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pg_walinspect: Add pg_get_wal_fpi_info()

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This function is able to extract the full page images from a range of
records, specified as of input arguments start_lsn and end_lsn.  Like
the other functions of this module, an error is returned if using LSNs
that do not reflect real system values.  All the FPIs stored in a single
record are extracted.

The module's version is bumped to 1.1.

Author: Bharath Rupireddy
Reviewed-by: Bertrand Drouvot
Discussion: https://postgr.es/m/CALj2ACVCcvzd7WiWvD=6_7NBvVB_r6G0EGSxL4F8vosAi6Se4g@mail.gmail.com
This commit is contained in:
Michael Paquier 2023-01-23 13:55:18 +09:00
parent 16fd03e956
commit c31cf1c03d
8 changed files with 245 additions and 4 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

2
contrib/pg_walinspect/Makefile
View File

@ -7,7 +7,7 @@ OBJS = \
PGFILEDESC = "pg_walinspect - functions to inspect contents of PostgreSQL Write-Ahead Log"
EXTENSION = pg_walinspect
DATA = pg_walinspect--1.0.sql
DATA = pg_walinspect--1.0.sql pg_walinspect--1.0--1.1.sql
REGRESS = pg_walinspect

44
contrib/pg_walinspect/expected/pg_walinspect.out
View File

@ -10,7 +10,7 @@ CREATE TABLE sample_tbl(col1 int, col2 int);
SELECT pg_current_wal_lsn() AS wal_lsn1 \gset
INSERT INTO sample_tbl SELECT * FROM generate_series(1, 2);
SELECT pg_current_wal_lsn() AS wal_lsn2 \gset
INSERT INTO sample_tbl SELECT * FROM generate_series(1, 2);
INSERT INTO sample_tbl SELECT * FROM generate_series(3, 4);
-- ===================================================================
-- Tests for input validation
-- ===================================================================
@ -73,6 +73,23 @@ SELECT COUNT(*) >= 1 AS ok FROM pg_get_wal_records_info(:'wal_lsn1', :'wal_lsn2'
t
(1 row)
-- ===================================================================
-- Tests to get full page image (FPI) from WAL record
-- ===================================================================
SELECT pg_current_wal_lsn() AS wal_lsn3 \gset
-- Force FPI on the next update.
CHECKPOINT;
-- Update table to generate an FPI.
UPDATE sample_tbl SET col1 = col1 * 100 WHERE col1 = 1;
SELECT pg_current_wal_lsn() AS wal_lsn4 \gset
-- Check if we get FPI from WAL record.
SELECT COUNT(*) >= 1 AS ok FROM pg_get_wal_fpi_info(:'wal_lsn3', :'wal_lsn4')
WHERE relfilenode = :'sample_tbl_oid';
ok
----
t
(1 row)
-- ===================================================================
-- Tests for permissions
-- ===================================================================
@ -98,6 +115,13 @@ SELECT has_function_privilege('regress_pg_walinspect',
f
(1 row)
SELECT has_function_privilege('regress_pg_walinspect',
'pg_get_wal_fpi_info(pg_lsn, pg_lsn) ', 'EXECUTE'); -- no
has_function_privilege
------------------------
f
(1 row)
-- Functions accessible by users with role pg_read_server_files
GRANT pg_read_server_files TO regress_pg_walinspect;
SELECT has_function_privilege('regress_pg_walinspect',
@ -121,6 +145,13 @@ SELECT has_function_privilege('regress_pg_walinspect',
t
(1 row)
SELECT has_function_privilege('regress_pg_walinspect',
'pg_get_wal_fpi_info(pg_lsn, pg_lsn) ', 'EXECUTE'); -- yes
has_function_privilege
------------------------
t
(1 row)
REVOKE pg_read_server_files FROM regress_pg_walinspect;
-- Superuser can grant execute to other users
GRANT EXECUTE ON FUNCTION pg_get_wal_record_info(pg_lsn)
@ -129,6 +160,8 @@ GRANT EXECUTE ON FUNCTION pg_get_wal_records_info(pg_lsn, pg_lsn)
TO regress_pg_walinspect;
GRANT EXECUTE ON FUNCTION pg_get_wal_stats(pg_lsn, pg_lsn, boolean)
TO regress_pg_walinspect;
GRANT EXECUTE ON FUNCTION pg_get_wal_fpi_info(pg_lsn, pg_lsn)
TO regress_pg_walinspect;
SELECT has_function_privilege('regress_pg_walinspect',
'pg_get_wal_record_info(pg_lsn)', 'EXECUTE'); -- yes
has_function_privilege
@ -150,12 +183,21 @@ SELECT has_function_privilege('regress_pg_walinspect',
t
(1 row)
SELECT has_function_privilege('regress_pg_walinspect',
'pg_get_wal_fpi_info(pg_lsn, pg_lsn) ', 'EXECUTE'); -- yes
has_function_privilege
------------------------
t
(1 row)
REVOKE EXECUTE ON FUNCTION pg_get_wal_record_info(pg_lsn)
FROM regress_pg_walinspect;
REVOKE EXECUTE ON FUNCTION pg_get_wal_records_info(pg_lsn, pg_lsn)
FROM regress_pg_walinspect;
REVOKE EXECUTE ON FUNCTION pg_get_wal_stats(pg_lsn, pg_lsn, boolean)
FROM regress_pg_walinspect;
REVOKE EXECUTE ON FUNCTION pg_get_wal_fpi_info(pg_lsn, pg_lsn)
FROM regress_pg_walinspect;
-- ===================================================================
-- Clean up
-- ===================================================================

1
contrib/pg_walinspect/meson.build
View File

@ -19,6 +19,7 @@ contrib_targets += pg_walinspect
install_data(
'pg_walinspect.control',
'pg_walinspect--1.0.sql',
'pg_walinspect--1.0--1.1.sql',
kwargs: contrib_data_args,
)

24
contrib/pg_walinspect/pg_walinspect--1.0--1.1.sql Normal file
View File

@ -0,0 +1,24 @@
/* contrib/pg_walinspect/pg_walinspect--1.0--1.1.sql */
-- complain if script is sourced in psql, rather than via ALTER EXTENSION
\echo Use "ALTER EXTENSION pg_walinspect UPDATE TO '1.1'" to load this file. \quit
--
-- pg_get_wal_fpi_info()
--
CREATE FUNCTION pg_get_wal_fpi_info(IN start_lsn pg_lsn,
IN end_lsn pg_lsn,
OUT lsn pg_lsn,
OUT reltablespace oid,
OUT reldatabase oid,
OUT relfilenode oid,
OUT relblocknumber int8,
OUT forkname text,
OUT fpi bytea
)
RETURNS SETOF record
AS 'MODULE_PATHNAME', 'pg_get_wal_fpi_info'
LANGUAGE C STRICT PARALLEL SAFE;
REVOKE EXECUTE ON FUNCTION pg_get_wal_fpi_info(pg_lsn, pg_lsn) FROM PUBLIC;
GRANT EXECUTE ON FUNCTION pg_get_wal_fpi_info(pg_lsn, pg_lsn) TO pg_read_server_files;

111
contrib/pg_walinspect/pg_walinspect.c
View File

@ -30,6 +30,7 @@
PG_MODULE_MAGIC;
PG_FUNCTION_INFO_V1(pg_get_wal_fpi_info);
PG_FUNCTION_INFO_V1(pg_get_wal_record_info);
PG_FUNCTION_INFO_V1(pg_get_wal_records_info);
PG_FUNCTION_INFO_V1(pg_get_wal_records_info_till_end_of_wal);
@ -55,6 +56,7 @@ static void FillXLogStatsRow(const char *name, uint64 n, uint64 total_count,
Datum *values, bool *nulls, uint32 ncols);
static void GetWalStats(FunctionCallInfo fcinfo, XLogRecPtr start_lsn,
XLogRecPtr end_lsn, bool stats_per_record);
static void GetWALFPIInfo(FunctionCallInfo fcinfo, XLogReaderState *record);
/*
* Check if the given LSN is in future. Also, return the LSN up to which the
@ -217,6 +219,115 @@ GetWALRecordInfo(XLogReaderState *record, Datum *values,
Assert(i == ncols);
}
/*
* Store a set of full page images from a single record.
*/
static void
GetWALFPIInfo(FunctionCallInfo fcinfo, XLogReaderState *record)
{
#define PG_GET_WAL_FPI_INFO_COLS 7
int block_id;
ReturnSetInfo *rsinfo = (ReturnSetInfo *) fcinfo->resultinfo;
for (block_id = 0; block_id <= XLogRecMaxBlockId(record); block_id++)
{
PGAlignedBlock buf;
Page page;
bytea *raw_page;
BlockNumber blk;
RelFileLocator rnode;
ForkNumber fork;
Datum values[PG_GET_WAL_FPI_INFO_COLS] = {0};
bool nulls[PG_GET_WAL_FPI_INFO_COLS] = {0};
int i = 0;
if (!XLogRecHasBlockRef(record, block_id))
continue;
if (!XLogRecHasBlockImage(record, block_id))
continue;
page = (Page) buf.data;
if (!RestoreBlockImage(record, block_id, page))
ereport(ERROR,
(errcode(ERRCODE_INTERNAL_ERROR),
errmsg_internal("%s", record->errormsg_buf)));
/* Full page exists, so let's save it. */
(void) XLogRecGetBlockTagExtended(record, block_id,
&rnode, &fork, &blk, NULL);
values[i++] = LSNGetDatum(record->ReadRecPtr);
values[i++] = ObjectIdGetDatum(rnode.spcOid);
values[i++] = ObjectIdGetDatum(rnode.dbOid);
values[i++] = ObjectIdGetDatum(rnode.relNumber);
values[i++] = Int64GetDatum((int64) blk);
if (fork >= 0 && fork <= MAX_FORKNUM)
values[i++] = CStringGetTextDatum(forkNames[fork]);
else
ereport(ERROR,
(errcode(ERRCODE_INTERNAL_ERROR),
errmsg_internal("invalid fork number: %u", fork)));
/* Initialize bytea buffer to copy the FPI to. */
raw_page = (bytea *) palloc(BLCKSZ + VARHDRSZ);
SET_VARSIZE(raw_page, BLCKSZ + VARHDRSZ);
/* Take a verbatim copy of the FPI. */
memcpy(VARDATA(raw_page), page, BLCKSZ);
values[i++] = PointerGetDatum(raw_page);
Assert(i == PG_GET_WAL_FPI_INFO_COLS);
tuplestore_putvalues(rsinfo->setResult, rsinfo->setDesc,
values, nulls);
}
#undef PG_GET_WAL_FPI_INFO_COLS
}
/*
* Get full page images with their relation information for all the WAL
* records between start and end LSNs. Decompression is applied to the
* blocks, if necessary.
*
* This function emits an error if a future start or end WAL LSN i.e. WAL LSN
* the database system doesn't know about is specified.
*/
Datum
pg_get_wal_fpi_info(PG_FUNCTION_ARGS)
{
XLogRecPtr start_lsn;
XLogRecPtr end_lsn;
XLogReaderState *xlogreader;
start_lsn = PG_GETARG_LSN(0);
end_lsn = PG_GETARG_LSN(1);
end_lsn = ValidateInputLSNs(false, start_lsn, end_lsn);
InitMaterializedSRF(fcinfo, 0);
xlogreader = InitXLogReaderState(start_lsn);
while (ReadNextXLogRecord(xlogreader) &&
xlogreader->EndRecPtr <= end_lsn)
{
GetWALFPIInfo(fcinfo, xlogreader);
CHECK_FOR_INTERRUPTS();
}
pfree(xlogreader->private_data);
XLogReaderFree(xlogreader);
PG_RETURN_VOID();
}
/*
* Get WAL record info.
*

2
contrib/pg_walinspect/pg_walinspect.control
View File

@ -1,5 +1,5 @@
# pg_walinspect extension
comment = 'functions to inspect contents of PostgreSQL Write-Ahead Log'
default_version = '1.0'
default_version = '1.1'
module_pathname = '$libdir/pg_walinspect'
relocatable = true

33
contrib/pg_walinspect/sql/pg_walinspect.sql
View File

@ -11,7 +11,7 @@ INSERT INTO sample_tbl SELECT * FROM generate_series(1, 2);
SELECT pg_current_wal_lsn() AS wal_lsn2 \gset
INSERT INTO sample_tbl SELECT * FROM generate_series(1, 2);
INSERT INTO sample_tbl SELECT * FROM generate_series(3, 4);
-- ===================================================================
-- Tests for input validation
@ -52,6 +52,22 @@ SELECT COUNT(*) >= 1 AS ok FROM pg_get_wal_records_info(:'wal_lsn1', :'wal_lsn2'
SELECT COUNT(*) >= 1 AS ok FROM pg_get_wal_records_info(:'wal_lsn1', :'wal_lsn2')
WHERE resource_manager = 'Heap' AND record_type = 'INSERT';
-- ===================================================================
-- Tests to get full page image (FPI) from WAL record
-- ===================================================================
SELECT pg_current_wal_lsn() AS wal_lsn3 \gset
-- Force FPI on the next update.
CHECKPOINT;
-- Update table to generate an FPI.
UPDATE sample_tbl SET col1 = col1 * 100 WHERE col1 = 1;
SELECT pg_current_wal_lsn() AS wal_lsn4 \gset
-- Check if we get FPI from WAL record.
SELECT COUNT(*) >= 1 AS ok FROM pg_get_wal_fpi_info(:'wal_lsn3', :'wal_lsn4')
WHERE relfilenode = :'sample_tbl_oid';
-- ===================================================================
-- Tests for permissions
-- ===================================================================
@ -66,6 +82,9 @@ SELECT has_function_privilege('regress_pg_walinspect',
SELECT has_function_privilege('regress_pg_walinspect',
'pg_get_wal_stats(pg_lsn, pg_lsn, boolean) ', 'EXECUTE'); -- no
SELECT has_function_privilege('regress_pg_walinspect',
'pg_get_wal_fpi_info(pg_lsn, pg_lsn) ', 'EXECUTE'); -- no
-- Functions accessible by users with role pg_read_server_files
GRANT pg_read_server_files TO regress_pg_walinspect;
@ -79,6 +98,9 @@ SELECT has_function_privilege('regress_pg_walinspect',
SELECT has_function_privilege('regress_pg_walinspect',
'pg_get_wal_stats(pg_lsn, pg_lsn, boolean) ', 'EXECUTE'); -- yes
SELECT has_function_privilege('regress_pg_walinspect',
'pg_get_wal_fpi_info(pg_lsn, pg_lsn) ', 'EXECUTE'); -- yes
REVOKE pg_read_server_files FROM regress_pg_walinspect;
-- Superuser can grant execute to other users
@ -91,6 +113,9 @@ GRANT EXECUTE ON FUNCTION pg_get_wal_records_info(pg_lsn, pg_lsn)
GRANT EXECUTE ON FUNCTION pg_get_wal_stats(pg_lsn, pg_lsn, boolean)
TO regress_pg_walinspect;
GRANT EXECUTE ON FUNCTION pg_get_wal_fpi_info(pg_lsn, pg_lsn)
TO regress_pg_walinspect;
SELECT has_function_privilege('regress_pg_walinspect',
'pg_get_wal_record_info(pg_lsn)', 'EXECUTE'); -- yes
@ -100,6 +125,9 @@ SELECT has_function_privilege('regress_pg_walinspect',
SELECT has_function_privilege('regress_pg_walinspect',
'pg_get_wal_stats(pg_lsn, pg_lsn, boolean) ', 'EXECUTE'); -- yes
SELECT has_function_privilege('regress_pg_walinspect',
'pg_get_wal_fpi_info(pg_lsn, pg_lsn) ', 'EXECUTE'); -- yes
REVOKE EXECUTE ON FUNCTION pg_get_wal_record_info(pg_lsn)
FROM regress_pg_walinspect;
@ -109,6 +137,9 @@ REVOKE EXECUTE ON FUNCTION pg_get_wal_records_info(pg_lsn, pg_lsn)
REVOKE EXECUTE ON FUNCTION pg_get_wal_stats(pg_lsn, pg_lsn, boolean)
FROM regress_pg_walinspect;
REVOKE EXECUTE ON FUNCTION pg_get_wal_fpi_info(pg_lsn, pg_lsn)
FROM regress_pg_walinspect;
-- ===================================================================
-- Clean up
-- ===================================================================

32
doc/src/sgml/pgwalinspect.sgml
View File

@ -188,6 +188,38 @@ combined_size_percentage | 2.8634072910530795
</listitem>
</varlistentry>
<varlistentry>
<term>
<function>pg_get_wal_fpi_info(start_lsn pg_lsn, end_lsn pg_lsn) returns setof record</function>
</term>
<listitem>
<para>
Gets a copy of full page images as <type>bytea</type> values (after
applying decompression when necessary) and their information associated
with all the valid WAL records between
<replaceable>start_lsn</replaceable> and
<replaceable>end_lsn</replaceable>. Returns one row per full page image.
If <replaceable>start_lsn</replaceable> or
<replaceable>end_lsn</replaceable> are not yet available, the function
will raise an error. For example:
<screen>
postgres=# SELECT lsn, reltablespace, reldatabase, relfilenode, relblocknumber,
forkname, substring(fpi for 24) as fpi_trimmed
FROM pg_get_wal_fpi_info('0/1801690', '0/1825C60');
-[ RECORD 1 ]--+---------------------------------------------------
lsn | 0/1807E20
reltablespace | 1663
reldatabase | 5
relfilenode | 16396
relblocknumber | 43
forkname | main
fpi_trimmed | \x00000000b89e660100000000a003c0030020042000000000
</screen>
</para>
</listitem>
</varlistentry>
</variablelist>
</sect2>