.WalFpi))
walMetrics.WalBytes.WithLabelValues(walStat.StatsReset).Set(float64(walStat.WalBytes))
walMetrics.WALBuffersFull.WithLabelValues(walStat.StatsReset).Set(float64(walStat.WALBuffersFull))
walMetrics.WalRecords.WithLabelValues(walStat.StatsReset.String).Set(float64(walStat.WalRecords))
walMetrics.WalFpi.WithLabelValues(walStat.StatsReset.String).Set(float64(walStat.WalFpi))
walMetrics.WalBytes.WithLabelValues(walStat.StatsReset.String).Set(float64(walStat.WalBytes))
walMetrics.WALBuffersFull.WithLabelValues(walStat.StatsReset.String).Set(float64(walStat.WALBuffersFull))
if version, _ := e.instance.GetPgVersion(); version.Major < 18 {
walMetrics.WalWrite.WithLabelValues(walStat.StatsReset).Set(float64(walStat.WalWrite))
walMetrics.WalSync.WithLabelValues(walStat.StatsReset).Set(float64(walStat.WalSync))
walMetrics.WalWriteTime.WithLabelValues(walStat.StatsReset).Set(walStat.WalWriteTime)
walMetrics.WalSyncTime.WithLabelValues(walStat.StatsReset).Set(walStat.WalSyncTime)
walMetrics.WalWrite.WithLabelValues(walStat.StatsReset.String).Set(float64(walStat.WalWrite))
walMetrics.WalSync.WithLabelValues(walStat.StatsReset.String).Set(float64(walStat.WalSync))
walMetrics.WalWriteTime.WithLabelValues(walStat.StatsReset.String).Set(walStat.WalWriteTime)
walMetrics.WalSyncTime.WithLabelValues(walStat.StatsReset.String).Set(walStat.WalSyncTime)
}

return nil
Expand Down