stats-split.patch

diff --git a/src/backend/postmaster/pgstat.c b/src/backend/postmaster/pgstat.c
index be3adf1..226311c 100644
--- a/src/backend/postmaster/pgstat.c
+++ b/src/backend/postmaster/pgstat.c
@@ -253,7 +253,9 @@ static PgStat_StatDBEntry *pgstat_get_db_entry(Oid databaseid, bool create);
 static PgStat_StatTabEntry *pgstat_get_tab_entry(PgStat_StatDBEntry *dbentry,
 					 Oid tableoid, bool create);
 static void pgstat_write_statsfile(bool permanent);
-static HTAB *pgstat_read_statsfile(Oid onlydb, bool permanent);
+static void pgstat_write_db_statsfile(PgStat_StatDBEntry * dbentry, bool permanent);
+static HTAB *pgstat_read_statsfile(Oid onlydb, bool permanent, bool onlydbs);
+static void pgstat_read_db_statsfile(Oid databaseid, HTAB *tabhash, HTAB *funchash, bool permanent);
 static void backend_read_statsfile(void);
 static void pgstat_read_current_status(void);
 
@@ -1408,13 +1410,14 @@ pgstat_ping(void)
  * ----------
  */
 static void
-pgstat_send_inquiry(TimestampTz clock_time, TimestampTz cutoff_time)
+pgstat_send_inquiry(TimestampTz clock_time, TimestampTz cutoff_time, Oid databaseid)
 {
 	PgStat_MsgInquiry msg;
 
 	pgstat_setheader(&msg.m_hdr, PGSTAT_MTYPE_INQUIRY);
 	msg.clock_time = clock_time;
 	msg.cutoff_time = cutoff_time;
+	msg.databaseid = databaseid;
 	pgstat_send(&msg, sizeof(msg));
 }
 
@@ -3063,7 +3066,7 @@ PgstatCollectorMain(int argc, char *argv[])
 	 * zero.
 	 */
 	pgStatRunningInCollector = true;
-	pgStatDBHash = pgstat_read_statsfile(InvalidOid, true);
+	pgStatDBHash = pgstat_read_statsfile(InvalidOid, true, false);
 
 	/*
 	 * Loop to process messages until we get SIGQUIT or detect ungraceful
@@ -3435,11 +3438,7 @@ static void
 pgstat_write_statsfile(bool permanent)
 {
 	HASH_SEQ_STATUS hstat;
-	HASH_SEQ_STATUS tstat;
-	HASH_SEQ_STATUS fstat;
 	PgStat_StatDBEntry *dbentry;
-	PgStat_StatTabEntry *tabentry;
-	PgStat_StatFuncEntry *funcentry;
 	FILE	   *fpout;
 	int32		format_id;
 	const char *tmpfile = permanent ? PGSTAT_STAT_PERMANENT_TMPFILE : pgstat_stat_tmpname;
@@ -3493,29 +3492,15 @@ pgstat_write_statsfile(bool permanent)
 		(void) rc;				/* we'll check for error with ferror */
 
 		/*
-		 * Walk through the database's access stats per table.
+		 * Write our the tables and functions into a separate file.
 		 */
-		hash_seq_init(&tstat, dbentry->tables);
-		while ((tabentry = (PgStat_StatTabEntry *) hash_seq_search(&tstat)) != NULL)
-		{
-			fputc('T', fpout);
-			rc = fwrite(tabentry, sizeof(PgStat_StatTabEntry), 1, fpout);
-			(void) rc;			/* we'll check for error with ferror */
-		}
-
-		/*
-		 * Walk through the database's function stats table.
-		 */
-		hash_seq_init(&fstat, dbentry->functions);
-		while ((funcentry = (PgStat_StatFuncEntry *) hash_seq_search(&fstat)) != NULL)
-		{
-			fputc('F', fpout);
-			rc = fwrite(funcentry, sizeof(PgStat_StatFuncEntry), 1, fpout);
-			(void) rc;			/* we'll check for error with ferror */
-		}
+		pgstat_write_db_statsfile(dbentry, permanent);
 
 		/*
 		 * Mark the end of this DB
+		 * 
+		 * FIXME does it really make much sense, when the tables/functions
+		 * are moved to a separate file (using those chars?)
 		 */
 		fputc('d', fpout);
 	}
@@ -3587,6 +3572,111 @@ pgstat_write_statsfile(bool permanent)
 }
 
 
+
+/* ----------
+ * pgstat_write_statsfile() -
+ *
+ *	Tell the news.
+ *	If writing to the permanent file (happens when the collector is
+ *	shutting down only), remove the temporary file so that backends
+ *	starting up under a new postmaster can't read the old data before
+ *	the new collector is ready.
+ * ----------
+ */
+static void
+pgstat_write_db_statsfile(PgStat_StatDBEntry * dbentry, bool permanent)
+{
+	HASH_SEQ_STATUS tstat;
+	HASH_SEQ_STATUS fstat;
+	PgStat_StatTabEntry *tabentry;
+	PgStat_StatFuncEntry *funcentry;
+	FILE	   *fpout;
+	int			rc;
+
+	/* FIXME Disgusting. Handle properly ... */
+	const char *tmpfile_x = permanent ? PGSTAT_STAT_PERMANENT_TMPFILE : pgstat_stat_tmpname;
+	const char *statfile_x = permanent ? PGSTAT_STAT_PERMANENT_FILENAME : pgstat_stat_filename;
+
+	char tmpfile[255];
+	char statfile[255];
+
+	/* FIXME Do some kind of reduction (e.g. mod(oid,255)) not to end with thousands of files,
+	 *one for each database */
+	snprintf(tmpfile, 255, "%s.%d", tmpfile_x, dbentry->databaseid);
+	snprintf(statfile, 255, "%s.%d", statfile_x, dbentry->databaseid);
+
+	/*
+	 * Open the statistics temp file to write out the current values.
+	 */
+	fpout = AllocateFile(tmpfile, PG_BINARY_W);
+	if (fpout == NULL)
+	{
+		ereport(LOG,
+				(errcode_for_file_access(),
+				 errmsg("could not open temporary statistics file \"%s\": %m",
+						tmpfile)));
+		return;
+	}
+
+	/*
+	 * Walk through the database's access stats per table.
+	 */
+	hash_seq_init(&tstat, dbentry->tables);
+	while ((tabentry = (PgStat_StatTabEntry *) hash_seq_search(&tstat)) != NULL)
+	{
+		fputc('T', fpout);
+		rc = fwrite(tabentry, sizeof(PgStat_StatTabEntry), 1, fpout);
+		(void) rc;			/* we'll check for error with ferror */
+	}
+
+	/*
+	 * Walk through the database's function stats table.
+	 */
+	hash_seq_init(&fstat, dbentry->functions);
+	while ((funcentry = (PgStat_StatFuncEntry *) hash_seq_search(&fstat)) != NULL)
+	{
+		fputc('F', fpout);
+		rc = fwrite(funcentry, sizeof(PgStat_StatFuncEntry), 1, fpout);
+		(void) rc;			/* we'll check for error with ferror */
+	}
+
+	/*
+	 * No more output to be done. Close the temp file and replace the old
+	 * pgstat.stat with it.  The ferror() check replaces testing for error
+	 * after each individual fputc or fwrite above.
+	 */
+	fputc('E', fpout);
+
+	if (ferror(fpout))
+	{
+		ereport(LOG,
+				(errcode_for_file_access(),
+			   errmsg("could not write temporary statistics file \"%s\": %m",
+					  tmpfile)));
+		FreeFile(fpout);
+		unlink(tmpfile);
+	}
+	else if (FreeFile(fpout) < 0)
+	{
+		ereport(LOG,
+				(errcode_for_file_access(),
+			   errmsg("could not close temporary statistics file \"%s\": %m",
+					  tmpfile)));
+		unlink(tmpfile);
+	}
+	else if (rename(tmpfile, statfile) < 0)
+	{
+		ereport(LOG,
+				(errcode_for_file_access(),
+				 errmsg("could not rename temporary statistics file \"%s\" to \"%s\": %m",
+						tmpfile, statfile)));
+		unlink(tmpfile);
+	}
+	
+	// if (permanent)
+	//	unlink(pgstat_stat_filename);
+}
+
 /* ----------
  * pgstat_read_statsfile() -
  *
@@ -3595,14 +3685,10 @@ pgstat_write_statsfile(bool permanent)
  * ----------
  */
 static HTAB *
-pgstat_read_statsfile(Oid onlydb, bool permanent)
+pgstat_read_statsfile(Oid onlydb, bool permanent, bool onlydbs)
 {
 	PgStat_StatDBEntry *dbentry;
 	PgStat_StatDBEntry dbbuf;
-	PgStat_StatTabEntry *tabentry;
-	PgStat_StatTabEntry tabbuf;
-	PgStat_StatFuncEntry funcbuf;
-	PgStat_StatFuncEntry *funcentry;
 	HASHCTL		hash_ctl;
 	HTAB	   *dbhash;
 	HTAB	   *tabhash = NULL;
@@ -3758,6 +3844,16 @@ pgstat_read_statsfile(Oid onlydb, bool permanent)
 				 */
 				tabhash = dbentry->tables;
 				funchash = dbentry->functions;
+
+				/*
+				 * Read the data from the file for this database. If there was
+				 * onlydb specified (!= InvalidOid), we would not get here because
+				 * of a break above. So we don't need to recheck.
+				 */
+				if (! onlydbs)
+					pgstat_read_db_statsfile(dbentry->databaseid, tabhash, funchash,
+											permanent);
+
 				break;
 
 				/*
@@ -3768,6 +3864,79 @@ pgstat_read_statsfile(Oid onlydb, bool permanent)
 				funchash = NULL;
 				break;
 
+			case 'E':
+				goto done;
+
+			default:
+				ereport(pgStatRunningInCollector ? LOG : WARNING,
+						(errmsg("corrupted statistics file \"%s\"",
+								statfile)));
+				goto done;
+		}
+	}
+
+done:
+	FreeFile(fpin);
+
+	if (permanent)
+		unlink(PGSTAT_STAT_PERMANENT_FILENAME);
+
+	return dbhash;
+}
+
+
+/* ----------
+ * pgstat_read_db_statsfile() -
+ *
+ *	Reads in an existing statistics collector db file and initializes the
+ *	tables and functions hash tables (for the database identified by Oid).
+ * ----------
+ */
+static void
+pgstat_read_db_statsfile(Oid databaseid, HTAB *tabhash, HTAB *funchash, bool permanent)
+{
+	PgStat_StatTabEntry *tabentry;
+	PgStat_StatTabEntry tabbuf;
+	PgStat_StatFuncEntry funcbuf;
+	PgStat_StatFuncEntry *funcentry;
+	FILE	   *fpin;
+	bool		found;
+
+	/* FIXME Disgusting. Handle properly ... */
+	const char *statfile_x = permanent ? PGSTAT_STAT_PERMANENT_FILENAME : pgstat_stat_filename;
+	char statfile[255];
+
+	/* FIXME Do some kind of reduction (e.g. mod(oid,255)) not to end with thousands of files,
+	 *one for each database */
+	snprintf(statfile, 255, "%s.%d", statfile_x, databaseid);
+
+	/*
+	 * Try to open the status file. If it doesn't exist, the backends simply
+	 * return zero for anything and the collector simply starts from scratch
+	 * with empty counters.
+	 *
+	 * ENOENT is a possibility if the stats collector is not running or has
+	 * not yet written the stats file the first time.  Any other failure
+	 * condition is suspicious.
+	 */
+	if ((fpin = AllocateFile(statfile, PG_BINARY_R)) == NULL)
+	{
+		if (errno != ENOENT)
+			ereport(pgStatRunningInCollector ? LOG : WARNING,
+					(errcode_for_file_access(),
+					 errmsg("could not open statistics file \"%s\": %m",
+							statfile)));
+		return;
+	}
+
+	/*
+	 * We found an existing collector stats file. Read it and put all the
+	 * hashtable entries into place.
+	 */
+	for (;;)
+	{
+		switch (fgetc(fpin))
+		{
 				/*
 				 * 'T'	A PgStat_StatTabEntry follows.
 				 */
@@ -3853,10 +4022,11 @@ pgstat_read_statsfile(Oid onlydb, bool permanent)
 done:
 	FreeFile(fpin);
 
-	if (permanent)
-		unlink(PGSTAT_STAT_PERMANENT_FILENAME);
+// FIXME unlink permanent filename (with the proper Oid appended
+// 	if (permanent)
+// 		unlink(PGSTAT_STAT_PERMANENT_FILENAME);
 
-	return dbhash;
+	return;
 }
 
 /* ----------
@@ -4006,7 +4176,7 @@ backend_read_statsfile(void)
 				pfree(mytime);
 			}
 
-			pgstat_send_inquiry(cur_ts, min_ts);
+			pgstat_send_inquiry(cur_ts, min_ts, InvalidOid);
 			break;
 		}
 
@@ -4016,7 +4186,7 @@ backend_read_statsfile(void)
 
 		/* Not there or too old, so kick the collector and wait a bit */
 		if ((count % PGSTAT_INQ_LOOP_COUNT) == 0)
-			pgstat_send_inquiry(cur_ts, min_ts);
+			pgstat_send_inquiry(cur_ts, min_ts, InvalidOid);
 
 		pg_usleep(PGSTAT_RETRY_DELAY * 1000L);
 	}
@@ -4026,9 +4196,16 @@ backend_read_statsfile(void)
 
 	/* Autovacuum launcher wants stats about all databases */
 	if (IsAutoVacuumLauncherProcess())
-		pgStatDBHash = pgstat_read_statsfile(InvalidOid, false);
+		/* 
+		 * FIXME Does it really need info including tables/functions? Or is it enough to read
+		 * database-level stats? It seems to me the launcher needs PgStat_StatDBEntry only
+		 * (at least that's how I understand the rebuild_database_list() in autovacuum.c),
+		 * because pgstat_stattabentries are used in do_autovacuum() only, that that's what's
+		 * executed in workers ... So maybe we'd be just fine by reading in the dbentries?
+		 */
+		pgStatDBHash = pgstat_read_statsfile(InvalidOid, false, true);
 	else
-		pgStatDBHash = pgstat_read_statsfile(MyDatabaseId, false);
+		pgStatDBHash = pgstat_read_statsfile(MyDatabaseId, false, false);
 }
 
 
diff --git a/src/include/pgstat.h b/src/include/pgstat.h
index 613c1c2..8971002 100644
--- a/src/include/pgstat.h
+++ b/src/include/pgstat.h
@@ -205,6 +205,7 @@ typedef struct PgStat_MsgInquiry
 	PgStat_MsgHdr m_hdr;
 	TimestampTz clock_time;		/* observed local clock time */
 	TimestampTz cutoff_time;	/* minimum acceptable file timestamp */
+	Oid			databaseid;		/* requested DB (InvalidOid => all DBs) */
 } PgStat_MsgInquiry;