pgstat: split reporting/fetching of bgwriter and checkpointer stats.

These have been unrelated since bgwriter and checkpointer were split into two
processes in 806a2aee379. As there several pending patches (shared memory
stats, extending the set of tracked IO / buffer statistics) that are made a
bit more awkward by the grouping, split them. Done separately to make
reviewing easier.

This does *not* change the contents of pg_stat_bgwriter or move fields out of
bgwriter/checkpointer stats that arguably do not belong in either. However
pgstat_fetch_global() was renamed and split into
pgstat_fetch_stat_checkpointer() and pgstat_fetch_stat_bgwriter().

Author: Andres Freund <andres@anarazel.de>
Discussion: https://postgr.es/m/20210405092914.mmxqe7j56lsjfsej@alap3.anarazel.de

1 files changed, 51 insertions, 12 deletions

diff --git a/src/include/pgstat.h b/src/include/pgstat.h
index 9612c0a6c27..2068a68a5ff 100644
--- a/src/include/pgstat.h
+++ b/src/include/pgstat.h
@@ -72,6 +72,7 @@ typedef enum StatMsgType
 	PGSTAT_MTYPE_ANL_ANCESTORS,
 	PGSTAT_MTYPE_ARCHIVER,
 	PGSTAT_MTYPE_BGWRITER,
+	PGSTAT_MTYPE_CHECKPOINTER,
 	PGSTAT_MTYPE_WAL,
 	PGSTAT_MTYPE_SLRU,
 	PGSTAT_MTYPE_FUNCSTAT,
@@ -470,17 +471,27 @@ typedef struct PgStat_MsgBgWriter
 {
 	PgStat_MsgHdr m_hdr;
 
+	PgStat_Counter m_buf_written_clean;
+	PgStat_Counter m_maxwritten_clean;
+	PgStat_Counter m_buf_alloc;
+} PgStat_MsgBgWriter;
+
+/* ----------
+ * PgStat_MsgCheckpointer  Sent by the checkpointer to update statistics.
+ * ----------
+ */
+typedef struct PgStat_MsgCheckpointer
+{
+	PgStat_MsgHdr m_hdr;
+
 	PgStat_Counter m_timed_checkpoints;
 	PgStat_Counter m_requested_checkpoints;
 	PgStat_Counter m_buf_written_checkpoints;
-	PgStat_Counter m_buf_written_clean;
-	PgStat_Counter m_maxwritten_clean;
 	PgStat_Counter m_buf_written_backend;
 	PgStat_Counter m_buf_fsync_backend;
-	PgStat_Counter m_buf_alloc;
 	PgStat_Counter m_checkpoint_write_time; /* times in milliseconds */
 	PgStat_Counter m_checkpoint_sync_time;
-} PgStat_MsgBgWriter;
+} PgStat_MsgCheckpointer;
 
 /* ----------
  * PgStat_MsgWal			Sent by backends and background processes to update WAL statistics.
@@ -700,6 +711,7 @@ typedef union PgStat_Msg
 	PgStat_MsgAnlAncestors msg_anl_ancestors;
 	PgStat_MsgArchiver msg_archiver;
 	PgStat_MsgBgWriter msg_bgwriter;
+	PgStat_MsgCheckpointer msg_checkpointer;
 	PgStat_MsgWal msg_wal;
 	PgStat_MsgSLRU msg_slru;
 	PgStat_MsgFuncstat msg_funcstat;
@@ -721,7 +733,7 @@ typedef union PgStat_Msg
  * ------------------------------------------------------------
  */
 
-#define PGSTAT_FILE_FORMAT_ID	0x01A5BCA2
+#define PGSTAT_FILE_FORMAT_ID	0x01A5BCA3
 
 /* ----------
  * PgStat_StatDBEntry			The collector's data per database
@@ -842,9 +854,20 @@ typedef struct PgStat_ArchiverStats
 } PgStat_ArchiverStats;
 
 /*
- * Global statistics kept in the stats collector
+ * Background writer statistics kept in the stats collector
  */
-typedef struct PgStat_GlobalStats
+typedef struct PgStat_BgWriterStats
+{
+	PgStat_Counter buf_written_clean;
+	PgStat_Counter maxwritten_clean;
+	PgStat_Counter buf_alloc;
+	TimestampTz stat_reset_timestamp;
+} PgStat_BgWriterStats;
+
+/*
+ * Checkpointer statistics kept in the stats collector
+ */
+typedef struct PgStat_CheckpointerStats
 {
 	TimestampTz stats_timestamp;	/* time of stats file update */
 	PgStat_Counter timed_checkpoints;
@@ -852,12 +875,19 @@ typedef struct PgStat_GlobalStats
 	PgStat_Counter checkpoint_write_time;	/* times in milliseconds */
 	PgStat_Counter checkpoint_sync_time;
 	PgStat_Counter buf_written_checkpoints;
-	PgStat_Counter buf_written_clean;
-	PgStat_Counter maxwritten_clean;
 	PgStat_Counter buf_written_backend;
 	PgStat_Counter buf_fsync_backend;
-	PgStat_Counter buf_alloc;
-	TimestampTz stat_reset_timestamp;
+} PgStat_CheckpointerStats;
+
+/*
+ * Global statistics kept in the stats collector
+ */
+typedef struct PgStat_GlobalStats
+{
+	TimestampTz stats_timestamp;	/* time of stats file update */
+
+	PgStat_CheckpointerStats checkpointer;
+	PgStat_BgWriterStats bgwriter;
 } PgStat_GlobalStats;
 
 /*
@@ -939,7 +969,13 @@ extern char *pgstat_stat_filename;
 /*
  * BgWriter statistics counters are updated directly by bgwriter and bufmgr
  */
-extern PgStat_MsgBgWriter BgWriterStats;
+extern PgStat_MsgBgWriter PendingBgWriterStats;
+
+/*
+ * Checkpointer statistics counters are updated directly by checkpointer and
+ * bufmgr.
+ */
+extern PgStat_MsgCheckpointer PendingCheckpointerStats;
 
 /*
  * WAL statistics counter is updated by backends and background processes
@@ -1091,6 +1127,7 @@ extern void pgstat_twophase_postabort(TransactionId xid, uint16 info,
 
 extern void pgstat_send_archiver(const char *xlog, bool failed);
 extern void pgstat_send_bgwriter(void);
+extern void pgstat_send_checkpointer(void);
 extern void pgstat_send_wal(bool force);
 
 /* ----------
@@ -1102,6 +1139,8 @@ extern PgStat_StatDBEntry *pgstat_fetch_stat_dbentry(Oid dbid);
 extern PgStat_StatTabEntry *pgstat_fetch_stat_tabentry(Oid relid);
 extern PgStat_StatFuncEntry *pgstat_fetch_stat_funcentry(Oid funcid);
 extern PgStat_ArchiverStats *pgstat_fetch_stat_archiver(void);
+extern PgStat_BgWriterStats *pgstat_fetch_stat_bgwriter(void);
+extern PgStat_CheckpointerStats *pgstat_fetch_stat_checkpointer(void);
 extern PgStat_GlobalStats *pgstat_fetch_global(void);
 extern PgStat_WalStats *pgstat_fetch_stat_wal(void);
 extern PgStat_SLRUStats *pgstat_fetch_slru(void);