[receiver/postgresql] Add bgwriter Metrics (#13328)

Adds background writer metrics for the postgresqlreceiver. Feature is behind the receiver.postgresql.emitMetricsWithResourceAttributes feature gate.
- postgresql.bgwriter.buffers.allocated
- postgresql.bgwriter.buffers.writes
- postgresql.bgwriter.checkpoint.count
- postgresql.bgwriter.duration
- postgresql.bgwriter.maxwritten.count

receiver/postgresqlreceiver/client.go

@@ -41,6 +41,7 @@ type indexIdentifer string
 type client interface {
  Close() error
  getDatabaseStats(ctx context.Context, databases []string) (map[databaseName]databaseStats, 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)
  getDatabaseTableMetrics(ctx context.Context, db string) (map[tableIdentifier]tableStats, error)
@@ -361,6 +362,71 @@ func (c *postgreSQLClient) getIndexStats(ctx context.Context, database string) (
  return stats, multierr.Combine(errs...)
 }
 
+type bgStat struct {
+ checkpointsReq int64
+ checkpointsScheduled int64
+ checkpointWriteTime int64
+ checkpointSyncTime int64
+ bgWrites int64
+ backendWrites int64
+ bufferBackendWrites int64
+ bufferFsyncWrites int64
+ bufferCheckpoints int64
+ buffersAllocated int64
+ maxWritten int64
+}
+
+func (c *postgreSQLClient) getBGWriterStats(ctx context.Context) (*bgStat, error) {
+ query := `SELECT 
+ checkpoints_req AS checkpoint_req,
+ checkpoints_timed AS checkpoint_scheduled,
+ checkpoint_write_time AS checkpoint_duration_write,
+ checkpoint_sync_time AS checkpoint_duration_sync,
+ buffers_clean AS bg_writes,
+ buffers_backend AS backend_writes,
+ buffers_backend_fsync AS buffers_written_fsync,
+ buffers_checkpoint AS buffers_checkpoints,
+ buffers_alloc AS buffers_allocated,
+ maxwritten_clean AS maxwritten_count
+ FROM pg_stat_bgwriter;`
+
+ row := c.client.QueryRowContext(ctx, query)
+ var (
+ checkpointsReq, checkpointsScheduled int64
+ checkpointSyncTime, checkpointWriteTime int64
+ bgWrites, bufferCheckpoints, bufferAllocated int64
+ bufferBackendWrites, bufferFsyncWrites, maxWritten int64
+ )
+ err := row.Scan(
+ &checkpointsReq,
+ &checkpointsScheduled,
+ &checkpointWriteTime,
+ &checkpointSyncTime,
+ &bgWrites,
+ &bufferBackendWrites,
+ &bufferFsyncWrites,
+ &bufferCheckpoints,
+ &bufferAllocated,
+ &maxWritten,
+ )
+ if err != nil {
+ return nil, err
+ }
+ return &bgStat{
+ checkpointsReq: checkpointsReq,
+ checkpointsScheduled: checkpointsScheduled,
+ checkpointWriteTime: checkpointWriteTime,
+ checkpointSyncTime: checkpointSyncTime,
+ bgWrites: bgWrites,
+ backendWrites: bufferBackendWrites,
+ bufferBackendWrites: bufferBackendWrites,
+ bufferFsyncWrites: bufferFsyncWrites,
+ bufferCheckpoints: bufferCheckpoints,
+ buffersAllocated: bufferAllocated,
+ maxWritten: maxWritten,
+ }, nil
+}
+
 func (c *postgreSQLClient) listDatabases(ctx context.Context) ([]string, error) {
  query := `SELECT datname FROM pg_database
  WHERE datistemplate = false;`

receiver/postgresqlreceiver/documentation.md

@@ -9,6 +9,11 @@ These are the metrics available for this scraper.
 | Name | Description | Unit | Type | Attributes |
 | ---- | ----------- | ---- | ---- | ---------- |
 | **postgresql.backends** | The number of backends. | 1 | Sum(Int) | <ul> <li>database</li> </ul> |
+| **postgresql.bgwriter.buffers.allocated** | Number of buffers allocated. | {buffers} | Sum(Int) | <ul> </ul> |
+| **postgresql.bgwriter.buffers.writes** | Number of buffers written. | {buffers} | Sum(Int) | <ul> <li>bg_buffer_source</li> </ul> |
+| **postgresql.bgwriter.checkpoint.count** | The number of checkpoints performed. | {checkpoints} | Sum(Int) | <ul> <li>bg_checkpoint_type</li> </ul> |
+| **postgresql.bgwriter.duration** | Total time spent writing and syncing files to disk by checkpoints. | ms | Sum(Int) | <ul> <li>bg_duration_type</li> </ul> |
+| **postgresql.bgwriter.maxwritten** | Number of times the background writer stopped a cleaning scan because it had written too many buffers. | | Sum(Int) | <ul> </ul> |
 | **postgresql.blocks_read** | The number of blocks read. | 1 | Sum(Int) | <ul> <li>database</li> <li>table</li> <li>source</li> </ul> |
 | **postgresql.commits** | The number of commits. | 1 | Sum(Int) | <ul> <li>database</li> </ul> |
 | **postgresql.database.count** | Number of user databases. | {databases} | Sum(Int) | <ul> </ul> |
@@ -43,6 +48,9 @@ metrics:
 
 | Name | Description | Values |
 | ---- | ----------- | ------ |
+| bg_buffer_source (source) | The source of a buffer write. | backend, backend_fsync, checkpoints, bgwriter |
+| bg_checkpoint_type (type) | The type of checkpoint state. | requested, scheduled |
+| bg_duration_type (type) | The type of time spent during the checkpoint. | sync, write |
 | database | The name of the database. | |
 | operation | The database operation. | ins, upd, del, hot_upd |
 | source | The block read source type. | heap_read, heap_hit, idx_read, idx_hit, toast_read, toast_hit, tidx_read, tidx_hit |