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Allow configurable LZ4 TOAST compression.

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There is now a per-column COMPRESSION option which can be set to pglz
(the default, and the only option in up until now) or lz4. Or, if you
like, you can set the new default_toast_compression GUC to lz4, and
then that will be the default for new table columns for which no value
is specified. We don't have lz4 support in the PostgreSQL code, so
to use lz4 compression, PostgreSQL must be built --with-lz4.

In general, TOAST compression means compression of individual column
values, not the whole tuple, and those values can either be compressed
inline within the tuple or compressed and then stored externally in
the TOAST table, so those properties also apply to this feature.

Prior to this commit, a TOAST pointer has two unused bits as part of
the va_extsize field, and a compessed datum has two unused bits as
part of the va_rawsize field. These bits are unused because the length
of a varlena is limited to 1GB; we now use them to indicate the
compression type that was used. This means we only have bit space for
2 more built-in compresison types, but we could work around that
problem, if necessary, by introducing a new vartag_external value for
any further types we end up wanting to add. Hopefully, it won't be
too important to offer a wide selection of algorithms here, since
each one we add not only takes more coding but also adds a build
dependency for every packager. Nevertheless, it seems worth doing
at least this much, because LZ4 gets better compression than PGLZ
with less CPU usage.

It's possible for LZ4-compressed datums to leak into composite type
values stored on disk, just as it is for PGLZ. It's also possible for
LZ4-compressed attributes to be copied into a different table via SQL
commands such as CREATE TABLE AS or INSERT .. SELECT.  It would be
expensive to force such values to be decompressed, so PostgreSQL has
never done so. For the same reasons, we also don't force recompression
of already-compressed values even if the target table prefers a
different compression method than was used for the source data.  These
architectural decisions are perhaps arguable but revisiting them is
well beyond the scope of what seemed possible to do as part of this
project.  However, it's relatively cheap to recompress as part of
VACUUM FULL or CLUSTER, so this commit adjusts those commands to do
so, if the configured compression method of the table happens not to
match what was used for some column value stored therein.

Dilip Kumar. The original patches on which this work was based were
written by Ildus Kurbangaliev, and those were patches were based on
even earlier work by Nikita Glukhov, but the design has since changed
very substantially, since allow a potentially large number of
compression methods that could be added and dropped on a running
system proved too problematic given some of the architectural issues
mentioned above; the choice of which specific compression method to
add first is now different; and a lot of the code has been heavily
refactored.  More recently, Justin Przyby helped quite a bit with
testing and reviewing and this version also includes some code
contributions from him. Other design input and review from Tomas
Vondra, Álvaro Herrera, Andres Freund, Oleg Bartunov, Alexander
Korotkov, and me.

Discussion: http://postgr.es/m/20170907194236.4cefce96%40wp.localdomain
Discussion: http://postgr.es/m/CAFiTN-uUpX3ck%3DK0mLEk-G_kUQY%3DSNOTeqdaNRR9FMdQrHKebw%40mail.gmail.com
This commit is contained in:
Robert Haas
2021-03-19 15:10:38 -04:00
parent e589c4890b
commit bbe0a81db6
61 changed files with 2261 additions and 160 deletions
Download Patch File Download Diff File Expand all files Collapse all files

12
doc/src/sgml/catalogs.sgml
View File

@@ -1355,6 +1355,18 @@
</para></entry>
</row>
<row>
<entry role="catalog_table_entry"><para role="column_definition">
<structfield>attcompression</structfield> <type>char</type>
</para>
<para>
The current compression method of the column. If it is an invalid
compression method (<literal>'\0'</literal>) then column data will not
be compressed. Otherwise, <literal>'p'</literal> = pglz compression or
<literal>'l'</literal> = lz4 compression.
</para></entry>
</row>
<row>
<entry role="catalog_table_entry"><para role="column_definition">
<structfield>attacl</structfield> <type>aclitem[]</type>

18
doc/src/sgml/func.sgml
View File

@@ -25992,8 +25992,8 @@ postgres=# SELECT * FROM pg_walfile_name_offset(pg_stop_backup());
<para>
The functions shown in <xref linkend="functions-admin-dbsize"/> calculate
the disk space usage of database objects, or assist in presentation
of usage results.
All these functions return sizes measured in bytes. If an OID that does
or understanding of usage results. <literal>bigint</literal> results
are measured in bytes. If an OID that does
not represent an existing object is passed to one of these
functions, <literal>NULL</literal> is returned.
</para>
@@ -26028,6 +26028,20 @@ postgres=# SELECT * FROM pg_walfile_name_offset(pg_stop_backup());
</para></entry>
</row>
<row>
<entry role="func_table_entry"><para role="func_signature">
<indexterm>
<primary>pg_column_compression</primary>
</indexterm>
<function>pg_column_compression</function> ( <type>"any"</type> )
<returnvalue>integer</returnvalue>
</para>
<para>
Shows the compression algorithm that was used to compress a
an individual variable-length value.
</para></entry>
</row>
<row>
<entry role="func_table_entry"><para role="func_signature">
<indexterm>

16
doc/src/sgml/ref/alter_table.sgml
View File

@@ -54,6 +54,7 @@ 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_method</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 ]
@@ -103,6 +104,7 @@ WITH ( MODULUS <replaceable class="parameter">numeric_literal</replaceable>, REM
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_method</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 ]
@@ -383,6 +385,20 @@ WITH ( MODULUS <replaceable class="parameter">numeric_literal</replaceable>, REM
</listitem>
</varlistentry>
<varlistentry>
<term>
<literal>SET COMPRESSION <replaceable class="parameter">compression_method</replaceable></literal>
</term>
<listitem>
<para>
This sets the compression method for a column. The supported compression
methods are <literal>pglz</literal> and <literal>lz4</literal>.
<literal>lz4</literal> is available only if <literal>--with-lz4</literal>
was used when building <productname>PostgreSQL</productname>.
</para>
</listitem>
</varlistentry>
<varlistentry>
<term><literal>ADD <replaceable class="parameter">table_constraint</replaceable> [ NOT VALID ]</literal></term>
<listitem>

33
doc/src/sgml/ref/create_table.sgml
View File

@@ -22,7 +22,7 @@ PostgreSQL documentation
<refsynopsisdiv>
<synopsis>
CREATE [ [ GLOBAL | LOCAL ] { TEMPORARY | TEMP } | UNLOGGED ] TABLE [ IF NOT EXISTS ] <replaceable class="parameter">table_name</replaceable> ( [
{ <replaceable class="parameter">column_name</replaceable> <replaceable class="parameter">data_type</replaceable> [ COLLATE <replaceable>collation</replaceable> ] [ <replaceable class="parameter">column_constraint</replaceable> [ ... ] ]
{ <replaceable class="parameter">column_name</replaceable> <replaceable class="parameter">data_type</replaceable> [ COLLATE <replaceable>collation</replaceable> ] [ COMPRESSION <replaceable>compression_method</replaceable> ] [ <replaceable class="parameter">column_constraint</replaceable> [ ... ] ]
| <replaceable>table_constraint</replaceable>
| LIKE <replaceable>source_table</replaceable> [ <replaceable>like_option</replaceable> ... ] }
[, ... ]
@@ -288,6 +288,26 @@ WITH ( MODULUS <replaceable class="parameter">numeric_literal</replaceable>, REM
</listitem>
</varlistentry>
<varlistentry>
<term><literal>COMPRESSION <replaceable class="parameter">compression_method</replaceable></literal></term>
<listitem>
<para>
The <literal>COMPRESSION</literal> clause sets the compression method
for a column. Compression is supported only for variable-width data
types, and is used only for columns whose storage type is main or
extended. (See <xref linkend="sql-altertable"/> for information on
column storage types.) Setting this property for a partitioned table
has no direct effect, because such tables have no storage of their own,
but the configured value is inherited by newly-created partitions.
The supported compression methods are <literal>pglz</literal> and
<literal>lz4</literal>. <literal>lz4</literal> is available only if
<literal>--with-lz4</literal> was used when building
<productname>PostgreSQL</productname>. The default
is <literal>pglz</literal>.
</para>
</listitem>
</varlistentry>
<varlistentry>
<term><literal>INHERITS ( <replaceable>parent_table</replaceable> [, ... ] )</literal></term>
<listitem>
@@ -605,6 +625,17 @@ WITH ( MODULUS <replaceable class="parameter">numeric_literal</replaceable>, REM
</listitem>
</varlistentry>
<varlistentry>
<term><literal>INCLUDING COMPRESSION</literal></term>
<listitem>
<para>
Compression method of the columns will be copied. The default
behavior is to exclude compression methods, resulting in columns
having the default compression method.
</para>
</listitem>
</varlistentry>
<varlistentry>
<term><literal>INCLUDING CONSTRAINTS</literal></term>
<listitem>

11
doc/src/sgml/ref/psql-ref.sgml
View File

@@ -3863,6 +3863,17 @@ bar
</listitem>
</varlistentry>
<varlistentry>
<term><varname>HIDE_TOAST_COMPRESSION</varname></term>
<listitem>
<para>
If this variable is set to <literal>true</literal>, column
compression method details are not displayed. This is mainly
useful for regression tests.
</para>
</listitem>
</varlistentry>
<varlistentry>
<term><varname>HIDE_TABLEAM</varname></term>
<listitem>