Add the capability to display summary statistics to pg_xlogdump.

The new --stats/--stats=record options to pg_xlogdump display per
rmgr/per record statistics about the parsed WAL. This is useful to
understand what the WAL primarily consists of, to allow targeted
optimizations on application, configuration, and core code level.

It is likely that we will want to fine tune the statistics further,
but the feature already is quite helpful.

Author: Abhijit Menon-Sen, slightly editorialized by me
Reviewed-By: Andres Freund, Dilip Kumar and Furuya Osamu
Discussion: 20140604104716.GA3989@toroid.org

Author: anarazel

contrib/pg_xlogdump/pg_xlogdump.c

@@ -41,13 +41,31 @@ typedef struct XLogDumpConfig
 	int			stop_after_records;
 	int			already_displayed_records;
 	bool		follow;
+	bool		stats;
+	bool		stats_per_record;
 
 	/* filter options */
 	int			filter_by_rmgr;
 	TransactionId filter_by_xid;
 	bool		filter_by_xid_enabled;
 } XLogDumpConfig;
 
+typedef struct Stats
+{
+	uint64		count;
+	uint64		rec_len;
+	uint64		fpi_len;
+} Stats;
+
+#define MAX_XLINFO_TYPES 16
+
+typedef struct XLogDumpStats
+{
+	uint64		count;
+	Stats		rmgr_stats[RM_NEXT_ID];
+	Stats		record_stats[RM_NEXT_ID][MAX_XLINFO_TYPES];
+} XLogDumpStats;
+
 static void
 fatal_error(const char *fmt,...)
 __attribute__((format(PG_PRINTF_ATTRIBUTE, 1, 2)));
@@ -322,22 +340,49 @@ XLogDumpReadPage(XLogReaderState *state, XLogRecPtr targetPagePtr, int reqLen,
 }
 
 /*
- * Print a record to stdout
+ * Store per-rmgr and per-record statistics for a given record.
  */
 static void
-XLogDumpDisplayRecord(XLogDumpConfig *config, XLogRecPtr ReadRecPtr, XLogRecord *record)
+XLogDumpCountRecord(XLogDumpConfig *config, XLogDumpStats *stats, XLogRecPtr ReadRecPtr, XLogRecord *record)
 {
-	const RmgrDescData *desc = &RmgrDescTable[record->xl_rmid];
+	RmgrId		rmid;
+	uint8		recid;
+
+	stats->count++;
 
-	if (config->filter_by_rmgr != -1 &&
-		config->filter_by_rmgr != record->xl_rmid)
-		return;
+	/* Update per-rmgr statistics */
 
-	if (config->filter_by_xid_enabled &&
-		config->filter_by_xid != record->xl_xid)
-		return;
+	rmid = record->xl_rmid;
 
-	config->already_displayed_records++;
+	stats->rmgr_stats[rmid].count++;
+	stats->rmgr_stats[rmid].rec_len +=
+		record->xl_len + SizeOfXLogRecord;
+	stats->rmgr_stats[rmid].fpi_len +=
+		record->xl_tot_len - (record->xl_len + SizeOfXLogRecord);
+
+	/*
+	 * Update per-record statistics, where the record is identified by a
+	 * combination of the RmgrId and the four bits of the xl_info field
+	 * that are the rmgr's domain (resulting in sixteen possible entries
+	 * per RmgrId).
+	 */
+
+	recid = record->xl_info >> 4;
+
+	stats->record_stats[rmid][recid].count++;
+	stats->record_stats[rmid][recid].rec_len +=
+		record->xl_len + SizeOfXLogRecord;
+	stats->record_stats[rmid][recid].fpi_len +=
+		record->xl_tot_len - (record->xl_len + SizeOfXLogRecord);
+}
+
+/*
+ * Print a record to stdout
+ */
+static void
+XLogDumpDisplayRecord(XLogDumpConfig *config, XLogRecPtr ReadRecPtr, XLogRecord *record)
+{
+	const RmgrDescData *desc = &RmgrDescTable[record->xl_rmid];
 
 	printf("rmgr: %-11s len (rec/tot): %6u/%6u, tx: %10u, lsn: %X/%08X, prev %X/%08X, bkp: %u%u%u%u, desc: %s ",
 		   desc->rm_name,
@@ -381,6 +426,134 @@ XLogDumpDisplayRecord(XLogDumpConfig *config, XLogRecPtr ReadRecPtr, XLogRecord
 	}
 }
 
+/*
+ * Display a single row of record counts and sizes for an rmgr or record.
+ */
+static void
+XLogDumpStatsRow(const char *name,
+				 uint64 n, double n_pct,
+				 uint64 rec_len, double rec_len_pct,
+				 uint64 fpi_len, double fpi_len_pct,
+				 uint64 total_len, double total_len_pct)
+{
+	printf("%-27s "
+		   "%20" INT64_MODIFIER "u (%6.02f) "
+		   "%20" INT64_MODIFIER "u (%6.02f) "
+		   "%20" INT64_MODIFIER "u (%6.02f) "
+		   "%20" INT64_MODIFIER "u (%6.02f)\n",
+		   name, n, n_pct, rec_len, rec_len_pct, fpi_len, fpi_len_pct,
+		   total_len, total_len_pct);
+}
+
+
+/*
+ * Display summary statistics about the records seen so far.
+ */
+static void
+XLogDumpDisplayStats(XLogDumpConfig *config, XLogDumpStats *stats)
+{
+	int			ri, rj;
+	uint64		total_count = 0;
+	uint64		total_rec_len = 0;
+	uint64		total_fpi_len = 0;
+	uint64		total_len = 0;
+
+	/* ---
+	 * Make a first pass to calculate column totals:
+	 * count(*),
+	 * sum(xl_len+SizeOfXLogRecord),
+	 * sum(xl_tot_len-xl_len-SizeOfXLogRecord), and
+	 * sum(xl_tot_len).
+	 * These are used to calculate percentages for each record type.
+	 * ---
+	 */
+
+	for (ri = 0; ri < RM_NEXT_ID; ri++)
+	{
+		total_count += stats->rmgr_stats[ri].count;
+		total_rec_len += stats->rmgr_stats[ri].rec_len;
+		total_fpi_len += stats->rmgr_stats[ri].fpi_len;
+	}
+	total_len = total_rec_len+total_fpi_len;
+
+	/*
+	 * 27 is strlen("Transaction/COMMIT_PREPARED"),
+	 * 20 is strlen(2^64), 8 is strlen("(100.00%)")
+	 */
+
+	printf("%-27s %20s %8s %20s %8s %20s %8s %20s %8s\n"
+		   "%-27s %20s %8s %20s %8s %20s %8s %20s %8s\n",
+		   "Type", "N", "(%)", "Record size", "(%)", "FPI size", "(%)", "Combined size", "(%)",
+		   "----", "-", "---", "-----------", "---", "--------", "---", "-------------", "---");
+
+	for (ri = 0; ri < RM_NEXT_ID; ri++)
+	{
+		uint64		count, rec_len, fpi_len, tot_len;
+		const RmgrDescData *desc = &RmgrDescTable[ri];
+
+		if (!config->stats_per_record)
+		{
+			count = stats->rmgr_stats[ri].count;
+			rec_len = stats->rmgr_stats[ri].rec_len;
+			fpi_len = stats->rmgr_stats[ri].fpi_len;
+			tot_len = rec_len + fpi_len;
+
+			XLogDumpStatsRow(desc->rm_name,
+							 count, 100 * (double) count / total_count,
+							 rec_len, 100 * (double) rec_len / total_rec_len,
+							 fpi_len, 100 * (double) fpi_len / total_fpi_len,
+							 tot_len, 100 * (double) tot_len / total_len);
+		}
+		else
+		{
+			for (rj = 0; rj < MAX_XLINFO_TYPES; rj++)
+			{
+				const char *id;
+
+				count = stats->record_stats[ri][rj].count;
+				rec_len = stats->record_stats[ri][rj].rec_len;
+				fpi_len = stats->record_stats[ri][rj].fpi_len;
+				tot_len = rec_len + fpi_len;
+
+				/* Skip undefined combinations and ones that didn't occur */
+				if (count == 0)
+					continue;
+
+				/* the upper four bits in xl_info are the rmgr's */
+				id = desc->rm_identify(rj << 4);
+				if (id == NULL)
+					id = psprintf("UNKNOWN (%x)", rj << 4);
+
+				XLogDumpStatsRow(psprintf("%s/%s", desc->rm_name, id),
+								 count, 100 * (double) count / total_count,
+								 rec_len, 100 * (double) rec_len / total_rec_len,
+								 fpi_len, 100 * (double) fpi_len / total_fpi_len,
+								 tot_len, 100 * (double) tot_len / total_len);
+			}
+		}
+	}
+
+	printf("%-27s %20s %8s %20s %8s %20s %8s %20s\n",
+		   "", "--------", "", "--------", "", "--------", "", "--------");
+
+	/*
+	 * The percentages in earlier rows were calculated against the
+	 * column total, but the ones that follow are against the row total.
+	 * Note that these are displayed with a % symbol to differentiate
+	 * them from the earlier ones, and are thus up to 9 characters long.
+	 */
+
+	printf("%-27s "
+		   "%20" INT64_MODIFIER "u %-9s"
+		   "%20" INT64_MODIFIER "u %-9s"
+		   "%20" INT64_MODIFIER "u %-9s"
+		   "%20" INT64_MODIFIER "u %-6s\n",
+		   "Total", stats->count, "",
+		   total_rec_len, psprintf("[%.02f%%]", 100 * (double)total_rec_len / total_len),
+		   total_fpi_len, psprintf("[%.02f%%]", 100 * (double)total_fpi_len / total_len),
+		   total_len, "[100%]");
+}
+
 static void
 usage(void)
 {
@@ -402,6 +575,8 @@ usage(void)
 	printf("                         (default: 1 or the value used in STARTSEG)\n");
 	printf("  -V, --version          output version information, then exit\n");
 	printf("  -x, --xid=XID          only show records with TransactionId XID\n");
+	printf("  -z, --stats[=record]   show statistics instead of records\n");
+	printf("                         (optionally, show per-record statistics)\n");
 	printf("  -?, --help             show this help, then exit\n");
 }
 
@@ -413,6 +588,7 @@ main(int argc, char **argv)
 	XLogReaderState *xlogreader_state;
 	XLogDumpPrivate private;
 	XLogDumpConfig config;
+	XLogDumpStats stats;
 	XLogRecord *record;
 	XLogRecPtr	first_record;
 	char	   *errormsg;
@@ -429,6 +605,7 @@ main(int argc, char **argv)
 		{"timeline", required_argument, NULL, 't'},
 		{"xid", required_argument, NULL, 'x'},
 		{"version", no_argument, NULL, 'V'},
+		{"stats", optional_argument, NULL, 'z'},
 		{NULL, 0, NULL, 0}
 	};
 
@@ -439,6 +616,7 @@ main(int argc, char **argv)
 
 	memset(&private, 0, sizeof(XLogDumpPrivate));
 	memset(&config, 0, sizeof(XLogDumpConfig));
+	memset(&stats, 0, sizeof(XLogDumpStats));
 
 	private.timeline = 1;
 	private.startptr = InvalidXLogRecPtr;
@@ -452,14 +630,16 @@ main(int argc, char **argv)
 	config.filter_by_rmgr = -1;
 	config.filter_by_xid = InvalidTransactionId;
 	config.filter_by_xid_enabled = false;
+	config.stats = false;
+	config.stats_per_record = false;
 
 	if (argc <= 1)
 	{
 		fprintf(stderr, "%s: no arguments specified\n", progname);
 		goto bad_argument;
 	}
 
-	while ((option = getopt_long(argc, argv, "be:?fn:p:r:s:t:Vx:",
+	while ((option = getopt_long(argc, argv, "be:?fn:p:r:s:t:Vx:z",
 								 long_options, &optindex)) != -1)
 	{
 		switch (option)
@@ -552,6 +732,21 @@ main(int argc, char **argv)
 				}
 				config.filter_by_xid_enabled = true;
 				break;
+			case 'z':
+				config.stats = true;
+				config.stats_per_record = false;
+				if (optarg)
+				{
+					if (strcmp(optarg, "record") == 0)
+						config.stats_per_record = true;
+					else if (strcmp(optarg, "rmgr") != 0)
+					{
+						fprintf(stderr, "%s: unrecognised argument to --stats: %s\n",
+								progname, optarg);
+						goto bad_argument;
+					}
+				}
+				break;
 			default:
 				goto bad_argument;
 		}
@@ -712,14 +907,32 @@ main(int argc, char **argv)
 
 		/* after reading the first record, continue at next one */
 		first_record = InvalidXLogRecPtr;
-		XLogDumpDisplayRecord(&config, xlogreader_state->ReadRecPtr, record);
+
+		/* apply all specified filters */
+		if (config.filter_by_rmgr != -1 &&
+			config.filter_by_rmgr != record->xl_rmid)
+			continue;
+
+		if (config.filter_by_xid_enabled &&
+			config.filter_by_xid != record->xl_xid)
+			continue;
+
+		/* process the record */
+		if (config.stats == true)
+			XLogDumpCountRecord(&config, &stats, xlogreader_state->ReadRecPtr, record);
+		else
+			XLogDumpDisplayRecord(&config, xlogreader_state->ReadRecPtr, record);
 
 		/* check whether we printed enough */
+		config.already_displayed_records++;
 		if (config.stop_after_records > 0 &&
 			config.already_displayed_records >= config.stop_after_records)
 			break;
 	}
 
+	if (config.stats == true)
+		XLogDumpDisplayStats(&config, &stats);
+
 	if (errormsg)
 		fatal_error("error in WAL record at %X/%X: %s\n",
 					(uint32) (xlogreader_state->ReadRecPtr >> 32),

doc/src/sgml/pg_xlogdump.sgml

@@ -179,6 +179,18 @@ PostgreSQL documentation
       </listitem>
      </varlistentry>
 
+     <varlistentry>
+      <term><option>-z</option></term>
+      <term><option>--stats[=record]</option></term>
+      <listitem>
+       <para>
+        Display summary statistics (number and size of records and
+        full-page images) instead of individual records. Optionally
+        generate statistics per-record instead of per-rmgr.
+       </para>
+      </listitem>
+     </varlistentry>
+
      <varlistentry>
       <term><option>-?</></term>
       <term><option>--help</></term>