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Add show_data option to pg_get_wal_block_info.

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Allow users to opt out of returning FPI data and block data from
pg_get_wal_block_info as an optimization.  Testing has shown that this
can make function execution over twice as fast in some cases.

When pg_get_wal_block_info is called with "show_data := false", it
always returns NULL values for its block_data and block_fpi_data bytea
output parameters.  Nothing else changes.  In particular, the function
will still return the usual per-block summary of block data/FPI space
overhead.  Use of "show_data := false" is therefore feasible with all
queries that don't specifically require these raw binary strings.

Follow-up to recent work in commit 122376f0.  There still hasn't been a
stable release with the pg_get_wal_block_info function, so no bump in
the pg_walinspect extension version.

Per suggestion from Melanie Plageman.

Author: Peter Geoghegan <pg@bowt.ie>
Discussion: https://postgr.es/m/CAAKRu_bJvbcYBRj2cN6G2xV7B7-Ja+pjTO1nEnEhRR8OXYiABA@mail.gmail.com
Discussion: https://postgr.es/m/CAH2-Wzm9shOkEDM10_+qOZkRSQhKVxwBFiehH6EHWQQRd_rDPw@mail.gmail.com
This commit is contained in:
Peter Geoghegan
2023-03-31 14:02:52 -07:00
parent 6ee30209a6
commit df4f3ab517
6 changed files with 39 additions and 24 deletions
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13
contrib/pg_walinspect/pg_walinspect.c
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@@ -59,7 +59,8 @@ static void GetWalStats(FunctionCallInfo fcinfo,
XLogRecPtr start_lsn,
XLogRecPtr end_lsn,
bool stats_per_record);
static void GetWALBlockInfo(FunctionCallInfo fcinfo, XLogReaderState *record);
static void GetWALBlockInfo(FunctionCallInfo fcinfo, XLogReaderState *record,
bool show_data);
/*
* Return the LSN up to which the server has WAL.
@@ -244,7 +245,8 @@ GetWALRecordInfo(XLogReaderState *record, Datum *values,
* Keep this in sync with GetWALRecordInfo.
*/
static void
GetWALBlockInfo(FunctionCallInfo fcinfo, XLogReaderState *record)
GetWALBlockInfo(FunctionCallInfo fcinfo, XLogReaderState *record,
bool show_data)
{
#define PG_GET_WAL_BLOCK_INFO_COLS 20
int block_id;
@@ -359,7 +361,7 @@ GetWALBlockInfo(FunctionCallInfo fcinfo, XLogReaderState *record)
nulls[i++] = true;
/* block_data output */
if (blk->has_data)
if (blk->has_data && show_data)
{
bytea *block_data;
@@ -372,7 +374,7 @@ GetWALBlockInfo(FunctionCallInfo fcinfo, XLogReaderState *record)
nulls[i++] = true;
/* block_fpi_data output */
if (blk->has_image)
if (blk->has_image && show_data)
{
PGAlignedBlock buf;
Page page;
@@ -410,6 +412,7 @@ pg_get_wal_block_info(PG_FUNCTION_ARGS)
{
XLogRecPtr start_lsn = PG_GETARG_LSN(0);
XLogRecPtr end_lsn = PG_GETARG_LSN(1);
bool show_data = PG_GETARG_BOOL(2);
XLogReaderState *xlogreader;
MemoryContext old_cxt;
MemoryContext tmp_cxt;
@@ -435,7 +438,7 @@ pg_get_wal_block_info(PG_FUNCTION_ARGS)
/* Use the tmp context so we can clean up after each tuple is done */
old_cxt = MemoryContextSwitchTo(tmp_cxt);
GetWALBlockInfo(fcinfo, xlogreader);
GetWALBlockInfo(fcinfo, xlogreader, show_data);
/* clean up and switch back */
MemoryContextSwitchTo(old_cxt);