276 lines
16 KiB
Plaintext
276 lines
16 KiB
Plaintext
<!-- doc/src/sgml/pgwalinspect.sgml -->
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<sect1 id="pgwalinspect" xreflabel="pg_walinspect">
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<title>pg_walinspect</title>
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<indexterm zone="pgwalinspect">
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<primary>pg_walinspect</primary>
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</indexterm>
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<para>
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The <filename>pg_walinspect</filename> module provides SQL functions that
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allow you to inspect the contents of write-ahead log of
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a running <productname>PostgreSQL</productname> database cluster at a low
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level, which is useful for debugging or analytical or reporting or
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educational purposes. It is similar to <xref linkend="pgwaldump"/>, but
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accessible through SQL rather than a separate utility.
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</para>
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<para>
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All the functions of this module will provide the WAL information using the
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current server's timeline ID.
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</para>
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<para>
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All the functions of this module will try to find the first valid WAL record
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that is at or after the given <replaceable>in_lsn</replaceable> or
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<replaceable>start_lsn</replaceable> and will emit error if no such record
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is available. Similarly, the <replaceable>end_lsn</replaceable> must be
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available, and if it falls in the middle of a record, the entire record must
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be available.
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</para>
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<note>
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<para>
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Some functions, such as <function><link
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linkend="pg-logical-emit-message">pg_logical_emit_message</link></function>,
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return the LSN <emphasis>after</emphasis> the record just
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inserted. Therefore, if you pass that LSN as
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<replaceable>in_lsn</replaceable> or <replaceable>start_lsn</replaceable>
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to one of these functions, it will return the <emphasis>next</emphasis>
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record.
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</para>
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</note>
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<para>
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By default, use of these functions is restricted to superusers and members of
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the <literal>pg_read_server_files</literal> role. Access may be granted by
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superusers to others using <command>GRANT</command>.
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</para>
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<sect2>
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<title>General Functions</title>
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<variablelist>
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<varlistentry>
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<term>
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<function>
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pg_get_wal_record_info(in_lsn pg_lsn,
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start_lsn OUT pg_lsn,
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end_lsn OUT pg_lsn,
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prev_lsn OUT pg_lsn,
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xid OUT xid,
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resource_manager OUT text,
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record_type OUT text,
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record_length OUT int4,
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main_data_length OUT int4,
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fpi_length OUT int4,
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description OUT text,
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block_ref OUT text)
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</function>
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</term>
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<listitem>
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<para>
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Gets WAL record information of a given LSN. If the given LSN isn't
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at the start of a WAL record, it gives the information of the next
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available valid WAL record; or an error if no such record is found.
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</para>
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</listitem>
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</varlistentry>
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<varlistentry>
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<term>
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<function>
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pg_get_wal_records_info(start_lsn pg_lsn,
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end_lsn pg_lsn,
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start_lsn OUT pg_lsn,
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end_lsn OUT pg_lsn,
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prev_lsn OUT pg_lsn,
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xid OUT xid,
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resource_manager OUT text,
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record_type OUT text,
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record_length OUT int4,
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main_data_length OUT int4,
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fpi_length OUT int4,
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description OUT text,
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block_ref OUT text)
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returns setof record
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</function>
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</term>
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<listitem>
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<para>
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Gets information of all the valid WAL records between
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<replaceable>start_lsn</replaceable> and <replaceable>end_lsn</replaceable>.
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Returns one row per WAL record. If <replaceable>start_lsn</replaceable>
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or <replaceable>end_lsn</replaceable> are not yet available, the
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function will raise an error. For example, usage of the function is as
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follows:
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<screen>
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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');
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start_lsn | end_lsn | prev_lsn | xid | resource_manager | record_type | record_length | main_data_length | fpi_length | description
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-----------+-----------+-----------+-----+------------------+--------------+---------------+------------------+------------+---------------------
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0/14FA118 | 0/14FB4B0 | 0/14F9958 | 725 | Btree | INSERT_LEAF | 5013 | 2 | 4960 | off 246
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0/14FB4B0 | 0/14FD050 | 0/14FA118 | 725 | Btree | INSERT_LEAF | 7045 | 2 | 6992 | off 130
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0/14FD050 | 0/14FD0A8 | 0/14FB4B0 | 725 | Heap2 | MULTI_INSERT | 85 | 6 | 0 | 1 tuples flags 0x02
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0/14FD0A8 | 0/14FD0F0 | 0/14FD050 | 725 | Btree | INSERT_LEAF | 72 | 2 | 0 | off 155
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0/14FD0F0 | 0/14FD138 | 0/14FD0A8 | 725 | Btree | INSERT_LEAF | 72 | 2 | 0 | off 134
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0/14FD138 | 0/14FD210 | 0/14FD0F0 | 725 | Heap | INSERT | 211 | 3 | 0 | off 11 flags 0x00
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0/14FD210 | 0/14FD250 | 0/14FD138 | 725 | Btree | INSERT_LEAF | 64 | 2 | 0 | off 246
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0/14FD250 | 0/14FF260 | 0/14FD210 | 725 | Btree | INSERT_LEAF | 8181 | 2 | 8128 | off 47
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0/14FF260 | 0/14FF2B8 | 0/14FD250 | 725 | Heap2 | MULTI_INSERT | 85 | 6 | 0 | 1 tuples flags 0x02
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0/14FF2B8 | 0/14FF300 | 0/14FF260 | 725 | Btree | INSERT_LEAF | 72 | 2 | 0 | off 155
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0/14FF300 | 0/15008D8 | 0/14FF2B8 | 725 | Btree | INSERT_LEAF | 5565 | 2 | 5512 | off 106
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0/15008D8 | 0/1500C48 | 0/14FF300 | 725 | Heap | INSERT | 874 | 3 | 820 | off 2 flags 0x01
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(12 rows)
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</screen>
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</para>
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</listitem>
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</varlistentry>
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<varlistentry>
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<term>
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<function>
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pg_get_wal_records_info_till_end_of_wal(start_lsn pg_lsn,
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start_lsn OUT pg_lsn,
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end_lsn OUT pg_lsn,
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prev_lsn OUT pg_lsn,
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xid OUT xid,
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resource_manager OUT text,
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record_type OUT text,
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record_length OUT int4,
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main_data_length OUT int4,
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fpi_length OUT int4,
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description OUT text,
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block_ref OUT text)
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returns setof record
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</function>
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</term>
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<listitem>
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<para>
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This function is same as <function>pg_get_wal_records_info()</function>
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except that it gets information of all the valid WAL records from
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<replaceable>start_lsn</replaceable> till the end of WAL.
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</para>
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</listitem>
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</varlistentry>
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<varlistentry>
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<term>
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<function>
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pg_get_wal_stats(start_lsn pg_lsn,
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end_lsn pg_lsn,
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per_record boolean DEFAULT false,
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"resource_manager/record_type" OUT text,
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count OUT int8,
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count_percentage OUT float4,
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record_length OUT int8,
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record_length_percentage OUT float4,
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fpi_length OUT int8,
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fpi_length_percentage OUT float4,
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combined_size OUT int8,
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combined_size_percentage OUT float4)
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returns setof record
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</function>
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</term>
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<listitem>
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<para>
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Gets statistics of all the valid WAL records between
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<replaceable>start_lsn</replaceable> and
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<replaceable>end_lsn</replaceable>. By default, it returns one row per
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<replaceable>resource_manager</replaceable> type. When
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<replaceable>per_record</replaceable> is set to <literal>true</literal>,
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it returns one row per <replaceable>record_type</replaceable>.
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If <replaceable>start_lsn</replaceable>
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or <replaceable>end_lsn</replaceable> are not yet available, the
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function will raise an error. For example, usage of the function is as
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follows:
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<screen>
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postgres=# select * from pg_get_wal_stats('0/12FBA30', '0/15011D7') where count > 0;
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resource_manager/record_type | count | count_percentage | record_size | record_size_percentage | fpi_size | fpi_size_percentage | combined_size | combined_size_percentage
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------------------------------+-------+------------------+-------------+------------------------+----------+---------------------+---------------+--------------------------
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XLOG | 10 | 0.10871929 | 796 | 0.052369177 | 352 | 0.061031006 | 1148 | 0.054751817
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Transaction | 187 | 2.0330508 | 62773 | 4.1298623 | 0 | 0 | 62773 | 2.9938467
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Storage | 13 | 0.14133507 | 546 | 0.035921574 | 0 | 0 | 546 | 0.0260405
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Database | 2 | 0.021743858 | 84 | 0.005526396 | 0 | 0 | 84 | 0.0040062307
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Standby | 218 | 2.3700805 | 15908 | 1.0465941 | 0 | 0 | 15908 | 0.75870377
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Heap2 | 1897 | 20.624048 | 383916 | 25.257998 | 364472 | 63.193447 | 748388 | 35.693035
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Heap | 1318 | 14.329202 | 621390 | 40.88151 | 139660 | 24.214746 | 761050 | 36.29693
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Btree | 5553 | 60.37182 | 434565 | 28.590216 | 72272 | 12.530776 | 506837 | 24.17269
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(8 rows)
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</screen>
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With <replaceable>per_record</replaceable> passed as <literal>true</literal>:
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<screen>
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postgres=# select * from pg_get_wal_stats('0/14AFC30', '0/15011D7', true) where count > 0;
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resource_manager/record_type | count | count_percentage | record_size | record_size_percentage | fpi_size | fpi_size_percentage | combined_size | combined_size_percentage
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------------------------------+-------+------------------+-------------+------------------------+----------+---------------------+---------------+--------------------------
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XLOG/CHECKPOINT_SHUTDOWN | 1 | 0.32894737 | 114 | 0.22891566 | 0 | 0 | 114 | 0.03534489
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XLOG/CHECKPOINT_ONLINE | 4 | 1.3157895 | 456 | 0.91566265 | 0 | 0 | 456 | 0.14137957
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XLOG/NEXTOID | 1 | 0.32894737 | 30 | 0.060240965 | 0 | 0 | 30 | 0.009301287
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Transaction/COMMIT | 9 | 2.9605262 | 1173 | 2.3554218 | 0 | 0 | 1173 | 0.36368033
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Storage/CREATE | 1 | 0.32894737 | 42 | 0.084337346 | 0 | 0 | 42 | 0.0130218025
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Database/CREATE_FILE_COPY | 2 | 0.65789473 | 84 | 0.16867469 | 0 | 0 | 84 | 0.026043605
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Standby/RUNNING_XACTS | 6 | 1.9736842 | 316 | 0.6345382 | 0 | 0 | 316 | 0.09797356
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Standby/INVALIDATIONS | 45 | 14.802631 | 4018 | 8.068274 | 0 | 0 | 4018 | 1.2457525
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Heap2/PRUNE | 4 | 1.3157895 | 270 | 0.5421687 | 0 | 0 | 270 | 0.08371159
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Heap2/FREEZE_PAGE | 27 | 8.881579 | 20904 | 41.975903 | 0 | 0 | 20904 | 6.481137
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Heap2/VISIBLE | 29 | 9.539474 | 1756 | 3.5261045 | 73728 | 27.032736 | 75484 | 23.403278
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Heap2/MULTI_INSERT | 13 | 4.2763157 | 1049 | 2.1064258 | 12216 | 4.479057 | 13265 | 4.112719
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Heap/INSERT | 19 | 6.25 | 2324 | 4.6666665 | 43884 | 16.090284 | 46208 | 14.326463
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Heap/UPDATE | 7 | 2.3026316 | 511 | 1.0261045 | 54340 | 19.924028 | 54851 | 17.006165
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Heap/HOT_UPDATE | 11 | 3.618421 | 1134 | 2.2771084 | 468 | 0.17159452 | 1602 | 0.49668875
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Heap/LOCK | 8 | 2.631579 | 432 | 0.8674699 | 0 | 0 | 432 | 0.13393854
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Heap/INPLACE | 45 | 14.802631 | 9123 | 18.319277 | 16076 | 5.894345 | 25199 | 7.8127713
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Heap/UPDATE+INIT | 1 | 0.32894737 | 817 | 1.6405623 | 0 | 0 | 817 | 0.25330505
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Btree/INSERT_LEAF | 70 | 23.026316 | 5183 | 10.407631 | 72024 | 26.407955 | 77207 | 23.937483
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Btree/DEDUP | 1 | 0.32894737 | 64 | 0.12851405 | 0 | 0 | 64 | 0.019842746
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(20 rows)
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</screen>
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</para>
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</listitem>
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</varlistentry>
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<varlistentry>
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<term>
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<function>
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pg_get_wal_stats_till_end_of_wal(start_lsn pg_lsn,
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per_record boolean DEFAULT false,
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"resource_manager/record_type" OUT text,
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count OUT int8,
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count_percentage OUT float4,
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record_length OUT int8,
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record_length_percentage OUT float4,
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fpi_length OUT int8,
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fpi_length_percentage OUT float4,
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combined_size OUT int8,
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combined_size_percentage OUT float4)
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returns setof record
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</function>
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</term>
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<listitem>
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<para>
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This function is same as <function>pg_get_wal_stats()</function> except
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that it gets statistics of all the valid WAL records from
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<replaceable>start_lsn</replaceable> till end of WAL.
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</para>
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</listitem>
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</varlistentry>
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</variablelist>
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</sect2>
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<sect2>
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<title>Author</title>
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<para>
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Bharath Rupireddy <email>bharath.rupireddyforpostgres@gmail.com</email>
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</para>
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</sect2>
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</sect1>
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