On 11/25/2014 05:36 AM, Andres Freund wrote:
Hi,
The new WAL format calculates FPI vs plain record data like:
rec_len = XLogRecGetDataLen(record) + SizeOfXLogRecord;
fpi_len = record->decoded_record->xl_tot_len - rec_len;
Due to the amount of data now handled outside the main data portion ,
that doesn't seem correct to me. As an example, a couple thousand
inserts with full_page_writes=off now yields:
Type N (%) Record size
(%) FPI size (%) Combined size (%)
---- - --- -----------
--- -------- --- ------------- ---
Heap/INSERT 30167 ( 99.53) 814509
( 99.50) 965856 ( 99.54) 1780365 ( 99.52)
I think fpi_len now needs to only count the sum of the of the actual
length of block images, and all the rest needs to be rec_len.
Yeah, that's broken.
I propose the attached. Or does anyone want to argue for adding an
XLogRecGetFPILen() accessor macro for the hole_length in xlogreader.h.
It's not something a redo routine would need, nor most XLOG-reading
applications, so I thought it's better to just have pg_xlogdump peek
into the DecodedBkpBlock struct directly.
- Heikki
diff --git a/contrib/pg_xlogdump/pg_xlogdump.c b/contrib/pg_xlogdump/pg_xlogdump.c
index 26556dc..9f05e25 100644
--- a/contrib/pg_xlogdump/pg_xlogdump.c
+++ b/contrib/pg_xlogdump/pg_xlogdump.c
@@ -351,14 +351,29 @@ XLogDumpCountRecord(XLogDumpConfig *config, XLogDumpStats *stats,
uint8 recid;
uint32 rec_len;
uint32 fpi_len;
+ int block_id;
stats->count++;
- /* Update per-rmgr statistics */
-
rmid = XLogRecGetRmid(record);
rec_len = XLogRecGetDataLen(record) + SizeOfXLogRecord;
- fpi_len = record->decoded_record->xl_tot_len - rec_len;
+
+ /*
+ * Calculate the amount of FPI data in the record. Each backup block
+ * takes up BLCKSZ bytes, minus the "hole" length.
+ *
+ * XXX: We peek into xlogreader's private decoded backup blocks for the
+ * hole_length. It doesn't seem worth it to add an accessor macro for
+ * this.
+ */
+ fpi_len = 0;
+ for (block_id = 0; block_id <= record->max_block_id; block_id++)
+ {
+ if (XLogRecHasBlockImage(record, block_id))
+ fpi_len += BLCKSZ - record->blocks[block_id].hole_length;
+ }
+
+ /* Update per-rmgr statistics */
stats->rmgr_stats[rmid].count++;
stats->rmgr_stats[rmid].rec_len += rec_len;
--
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