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help / color / mirror / Atom feedFrom: Ildus Kurbangaliev <[email protected]>
Subject: [PATCH 8/8] Add documentation for custom compression methods
Date: Mon, 18 Jun 2018 16:00:43 +0300
Signed-off-by: Ildus Kurbangaliev <[email protected]>
---
doc/src/sgml/catalogs.sgml | 19 ++-
doc/src/sgml/compression-am.sgml | 178 +++++++++++++++++++++
doc/src/sgml/filelist.sgml | 1 +
doc/src/sgml/indexam.sgml | 2 +-
doc/src/sgml/postgres.sgml | 1 +
doc/src/sgml/ref/alter_table.sgml | 18 +++
doc/src/sgml/ref/create_access_method.sgml | 5 +-
doc/src/sgml/ref/create_table.sgml | 13 ++
doc/src/sgml/storage.sgml | 6 +-
9 files changed, 236 insertions(+), 7 deletions(-)
create mode 100644 doc/src/sgml/compression-am.sgml
diff --git a/doc/src/sgml/catalogs.sgml b/doc/src/sgml/catalogs.sgml
index 0fd792ff1a..c8551c2fc3 100644
--- a/doc/src/sgml/catalogs.sgml
+++ b/doc/src/sgml/catalogs.sgml
@@ -57,7 +57,7 @@
<row>
<entry><link linkend="catalog-pg-am"><structname>pg_am</structname></link></entry>
- <entry>index access methods</entry>
+ <entry>access methods</entry>
</row>
<row>
@@ -70,6 +70,11 @@
<entry>access method support functions</entry>
</row>
+ <row>
+ <entry><link linkend="catalog-pg-attr-compression"><structname>pg_attr_compression</structname></link></entry>
+ <entry>table columns compression relationships and options</entry>
+ </row>
+
<row>
<entry><link linkend="catalog-pg-attrdef"><structname>pg_attrdef</structname></link></entry>
<entry>column default values</entry>
@@ -587,8 +592,10 @@
The catalog <structname>pg_am</structname> stores information about
relation access methods. There is one row for each access method supported
by the system.
- Currently, only indexes have access methods. The requirements for index
- access methods are discussed in detail in <xref linkend="indexam"/>.
+ Currently, compression and index access methods are supported.
+ The requirements for index access methods are discussed in detail
+ in <xref linkend="indexam"/>, for compression access methods
+ could be found in <xref linkend="compression-am"/>.
</para>
<table>
@@ -892,6 +899,12 @@
</sect1>
+ <sect1 id="catalog-pg-attr-compression">
+ <title><structname>pg_attr_compression</structname></title>
+ <indexterm zone="catalog-pg-attr-compression">
+ <primary>pg_attr_compression</primary>
+ </indexterm>
+ </sect1>
<sect1 id="catalog-pg-attrdef">
<title><structname>pg_attrdef</structname></title>
diff --git a/doc/src/sgml/compression-am.sgml b/doc/src/sgml/compression-am.sgml
new file mode 100644
index 0000000000..e23d817910
--- /dev/null
+++ b/doc/src/sgml/compression-am.sgml
@@ -0,0 +1,178 @@
+<!-- doc/src/sgml/compression-am.sgml -->
+
+<chapter id="compression-am">
+ <title>Compression Access Methods</title>
+ <para>
+ <productname>PostgreSQL</productname> supports two internal
+ built-in compression methods (<literal>pglz</literal>
+ and <literal>zlib</literal>), and also allows to add more custom compression
+ methods through compression access methods interface.
+ </para>
+
+ <sect1 id="builtin-compression-methods">
+ <title>Built-in Compression Access Methods</title>
+ <para>
+ These compression access methods are included in
+ <productname>PostgreSQL</productname> and don't need any external extensions.
+ </para>
+ <table id="builtin-compression-methods-table">
+ <title>Built-in Compression Access Methods</title>
+ <tgroup cols="2">
+ <thead>
+ <row>
+ <entry>Name</entry>
+ <entry>Options</entry>
+ </row>
+ </thead>
+ <tbody>
+ <row>
+ <entry><literal>pglz</literal></entry>
+ <entry>
+ <literal>min_input_size (int)</literal>,
+ <literal>max_input_size (int)</literal>,
+ <literal>min_comp_rate (int)</literal>,
+ <literal>first_success_by (int)</literal>,
+ <literal>match_size_good (int)</literal>,
+ <literal>match_size_drop (int)</literal>
+ </entry>
+ </row>
+ <row>
+ <entry><literal>zlib</literal></entry>
+ <entry><literal>level (text)</literal>, <literal>dict (text)</literal></entry>
+ </row>
+ </tbody>
+ </tgroup>
+ </table>
+ <para>
+ Note that for <literal>zlib</literal> to work it should be installed in the
+ system and <productname>PostgreSQL</productname> should be compiled without
+ <literal>--without-zlib</literal> flag.
+ </para>
+ </sect1>
+
+ <sect1 id="compression-api">
+ <title>Basic API for compression methods</title>
+
+ <para>
+ Each compression access method is described by a row in the
+ <link linkend="catalog-pg-am"><structname>pg_am</structname></link>
+ system catalog. The <structname>pg_am</structname> entry
+ specifies a name and a <firstterm>handler function</firstterm> for the access
+ method. These entries can be created and deleted using the
+ <xref linkend="sql-create-access-method"/> and
+ <xref linkend="sql-drop-access-method"/> SQL commands.
+ </para>
+
+ <para>
+ A compression access method handler function must be declared to accept a
+ single argument of type <type>internal</type> and to return the
+ pseudo-type <type>compression_am_handler</type>. The argument is a dummy value that
+ simply serves to prevent handler functions from being called directly from
+ SQL commands. The result of the function must be a palloc'd struct of
+ type <structname>CompressionAmRoutine</structname>, which contains everything
+ that the core code needs to know to make use of the compression access method.
+ The <structname>CompressionAmRoutine</structname> struct, also called the access
+ method's <firstterm>API struct</firstterm>, contains pointers to support
+ functions for the access method. These support functions are plain C
+ functions and are not visible or callable at the SQL level.
+ The support functions are described in <xref linkend="compression-am-functions"/>.
+ </para>
+
+ <para>
+ The structure <structname>CompressionAmRoutine</structname> is defined thus:
+<programlisting>
+typedef struct CompressionAmRoutine
+{
+ NodeTag type;
+
+ cmcheck_function cmcheck; /* can be NULL */
+ cminitstate_function cminitstate; /* can be NULL */
+ cmcompress_function cmcompress;
+ cmcompress_function cmdecompress;
+} CompressionAmRoutine;
+</programlisting>
+ </para>
+ </sect1>
+ <sect1 id="compression-am-functions">
+ <title>Compression Access Method Functions</title>
+
+ <para>
+ The compression and auxiliary functions that an compression access
+ method must provide in <structname>CompressionAmRoutine</structname> are:
+ </para>
+
+ <para>
+<programlisting>
+void
+cmcheck (Form_pg_attribute att, List *options);
+</programlisting>
+ Called when an attribute is linked with compression access method. Could
+ be used to check compatibility with the attribute and other additional
+ checks.
+ </para>
+
+ <para>
+ Compression functions take special struct
+ <structname>CompressionAmOptions</structname> as first
+ parameter. This struct contains per backend cached state for each
+ attribute compression record. CompressionAmOptions is defined thus:
+
+<programlisting>
+typedef struct CompressionAmOptions
+{
+ Oid acoid; /* Oid of attribute compression */
+ Oid amoid; /* Oid of compression access method */
+ List *acoptions; /* Parsed options, used for comparison */
+ CompressionAmRoutine *amroutine; /* compression access method routine */
+
+ /* result of cminitstate function will be put here */
+ void *acstate;
+} CompressionAmOptions;
+</programlisting>
+ </para>
+
+ <para>
+ The <structfield>acstate</structfield> field is used to keep temporary state
+ between compression functions calls and stores the result of
+ <structfield>cminitstate</structfield> function. It could be useful to store
+ the parsed view of the compression options.
+ </para>
+
+ <para>
+ Note that any invalidation of <structname>pg_attr_compression</structname> relation
+ will cause all the cached <structfield>acstate</structfield> options cleared.
+ They will be recreated on the next compression functions calls.
+ </para>
+
+ <para>
+<programlisting>
+void *
+cminitstate (Oid acoid, List *options);
+</programlisting>
+ Called when <structname>CompressionAmOptions</structname> is being
+ initialized. Can return a pointer to memory that will be passed between
+ compression functions calls.
+ </para>
+
+ <para>
+<programlisting>
+struct varlena *
+cmcompress (CompressionAmOptions *cmoptions,
+ const struct varlena *value);
+</programlisting>
+ Function is used to compress varlena. Could return NULL if data is
+ incompressible. If it returns varlena bigger than original the core will
+ not use it.
+ </para>
+
+ <para>
+<programlisting>
+struct varlena *
+cmdecompress (CompressionAmOptions *cmoptions,
+ const struct varlena *value);
+</programlisting>
+ Function is used to decompress varlena.
+ </para>
+
+ </sect1>
+</chapter>
diff --git a/doc/src/sgml/filelist.sgml b/doc/src/sgml/filelist.sgml
index a03ea1427b..8f482a60dd 100644
--- a/doc/src/sgml/filelist.sgml
+++ b/doc/src/sgml/filelist.sgml
@@ -90,6 +90,7 @@
<!ENTITY brin SYSTEM "brin.sgml">
<!ENTITY planstats SYSTEM "planstats.sgml">
<!ENTITY indexam SYSTEM "indexam.sgml">
+<!ENTITY compression-am SYSTEM "compression-am.sgml">
<!ENTITY nls SYSTEM "nls.sgml">
<!ENTITY plhandler SYSTEM "plhandler.sgml">
<!ENTITY fdwhandler SYSTEM "fdwhandler.sgml">
diff --git a/doc/src/sgml/indexam.sgml b/doc/src/sgml/indexam.sgml
index 05102724ea..54110050d1 100644
--- a/doc/src/sgml/indexam.sgml
+++ b/doc/src/sgml/indexam.sgml
@@ -47,7 +47,7 @@
<title>Basic API Structure for Indexes</title>
<para>
- Each index access method is described by a row in the
+ Each index access method is described by a row with INDEX type in the
<link linkend="catalog-pg-am"><structname>pg_am</structname></link>
system catalog. The <structname>pg_am</structname> entry
specifies a name and a <firstterm>handler function</firstterm> for the access
diff --git a/doc/src/sgml/postgres.sgml b/doc/src/sgml/postgres.sgml
index 96d196d229..17f2cc98b3 100644
--- a/doc/src/sgml/postgres.sgml
+++ b/doc/src/sgml/postgres.sgml
@@ -251,6 +251,7 @@
&custom-scan;
&geqo;
&indexam;
+ &compression-am;
&generic-wal;
&btree;
&gist;
diff --git a/doc/src/sgml/ref/alter_table.sgml b/doc/src/sgml/ref/alter_table.sgml
index 0aa0f093f2..122a17c1cf 100644
--- a/doc/src/sgml/ref/alter_table.sgml
+++ b/doc/src/sgml/ref/alter_table.sgml
@@ -53,6 +53,7 @@ ALTER TABLE [ IF EXISTS ] <replaceable class="parameter">name</replaceable>
ALTER [ COLUMN ] <replaceable class="parameter">column_name</replaceable> SET ( <replaceable class="parameter">attribute_option</replaceable> = <replaceable class="parameter">value</replaceable> [, ... ] )
ALTER [ COLUMN ] <replaceable class="parameter">column_name</replaceable> RESET ( <replaceable class="parameter">attribute_option</replaceable> [, ... ] )
ALTER [ COLUMN ] <replaceable class="parameter">column_name</replaceable> SET STORAGE { PLAIN | EXTERNAL | EXTENDED | MAIN }
+ ALTER [ COLUMN ] <replaceable class="parameter">column_name</replaceable> SET COMPRESSION <replaceable class="parameter">compression_am</replaceable> [ WITH (<replaceable class="parameter">compression_am_options</replaceable>) ] [ PRESERVE (<replaceable class="parameter">compression_preserve_list</replaceable>) ]
ADD <replaceable class="parameter">table_constraint</replaceable> [ NOT VALID ]
ADD <replaceable class="parameter">table_constraint_using_index</replaceable>
ALTER CONSTRAINT <replaceable class="parameter">constraint_name</replaceable> [ DEFERRABLE | NOT DEFERRABLE ] [ INITIALLY DEFERRED | INITIALLY IMMEDIATE ]
@@ -350,6 +351,23 @@ WITH ( MODULUS <replaceable class="parameter">numeric_literal</replaceable>, REM
</listitem>
</varlistentry>
+ <varlistentry>
+ <term>
+ <literal>SET COMPRESSION <replaceable class="parameter">compression_method_name</replaceable> [ WITH (<replaceable class="parameter">compression_method_options</replaceable>) ] [ PRESERVE (<replaceable class="parameter">compression_preserve_list</replaceable>) ]</literal>
+ </term>
+ <listitem>
+ <para>
+ This form adds compression to a column. Compression access method should be
+ created with <xref linkend="sql-create-access-method"/>. If compression
+ method has options they could be specified with <literal>WITH</literal>
+ parameter. The PRESERVE list contains list of compression access methods
+ used on the column and determines which of them should be kept on the
+ column. Without PRESERVE or partial list of compression methods table
+ will be rewritten.
+ </para>
+ </listitem>
+ </varlistentry>
+
<varlistentry>
<term><literal>ADD <replaceable class="parameter">table_constraint</replaceable> [ NOT VALID ]</literal></term>
<listitem>
diff --git a/doc/src/sgml/ref/create_access_method.sgml b/doc/src/sgml/ref/create_access_method.sgml
index 851c5e63be..a35005aca3 100644
--- a/doc/src/sgml/ref/create_access_method.sgml
+++ b/doc/src/sgml/ref/create_access_method.sgml
@@ -61,7 +61,7 @@ CREATE ACCESS METHOD <replaceable class="parameter">name</replaceable>
<listitem>
<para>
This clause specifies the type of access method to define.
- Only <literal>INDEX</literal> is supported at present.
+ <literal>INDEX</literal> and <literal>COMPRESSION</literal> types are supported at present.
</para>
</listitem>
</varlistentry>
@@ -79,6 +79,9 @@ CREATE ACCESS METHOD <replaceable class="parameter">name</replaceable>
be <type>index_am_handler</type>. The C-level API that the handler
function must implement varies depending on the type of access method.
The index access method API is described in <xref linkend="indexam"/>.
+ For <literal>COMPRESSION</literal> access methods, the type must be
+ <type>compression_am_handler</type>. The compression access method API
+ is described in <xref linkend="compression-am"/>.
</para>
</listitem>
</varlistentry>
diff --git a/doc/src/sgml/ref/create_table.sgml b/doc/src/sgml/ref/create_table.sgml
index 22dbc07b23..66d94df3dd 100644
--- a/doc/src/sgml/ref/create_table.sgml
+++ b/doc/src/sgml/ref/create_table.sgml
@@ -65,6 +65,7 @@ CREATE [ [ GLOBAL | LOCAL ] { TEMPORARY | TEMP } | UNLOGGED ] TABLE [ IF NOT EXI
GENERATED { ALWAYS | BY DEFAULT } AS IDENTITY [ ( <replaceable>sequence_options</replaceable> ) ] |
UNIQUE <replaceable class="parameter">index_parameters</replaceable> |
PRIMARY KEY <replaceable class="parameter">index_parameters</replaceable> |
+ COMPRESSION <replaceable class="parameter">compression_access_method</replaceable> [ WITH (<replaceable class="parameter">compression_am_options</replaceable>) ] |
REFERENCES <replaceable class="parameter">reftable</replaceable> [ ( <replaceable class="parameter">refcolumn</replaceable> ) ] [ MATCH FULL | MATCH PARTIAL | MATCH SIMPLE ]
[ ON DELETE <replaceable class="parameter">referential_action</replaceable> ] [ ON UPDATE <replaceable class="parameter">referential_action</replaceable> ] }
[ DEFERRABLE | NOT DEFERRABLE ] [ INITIALLY DEFERRED | INITIALLY IMMEDIATE ]
@@ -920,6 +921,18 @@ WITH ( MODULUS <replaceable class="parameter">numeric_literal</replaceable>, REM
</listitem>
</varlistentry>
+ <varlistentry>
+ <term><literal>COMPRESSION <replaceable class="parameter">compression_access_method</replaceable> [ WITH (<replaceable class="parameter">compression_am_options</replaceable>) ]</literal></term>
+ <listitem>
+ <para>
+ This clause adds compression to a column. Compression method could be
+ created with <xref linkend="sql-create-access-method"/>. If compression
+ method has options they could be specified by <literal>WITH</literal>
+ parameter.
+ </para>
+ </listitem>
+ </varlistentry>
+
<varlistentry id="sql-createtable-exclude">
<term><literal>EXCLUDE [ USING <replaceable class="parameter">index_method</replaceable> ] ( <replaceable class="parameter">exclude_element</replaceable> WITH <replaceable class="parameter">operator</replaceable> [, ... ] ) <replaceable class="parameter">index_parameters</replaceable> [ WHERE ( <replaceable class="parameter">predicate</replaceable> ) ]</literal></term>
<listitem>
diff --git a/doc/src/sgml/storage.sgml b/doc/src/sgml/storage.sgml
index cbdad0c3fb..89a5889d0f 100644
--- a/doc/src/sgml/storage.sgml
+++ b/doc/src/sgml/storage.sgml
@@ -385,10 +385,12 @@ Further details appear in <xref linkend="storage-toast-inmemory"/>.
</para>
<para>
-The compression technique used for either in-line or out-of-line compressed
+The default compression technique used for either in-line or out-of-line compressed
data is a fairly simple and very fast member
of the LZ family of compression techniques. See
-<filename>src/common/pg_lzcompress.c</filename> for the details.
+<filename>src/common/pg_lzcompress.c</filename> for the details. Also custom
+compressions could be used. Look at <xref linkend="compression-am"/> for
+more information.
</para>
<sect2 id="storage-toast-ondisk">
--
2.20.1
--MP_/IoARF=uydinlHTRfc3S.uiA--
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