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<!-- doc/src/sgml/pgwalinspect.sgml -->
<sect1 id="pgwalinspect" xreflabel="pg_walinspect">
<title>pg_walinspect</title>
<indexterm zone="pgwalinspect">
<primary>pg_walinspect</primary>
</indexterm>
<para>
The <filename>pg_walinspect</filename> module provides SQL functions that
allow you to inspect the contents of write-ahead log of
a running <productname>PostgreSQL</productname> database cluster at a low
level, which is useful for debugging or analytical or reporting or
educational purposes. It is similar to <xref linkend="pgwaldump"/>, but
accessible through SQL rather than a separate utility.
</para>
<para>
All the functions of this module will provide the WAL information using the
current server's timeline ID.
</para>
<para>
All the functions of this module will try to find the first valid WAL record
that is at or after the given <replaceable>in_lsn</replaceable> or
<replaceable>start_lsn</replaceable> and will emit error if no such record
is available. Similarly, the <replaceable>end_lsn</replaceable> must be
available, and if it falls in the middle of a record, the entire record must
be available.
</para>
<note>
<para>
Some functions, such as <function><link
linkend="pg-logical-emit-message">pg_logical_emit_message</link></function>,
return the LSN <emphasis>after</emphasis> the record just
inserted. Therefore, if you pass that LSN as
<replaceable>in_lsn</replaceable> or <replaceable>start_lsn</replaceable>
to one of these functions, it will return the <emphasis>next</emphasis>
record.
</para>
</note>
<para>
By default, use of these functions is restricted to superusers and members of
the <literal>pg_read_server_files</literal> role. Access may be granted by
superusers to others using <command>GRANT</command>.
</para>
<sect2>
<title>General Functions</title>
<variablelist>
<varlistentry>
<term>
<function>
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)
</function>
</term>
<listitem>
<para>
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.
</para>
</listitem>
</varlistentry>
<varlistentry>
<term>
<function>
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
</function>
</term>
<listitem>
<para>
Gets information of all the valid WAL records between
<replaceable>start_lsn</replaceable> and <replaceable>end_lsn</replaceable>.
Returns one row per WAL record. If <replaceable>start_lsn</replaceable>
or <replaceable>end_lsn</replaceable> are not yet available, the
function will raise an error. For example, usage of the function is as
follows:
<screen>
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)
</screen>
</para>
</listitem>
</varlistentry>
<varlistentry>
<term>
<function>
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
</function>
</term>
<listitem>
<para>
This function is same as <function>pg_get_wal_records_info()</function>
except that it gets information of all the valid WAL records from
<replaceable>start_lsn</replaceable> till the end of WAL.
</para>
</listitem>
</varlistentry>
<varlistentry>
<term>
<function>
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
</function>
</term>
<listitem>
<para>
Gets statistics of all the valid WAL records between
<replaceable>start_lsn</replaceable> and
<replaceable>end_lsn</replaceable>. By default, it returns one row per
<replaceable>resource_manager</replaceable> type. When
<replaceable>per_record</replaceable> is set to <literal>true</literal>,
it returns one row per <replaceable>record_type</replaceable>.
If <replaceable>start_lsn</replaceable>
or <replaceable>end_lsn</replaceable> are not yet available, the
function will raise an error. For example, usage of the function is as
follows:
<screen>
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)
</screen>
With <replaceable>per_record</replaceable> passed as <literal>true</literal>:
<screen>
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)
</screen>
</para>
</listitem>
</varlistentry>
<varlistentry>
<term>
<function>
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
</function>
</term>
<listitem>
<para>
This function is same as <function>pg_get_wal_stats()</function> except
that it gets statistics of all the valid WAL records from
<replaceable>start_lsn</replaceable> till end of WAL.
</para>
</listitem>
</varlistentry>
</variablelist>
</sect2>
<sect2>
<title>Author</title>
<para>
Bharath Rupireddy <email>[email protected]</email>
</para>
</sect2>
</sect1>
|
