</thead>

<tbody>

<row>

<entry><link linkend="view-pg-aios"><structname>pg_aios</structname></link></entry>

<entry>In-use asynchronous IO handles</entry>

</row>

<row>

<entry><link linkend="view-pg-available-extensions"><structname>pg_available_extensions</structname></link></entry>

<entry>available extensions</entry>

</table>

</sect1>

<sect1 id="view-pg-aios">

<title><structname>pg_aios</structname></title>

<indexterm zone="view-pg-aios">

<primary>pg_aios</primary>

</indexterm>

<para>

The <structname>pg_aios</structname> view lists all <xref

linkend="glossary-aio"/> handles that are currently in-use. An I/O handle

is used to reference an I/O operation that is being prepared, executed or

is in the process of completing. <structname>pg_aios</structname> contains

one row for each I/O handle.

</para>

<para>

This view is mainly useful for developers of

<productname>PostgreSQL</productname>, but may also be useful when tuning

<productname>PostgreSQL</productname>.

</para>

<table>

<title><structname>pg_aios</structname> Columns</title>

<tgroup cols="1">

<thead>

<row>

<entry role="catalog_table_entry"><para role="column_definition">

Column Type

</para>

<para>

Description

</para></entry>

</row>

</thead>

<tbody>

<row>

<entry role="catalog_table_entry"><para role="column_definition">

<structfield>pid</structfield> <type>int4</type>

</para>

<para>

Process ID of the server process that is issuing this I/O.

</para></entry>

</row>

<row>

<entry role="catalog_table_entry"><para role="column_definition">

<structfield>io_id</structfield> <type>int4</type>

</para>

<para>

Identifier of the I/O handle. Handles are reused once the I/O

completed (or if the handle is released before I/O is started). On reuse

<link linkend="view-pg-aios-io-generation">

<structname>pg_aios</structname>.<structfield>io_generation</structfield>

</link>

is incremented.

</para></entry>

</row>

<row>

<entry role="catalog_table_entry" id="view-pg-aios-io-generation"><para role="column_definition">

<structfield>io_generation</structfield> <type>int8</type>

</para>

<para>

Generation of the I/O handle.

</para></entry>

</row>

<row>

<entry role="catalog_table_entry"><para role="column_definition">

<structfield>state</structfield> <type>text</type>

</para>

<para>

State of the I/O handle:

<itemizedlist>

<listitem>

<para>

<literal>HANDED_OUT</literal>, referenced by code but not yet used

</para>

</listitem>

<listitem>

<para>

<literal>DEFINED</literal>, information necessary for execution is known

</para>

</listitem>

<listitem>

<para>

<literal>STAGED</literal>, ready for execution

</para>

</listitem>

<listitem>

<para>

<literal>SUBMITTED</literal>, submitted for execution

</para>

</listitem>

<listitem>

<para>

<literal>COMPLETED_IO</literal>, finished, but result has not yet been processed

</para>

</listitem>

<listitem>

<para>

<literal>COMPLETED_SHARED</literal>, shared completion processing completed

</para>

</listitem>

<listitem>

<para>

<literal>COMPLETED_LOCAL</literal>, backend local completion processing completed

</para>

</listitem>

</itemizedlist>

</para></entry>

</row>

<row>

<entry role="catalog_table_entry"><para role="column_definition">

<structfield>operation</structfield> <type>text</type>

</para>

<para>

Operation performed using the I/O handle:

<itemizedlist>

<listitem>

<para>

<literal>invalid</literal>, not yet known

</para>

</listitem>

<listitem>

<para>

<literal>readv</literal>, a vectored read

</para>

</listitem>

<listitem>

<para>

<literal>writev</literal>, a vectored write

</para>

</listitem>

</itemizedlist>

</para></entry>

</row>

<row>

<entry role="catalog_table_entry"><para role="column_definition">

<structfield>off</structfield> <type>int8</type>

</para>

<para>

Offset of the I/O operation.

</para></entry>

</row>

<row>

<entry role="catalog_table_entry"><para role="column_definition">

<structfield>length</structfield> <type>int8</type>

</para>

<para>

Length of the I/O operation.

</para></entry>

</row>

<row>

<entry role="catalog_table_entry"><para role="column_definition">

<structfield>target</structfield> <type>text</type>

</para>

<para>

What kind of object is the I/O targeting:

<itemizedlist spacing="compact">

<listitem>

<para>

<literal>smgr</literal>, I/O on relations

</para>

</listitem>

</itemizedlist>

</para></entry>

</row>

<row>

<entry role="catalog_table_entry"><para role="column_definition">

<structfield>handle_data_len</structfield> <type>int2</type>

</para>

<para>

Length of the data associated with the I/O operation. For I/O to/from

<xref linkend="guc-shared-buffers"/> and <xref

linkend="guc-temp-buffers"/>, this indicates the number of buffers the

I/O is operating on.

</para></entry>

</row>

<row>

<entry role="catalog_table_entry"><para role="column_definition">

<structfield>raw_result</structfield> <type>int4</type>

</para>

<para>

Low-level result of the I/O operation, or NULL if the operation has not

yet completed.

</para></entry>

</row>

<row>

<entry role="catalog_table_entry"><para role="column_definition">

<structfield>result</structfield> <type>text</type>

</para>

<para>

High-level result of the I/O operation:

<itemizedlist>

<listitem>

<para>

<literal>UNKNOWN</literal> means that the result of the

operation is not yet known.

</para>

</listitem>

<listitem>

<para>

<literal>OK</literal> means the I/O completed successfully.

</para>

</listitem>

<listitem>

<para>

<literal>PARTIAL</literal> means that the I/O completed without

error, but did not process all data. Commonly callers will need to

retry and perform the remainder of the work in a separate I/O.

</para>

</listitem>

<listitem>

<para>

<literal>WARNING</literal> means that the I/O completed without

error, but that execution of the IO triggered a warning. E.g. when

encountering a corrupted buffer with <xref

linkend="guc-zero-damaged-pages"/> enabled.

</para>

</listitem>

<listitem>

<para>

<literal>ERROR</literal> means the I/O failed with an error.

</para>

</listitem>

</itemizedlist>

</para></entry>

</row>

<row>

<entry role="catalog_table_entry"><para role="column_definition">

<structfield>target_desc</structfield> <type>text</type>

</para>

<para>

Description of what the I/O operation is targeting.

</para></entry>

</row>

<row>

<entry role="catalog_table_entry"><para role="column_definition">

<structfield>f_sync</structfield> <type>bool</type>

</para>

<para>

Flag indicating whether the I/O is executed synchronously.

</para></entry>

</row>

<row>

<entry role="catalog_table_entry"><para role="column_definition">

<structfield>f_localmem</structfield> <type>bool</type>

</para>

<para>

Flag indicating whether the I/O references process local memory.

</para></entry>

</row>

<row>

<entry role="catalog_table_entry"><para role="column_definition">

<structfield>f_buffered</structfield> <type>bool</type>

</para>

<para>

Flag indicating whether the I/O is buffered I/O.

</para></entry>

</row>

</tbody>

</tgroup>

</table>

<para>

The <structname>pg_aios</structname> view is read-only.

</para>

<para>

By default, the <structname>pg_aios</structname> view can be read only by

superusers or roles with privileges of the

<literal>pg_read_all_stats</literal> role.

</para>

</sect1>

<sect1 id="view-pg-available-extensions">

<title><structname>pg_available_extensions</structname></title>

SELECT*FROM pg_get_wait_events();

SELECT*FROM pg_get_aios();

REVOKE ALLON pg_aiosFROM PUBLIC;

GRANTSELECTON pg_aios TO pg_read_all_stats;

REVOKE EXECUTEON FUNCTION pg_get_aios()FROM PUBLIC;

GRANT EXECUTEON FUNCTION pg_get_aios() TO pg_read_all_stats;

OBJS =\

aio.o\

aio_callback.o\

aio_funcs.o\

aio_init.o\

aio_io.o\

aio_target.o\