Session WAL generation statistic

Author: knizhnik

src/backend/access/transam/xlog.c

@@ -1486,6 +1486,9 @@ CopyXLogRecordToWAL(int write_len, bool isLogSwitch, XLogRecData *rdata,
 	currpos = GetXLogBuffer(CurrPos);
 	freespace = INSERT_FREESPACE(CurrPos);
 
+	/* Accumulate amount of data written to WAL for pg_xact_activity */
+	MyProc->walWritten += write_len;
+
 	/*
 	 * there should be enough space for at least the first field (xl_tot_len)
 	 * on this page.

src/backend/catalog/system_views.sql

@@ -758,6 +758,9 @@ CREATE VIEW pg_stat_activity AS
         LEFT JOIN pg_database AS D ON (S.datid = D.oid)
         LEFT JOIN pg_authid AS U ON (S.usesysid = U.oid);
 
+CREATE VIEW pg_stat_wal_activity AS
+    SELECT a.*,pg_stat_get_wal_activity(a.pid) as wal_written FROM pg_stat_activity a;
+
 CREATE VIEW pg_stat_replication AS
     SELECT
             S.pid,

src/backend/storage/lmgr/proc.c

@@ -390,6 +390,8 @@ InitProcess(void)
 	MyPgXact->xid = InvalidTransactionId;
 	MyPgXact->xmin = InvalidTransactionId;
 	MyProc->pid = MyProcPid;
+	MyProc->walWritten = 0;
+
 	/* backendId, databaseId and roleId will be filled in later */
 	MyProc->backendId = InvalidBackendId;
 	MyProc->databaseId = InvalidOid;

src/backend/utils/adt/pgstatfuncs.c

@@ -546,7 +546,8 @@ pg_stat_get_progress_info(PG_FUNCTION_ARGS)
 Datum
 pg_stat_get_activity(PG_FUNCTION_ARGS)
 {
-#define PG_STAT_GET_ACTIVITY_COLS	29
+
+	#define PG_STAT_GET_ACTIVITY_COLS	29
 	int			num_backends = pgstat_fetch_stat_numbackends();
 	int			curr_backend;
 	int			pid = PG_ARGISNULL(0) ? -1 : PG_GETARG_INT32(0);
@@ -918,6 +919,22 @@ pg_stat_get_activity(PG_FUNCTION_ARGS)
 }
 
 
+Datum
+pg_stat_get_wal_activity(PG_FUNCTION_ARGS)
+{
+	int32	pid = PG_GETARG_INT32(0);
+	PGPROC* proc = BackendPidGetProc(pid);
+	if (proc == NULL)
+	{
+		proc = AuxiliaryPidGetProc(pid);
+	}
+	if (proc == NULL)
+		PG_RETURN_NULL();
+	else
+		PG_RETURN_INT64(proc->walWritten);
+}
+
+
 Datum
 pg_backend_pid(PG_FUNCTION_ARGS)
 {

src/include/catalog/pg_proc.dat

@@ -5152,6 +5152,10 @@
   proargmodes => '{i,o,o,o,o,o,o,o,o,o,o,o,o,o,o,o,o,o,o,o,o,o,o,o,o,o,o,o,o,o}',
   proargnames => '{pid,datid,pid,usesysid,application_name,state,query,wait_event_type,wait_event,xact_start,query_start,backend_start,state_change,client_addr,client_hostname,client_port,backend_xid,backend_xmin,backend_type,ssl,sslversion,sslcipher,sslbits,sslcompression,ssl_client_dn,ssl_client_serial,ssl_issuer_dn,gss_auth,gss_princ,gss_enc}',
   prosrc => 'pg_stat_get_activity' },
+{ oid => '2121', descr => 'statistics: WAL activity',
+  proname => 'pg_stat_get_wal_activity', provolatile => 's', proisstrict => 't',
+  proparallel => 'r', prorettype => 'int8', proargtypes => 'int4',
+  prosrc => 'pg_stat_get_wal_activity' },
 { oid => '3318',
   descr => 'statistics: information about progress of backends running maintenance command',
   proname => 'pg_stat_get_progress_info', prorows => '100', proretset => 't',

src/include/storage/proc.h

@@ -203,6 +203,11 @@ struct PGPROC
 	PGPROC	   *lockGroupLeader;	/* lock group leader, if I'm a member */
 	dlist_head	lockGroupMembers;	/* list of members, if I'm a leader */
 	dlist_node	lockGroupLink;	/* my member link, if I'm a member */
+
+	/*
+	 * Amount of data written to the WAL by this process
+	 */
+	uint64      walWritten;
 };
 
 /* NOTE: "typedef struct PGPROC PGPROC" appears in storage/lock.h. */