The pg_walinspect module provides SQL functions that
allow you to inspect the contents of write-ahead log of
a running PostgreSQL database cluster at a low
level, which is useful for debugging or analytical or reporting or
educational purposes. It is similar to pg_waldump, but
accessible through SQL rather than a separate utility.
All the functions of this module will provide the WAL information using the current server's timeline ID.
All the functions of this module will try to find the first valid WAL record
that is at or after the given in_lsn or
start_lsn and will emit error if no such record
is available. Similarly, the end_lsn must be
available, and if it falls in the middle of a record, the entire record must
be available.
Some functions, such as pg_logical_emit_message,
return the LSN after the record just
inserted. Therefore, if you pass that LSN as
in_lsn or start_lsn
to one of these functions, it will return the next
record.
By default, use of these functions is restricted to superusers and members of
the pg_read_server_files role. Access may be granted by
superusers to others using GRANT.
pg_get_wal_record_info(in_lsn pg_lsn,
start_lsn OUT pg_lsn,
end_lsn OUT pg_lsn,
prev_lsn OUT pg_lsn,
xid OUT xid,
resource_manager OUT text,
record_type OUT text,
record_length OUT int4,
main_data_length OUT int4,
fpi_length OUT int4,
description OUT text,
block_ref OUT text)
Gets WAL record information of a given LSN. If the given LSN isn't at the start of a WAL record, it gives the information of the next available valid WAL record; or an error if no such record is found.
pg_get_wal_records_info(start_lsn pg_lsn,
end_lsn pg_lsn,
start_lsn OUT pg_lsn,
end_lsn OUT pg_lsn,
prev_lsn OUT pg_lsn,
xid OUT xid,
resource_manager OUT text,
record_type OUT text,
record_length OUT int4,
main_data_length OUT int4,
fpi_length OUT int4,
description OUT text,
block_ref OUT text)
returns setof record
Gets information of all the valid WAL records between
start_lsn and end_lsn.
Returns one row per WAL record. If start_lsn
or end_lsn are not yet available, the
function will raise an error. For example, usage of the function is as
follows:
postgres=# select start_lsn, end_lsn, prev_lsn, xid, resource_manager, record_type, record_length, main_data_length, fpi_length, description from pg_get_wal_records_info('0/14F9A30', '0/15011D7');
start_lsn | end_lsn | prev_lsn | xid | resource_manager | record_type | record_length | main_data_length | fpi_length | description
-----------+-----------+-----------+-----+------------------+--------------+---------------+------------------+------------+---------------------
0/14FA118 | 0/14FB4B0 | 0/14F9958 | 725 | Btree | INSERT_LEAF | 5013 | 2 | 4960 | off 246
0/14FB4B0 | 0/14FD050 | 0/14FA118 | 725 | Btree | INSERT_LEAF | 7045 | 2 | 6992 | off 130
0/14FD050 | 0/14FD0A8 | 0/14FB4B0 | 725 | Heap2 | MULTI_INSERT | 85 | 6 | 0 | 1 tuples flags 0x02
0/14FD0A8 | 0/14FD0F0 | 0/14FD050 | 725 | Btree | INSERT_LEAF | 72 | 2 | 0 | off 155
0/14FD0F0 | 0/14FD138 | 0/14FD0A8 | 725 | Btree | INSERT_LEAF | 72 | 2 | 0 | off 134
0/14FD138 | 0/14FD210 | 0/14FD0F0 | 725 | Heap | INSERT | 211 | 3 | 0 | off 11 flags 0x00
0/14FD210 | 0/14FD250 | 0/14FD138 | 725 | Btree | INSERT_LEAF | 64 | 2 | 0 | off 246
0/14FD250 | 0/14FF260 | 0/14FD210 | 725 | Btree | INSERT_LEAF | 8181 | 2 | 8128 | off 47
0/14FF260 | 0/14FF2B8 | 0/14FD250 | 725 | Heap2 | MULTI_INSERT | 85 | 6 | 0 | 1 tuples flags 0x02
0/14FF2B8 | 0/14FF300 | 0/14FF260 | 725 | Btree | INSERT_LEAF | 72 | 2 | 0 | off 155
0/14FF300 | 0/15008D8 | 0/14FF2B8 | 725 | Btree | INSERT_LEAF | 5565 | 2 | 5512 | off 106
0/15008D8 | 0/1500C48 | 0/14FF300 | 725 | Heap | INSERT | 874 | 3 | 820 | off 2 flags 0x01
(12 rows)
pg_get_wal_records_info_till_end_of_wal(start_lsn pg_lsn,
start_lsn OUT pg_lsn,
end_lsn OUT pg_lsn,
prev_lsn OUT pg_lsn,
xid OUT xid,
resource_manager OUT text,
record_type OUT text,
record_length OUT int4,
main_data_length OUT int4,
fpi_length OUT int4,
description OUT text,
block_ref OUT text)
returns setof record
This function is same as pg_get_wal_records_info()
except that it gets information of all the valid WAL records from
start_lsn till the end of WAL.
pg_get_wal_stats(start_lsn pg_lsn,
end_lsn pg_lsn,
per_record boolean DEFAULT false,
"resource_manager/record_type" OUT text,
count OUT int8,
count_percentage OUT float8,
record_length OUT int8,
record_length_percentage OUT float8,
fpi_length OUT int8,
fpi_length_percentage OUT float8,
combined_size OUT int8,
combined_size_percentage OUT float8)
returns setof record
Gets statistics of all the valid WAL records between
start_lsn and
end_lsn. By default, it returns one row per
resource_manager type. When
per_record is set to true,
it returns one row per record_type.
If start_lsn
or end_lsn are not yet available, the
function will raise an error. For example, usage of the function is as
follows:
postgres=# select * from pg_get_wal_stats('0/12FBA30', '0/15011D7') where count > 0;
resource_manager/record_type | count | count_percentage | record_size | record_size_percentage | fpi_size | fpi_size_percentage | combined_size | combined_size_percentage
------------------------------+-------+------------------+-------------+------------------------+----------+---------------------+---------------+--------------------------
XLOG | 10 | 0.10871929 | 796 | 0.052369177 | 352 | 0.061031006 | 1148 | 0.054751817
Transaction | 187 | 2.0330508 | 62773 | 4.1298623 | 0 | 0 | 62773 | 2.9938467
Storage | 13 | 0.14133507 | 546 | 0.035921574 | 0 | 0 | 546 | 0.0260405
Database | 2 | 0.021743858 | 84 | 0.005526396 | 0 | 0 | 84 | 0.0040062307
Standby | 218 | 2.3700805 | 15908 | 1.0465941 | 0 | 0 | 15908 | 0.75870377
Heap2 | 1897 | 20.624048 | 383916 | 25.257998 | 364472 | 63.193447 | 748388 | 35.693035
Heap | 1318 | 14.329202 | 621390 | 40.88151 | 139660 | 24.214746 | 761050 | 36.29693
Btree | 5553 | 60.37182 | 434565 | 28.590216 | 72272 | 12.530776 | 506837 | 24.17269
(8 rows)
With per_record passed as true:
postgres=# select * from pg_get_wal_stats('0/14AFC30', '0/15011D7', true) where count > 0;
resource_manager/record_type | count | count_percentage | record_size | record_size_percentage | fpi_size | fpi_size_percentage | combined_size | combined_size_percentage
------------------------------+-------+------------------+-------------+------------------------+----------+---------------------+---------------+--------------------------
XLOG/CHECKPOINT_SHUTDOWN | 1 | 0.32894737 | 114 | 0.22891566 | 0 | 0 | 114 | 0.03534489
XLOG/CHECKPOINT_ONLINE | 4 | 1.3157895 | 456 | 0.91566265 | 0 | 0 | 456 | 0.14137957
XLOG/NEXTOID | 1 | 0.32894737 | 30 | 0.060240965 | 0 | 0 | 30 | 0.009301287
Transaction/COMMIT | 9 | 2.9605262 | 1173 | 2.3554218 | 0 | 0 | 1173 | 0.36368033
Storage/CREATE | 1 | 0.32894737 | 42 | 0.084337346 | 0 | 0 | 42 | 0.0130218025
Database/CREATE_FILE_COPY | 2 | 0.65789473 | 84 | 0.16867469 | 0 | 0 | 84 | 0.026043605
Standby/RUNNING_XACTS | 6 | 1.9736842 | 316 | 0.6345382 | 0 | 0 | 316 | 0.09797356
Standby/INVALIDATIONS | 45 | 14.802631 | 4018 | 8.068274 | 0 | 0 | 4018 | 1.2457525
Heap2/PRUNE | 4 | 1.3157895 | 270 | 0.5421687 | 0 | 0 | 270 | 0.08371159
Heap2/FREEZE_PAGE | 27 | 8.881579 | 20904 | 41.975903 | 0 | 0 | 20904 | 6.481137
Heap2/VISIBLE | 29 | 9.539474 | 1756 | 3.5261045 | 73728 | 27.032736 | 75484 | 23.403278
Heap2/MULTI_INSERT | 13 | 4.2763157 | 1049 | 2.1064258 | 12216 | 4.479057 | 13265 | 4.112719
Heap/INSERT | 19 | 6.25 | 2324 | 4.6666665 | 43884 | 16.090284 | 46208 | 14.326463
Heap/UPDATE | 7 | 2.3026316 | 511 | 1.0261045 | 54340 | 19.924028 | 54851 | 17.006165
Heap/HOT_UPDATE | 11 | 3.618421 | 1134 | 2.2771084 | 468 | 0.17159452 | 1602 | 0.49668875
Heap/LOCK | 8 | 2.631579 | 432 | 0.8674699 | 0 | 0 | 432 | 0.13393854
Heap/INPLACE | 45 | 14.802631 | 9123 | 18.319277 | 16076 | 5.894345 | 25199 | 7.8127713
Heap/UPDATE+INIT | 1 | 0.32894737 | 817 | 1.6405623 | 0 | 0 | 817 | 0.25330505
Btree/INSERT_LEAF | 70 | 23.026316 | 5183 | 10.407631 | 72024 | 26.407955 | 77207 | 23.937483
Btree/DEDUP | 1 | 0.32894737 | 64 | 0.12851405 | 0 | 0 | 64 | 0.019842746
(20 rows)
pg_get_wal_stats_till_end_of_wal(start_lsn pg_lsn,
per_record boolean DEFAULT false,
"resource_manager/record_type" OUT text,
count OUT int8,
count_percentage OUT float8,
record_length OUT int8,
record_length_percentage OUT float8,
fpi_length OUT int8,
fpi_length_percentage OUT float8,
combined_size OUT int8,
combined_size_percentage OUT float8)
returns setof record
This function is same as pg_get_wal_stats() except
that it gets statistics of all the valid WAL records from
start_lsn till end of WAL.
Bharath Rupireddy <bharath.rupireddyforpostgres@gmail.com>