[receiver/postgresql] Add optional postgresql.database.locks metric (#…

…26318)

**Description:** Added new metric -- postgresql.database_locks -- the
number of database locks .

**Link to tracking Issue:** #26317

**Testing:** <Describe what testing was performed and which tests were
added.>

**Documentation:** <Describe the documentation added.>

---------

Co-authored-by: Antoine Toulme <antoine@toulme.name>

.chloggen/added-datbase-locks-metric.yaml

@@ -0,0 +1,27 @@
+# Use this changelog template to create an entry for release notes.
+
+# One of 'breaking', 'deprecation', 'new_component', 'enhancement', 'bug_fix'
+change_type: enhancement
+
+# The name of the component, or a single word describing the area of concern, (e.g. filelogreceiver)
+component: postgresqlreceiver
+
+# A brief description of the change.  Surround your text with quotes ("") if it needs to start with a backtick (`).
+note: Added `postgresql.database.locks` metric.
+
+# Mandatory: One or more tracking issues related to the change. You can use the PR number here if no issue exists.
+issues: [26317]
+
+# (Optional) One or more lines of additional information to render under the primary note.
+# These lines will be padded with 2 spaces and then inserted directly into the document.
+# Use pipe (|) for multiline entries.
+subtext:
+
+# If your change doesn't affect end users or the exported elements of any package,
+# you should instead start your pull request title with [chore] or use the "Skip Changelog" label.
+# Optional: The change log or logs in which this entry should be included.
+# e.g. '[user]' or '[user, api]'
+# Include 'user' if the change is relevant to end users.
+# Include 'api' if there is a change to a library API.
+# Default: '[user]'
+change_logs: [user]

receiver/postgresqlreceiver/client.go

@@ -36,6 +36,7 @@ var errNoLastArchive = errors.New("no last archive found, not able to calculate
 type client interface {
 	Close() error
 	getDatabaseStats(ctx context.Context, databases []string) (map[databaseName]databaseStats, error)
+	getDatabaseLocks(ctx context.Context) ([]databaseLocks, error)
 	getBGWriterStats(ctx context.Context) (*bgStat, error)
 	getBackends(ctx context.Context, databases []string) (map[databaseName]int64, error)
 	getDatabaseSize(ctx context.Context, databases []string) (map[databaseName]int64, error)
@@ -163,6 +164,44 @@ func (c *postgreSQLClient) getDatabaseStats(ctx context.Context, databases []str
 	return dbStats, errs
 }
 
+type databaseLocks struct {
+	relation string
+	mode     string
+	lockType string
+	locks    int64
+}
+
+func (c *postgreSQLClient) getDatabaseLocks(ctx context.Context) ([]databaseLocks, error) {
+	query := `SELECT relname AS relation, mode, locktype,COUNT(pid)
+	AS locks FROM pg_locks
+	JOIN pg_class ON pg_locks.relation = pg_class.oid
+	GROUP BY relname, mode, locktype;`
+
+	rows, err := c.client.QueryContext(ctx, query)
+	if err != nil {
+		return nil, fmt.Errorf("unable to query pg_locks and pg_locks.relation: %w", err)
+	}
+	defer rows.Close()
+	var dl []databaseLocks
+	var errs []error
+	for rows.Next() {
+		var relation, mode, lockType string
+		var locks int64
+		err = rows.Scan(&relation, &mode, &lockType, &locks)
+		if err != nil {
+			errs = append(errs, err)
+			continue
+		}
+		dl = append(dl, databaseLocks{
+			relation: relation,
+			mode:     mode,
+			lockType: lockType,
+			locks:    locks,
+		})
+	}
+	return dl, multierr.Combine(errs...)
+}
+
 // getBackends returns a map of database names to the number of active connections
 func (c *postgreSQLClient) getBackends(ctx context.Context, databases []string) (map[databaseName]int64, error) {
 	query := filterQueryByDatabases("SELECT datname, count(*) as count from pg_stat_activity", databases, true)

receiver/postgresqlreceiver/documentation.md

@@ -253,6 +253,22 @@ metrics:
     enabled: true
 ```
 
+### postgresql.database.locks
+
+The number of database locks.
+
+| Unit | Metric Type | Value Type |
+| ---- | ----------- | ---------- |
+| {lock} | Gauge | Int |
+
+#### Attributes
+
+| Name | Description | Values |
+| ---- | ----------- | ------ |
+| relation | OID of the relation targeted by the lock, or null if the target is not a relation or part of a relation. | Any Str |
+| mode | Name of the lock mode held or desired by the process. | Any Str |
+| lock_type | Type of the lockable object. | Any Str |
+
 ### postgresql.deadlocks
 
 The number of deadlocks.

receiver/postgresqlreceiver/integration_test.go

@@ -61,6 +61,7 @@ func integrationTest(name string, databases []string) func(*testing.T) {
 				rCfg.Metrics.PostgresqlDeadlocks.Enabled = true
 				rCfg.Metrics.PostgresqlTempFiles.Enabled = true
 				rCfg.Metrics.PostgresqlSequentialScans.Enabled = true
+				rCfg.Metrics.PostgresqlDatabaseLocks.Enabled = true
 			}),
 		scraperinttest.WithExpectedFile(expectedFile),
 		scraperinttest.WithCompareOptions(

receiver/postgresqlreceiver/internal/metadata/testdata/config.yaml

@@ -21,6 +21,8 @@ all_set:
       enabled: true
     postgresql.database.count:
       enabled: true
+    postgresql.database.locks:
+      enabled: true
     postgresql.db_size:
       enabled: true
     postgresql.deadlocks:
@@ -80,6 +82,8 @@ none_set:
       enabled: false
     postgresql.database.count:
       enabled: false
+    postgresql.database.locks:
+      enabled: false
     postgresql.db_size:
       enabled: false
     postgresql.deadlocks:

receiver/postgresqlreceiver/metadata.yaml

@@ -46,6 +46,12 @@ attributes:
       - sync
       - write
     name_override: type
+  lock_type:
+    description: Type of the lockable object.
+    type: string
+  mode:
+    description: Name of the lock mode held or desired by the process.
+    type: string
   source:
     description: The block read source type.
     type: string
@@ -62,6 +68,9 @@ attributes:
     description: The database operation.
     type: string
     enum: [ins, upd, del, hot_upd]
+  relation:
+    description: OID of the relation targeted by the lock, or null if the target is not a relation or part of a relation.
+    type: string
   replication_client:
     description: The IP address of the client connected to this backend. If this field is "unix", it indicates either that the client is connected via a Unix socket.
     type: string
@@ -147,6 +156,13 @@ metrics:
       monotonic: false
       value_type: int
     unit: "{databases}"
+  postgresql.database.locks:
+    enabled: false
+    description: The number of database locks.
+    unit: "{lock}"
+    gauge:
+      value_type: int
+    attributes: [relation, mode, lock_type]
   postgresql.db_size:
     enabled: true
     description: The database disk usage.

receiver/postgresqlreceiver/scraper.go

@@ -132,6 +132,7 @@ func (p *postgreSQLScraper) scrape(ctx context.Context) (pmetric.Metrics, error)
 	p.collectWalAge(ctx, now, listClient, &errs)
 	p.collectReplicationStats(ctx, now, listClient, &errs)
 	p.collectMaxConnections(ctx, now, listClient, &errs)
+	p.collectDatabaseLocks(ctx, now, listClient, &errs)
 
 	return p.mb.Emit(), errs.combine()
 }
@@ -266,6 +267,23 @@ func (p *postgreSQLScraper) collectBGWriterStats(
 	p.mb.RecordPostgresqlBgwriterMaxwrittenDataPoint(now, bgStats.maxWritten)
 }
 
+func (p *postgreSQLScraper) collectDatabaseLocks(
+	ctx context.Context,
+	now pcommon.Timestamp,
+	client client,
+	errs *errsMux,
+) {
+	dbLocks, err := client.getDatabaseLocks(ctx)
+	if err != nil {
+		p.logger.Error("Errors encountered while fetching database locks", zap.Error(err))
+		errs.addPartial(err)
+		return
+	}
+	for _, dbLock := range dbLocks {
+		p.mb.RecordPostgresqlDatabaseLocksDataPoint(now, dbLock.locks, dbLock.relation, dbLock.mode, dbLock.lockType)
+	}
+}
+
 func (p *postgreSQLScraper) collectMaxConnections(
 	ctx context.Context,
 	now pcommon.Timestamp,