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<!-- doc/src/sgml/brin.sgml -->
<chapter id="BRIN">
<title>BRIN Indexes</title>
<indexterm>
<primary>index</primary>
<secondary>BRIN</secondary>
</indexterm>
<sect1 id="brin-intro">
<title>Introduction</title>
<para>
<acronym>BRIN</acronym> stands for Block Range Index.
<acronym>BRIN</acronym> is designed for handling very large tables
in which certain columns have some natural correlation with their
physical location within the table.
A <firstterm>block range</> is a group of pages that are physically
adjacent in the table; for each block range, some summary info is stored
by the index.
For example, a table storing a store's sale orders might have
a date column on which each order was placed, and most of the time
the entries for earlier orders will appear earlier in the table as well;
a table storing a ZIP code column might have all codes for a city
grouped together naturally.
</para>
<para>
<acronym>BRIN</acronym> indexes can satisfy queries via regular bitmap
index scans, and will return all tuples in all pages within each range if
the summary info stored by the index is <firstterm>consistent</> with the
query conditions.
The query executor is in charge of rechecking these tuples and discarding
those that do not match the query conditions — in other words, these
indexes are lossy.
Because a <acronym>BRIN</acronym> index is very small, scanning the index
adds little overhead compared to a sequential scan, but may avoid scanning
large parts of the table that are known not to contain matching tuples.
</para>
<para>
The specific data that a <acronym>BRIN</acronym> index will store,
as well as the specific queries that the index will be able to satisfy,
depend on the operator class selected for each column of the index.
Data types having a linear sort order can have operator classes that
store the minimum and maximum value within each block range, for instance;
geometrical types might store the bounding box for all the objects
in the block range.
</para>
<para>
The size of the block range is determined at index creation time by
the <literal>pages_per_range</> storage parameter. The number of index
entries will be equal to the size of the relation in pages divided by
the selected value for <literal>pages_per_range</>. Therefore, the smaller
the number, the larger the index becomes (because of the need to
store more index entries), but at the same time the summary data stored can
be more precise and more data blocks can be skipped during an index scan.
</para>
</sect1>
<sect1 id="brin-builtin-opclasses">
<title>Built-in Operator Classes</title>
<para>
The core <productname>PostgreSQL</productname> distribution
includes the <acronym>BRIN</acronym> operator classes shown in
<xref linkend="brin-builtin-opclasses-table">.
</para>
<para>
The <firstterm>minmax</>
operator classes store the minimum and the maximum values appearing
in the indexed column within the range. The <firstterm>inclusion</>
operator classes store a value which includes the values in the indexed
column within the range.
</para>
<table id="brin-builtin-opclasses-table">
<title>Built-in <acronym>BRIN</acronym> Operator Classes</title>
<tgroup cols="3">
<thead>
<row>
<entry>Name</entry>
<entry>Indexed Data Type</entry>
<entry>Indexable Operators</entry>
</row>
</thead>
<tbody>
<row>
<entry><literal>bytea_minmax_ops</literal></entry>
<entry><type>bytea</type></entry>
<entry>
<literal><</literal>
<literal><=</literal>
<literal>=</literal>
<literal>>=</literal>
<literal>></literal>
</entry>
</row>
<row>
<entry><literal>char_minmax_ops</literal></entry>
<entry><type>"char"</type></entry>
<entry>
<literal><</literal>
<literal><=</literal>
<literal>=</literal>
<literal>>=</literal>
<literal>></literal>
</entry>
</row>
<row>
<entry><literal>name_minmax_ops</literal></entry>
<entry><type>name</type></entry>
<entry>
<literal><</literal>
<literal><=</literal>
<literal>=</literal>
<literal>>=</literal>
<literal>></literal>
</entry>
</row>
<row>
<entry><literal>int8_minmax_ops</literal></entry>
<entry><type>bigint</type></entry>
<entry>
<literal><</literal>
<literal><=</literal>
<literal>=</literal>
<literal>>=</literal>
<literal>></literal>
</entry>
</row>
<row>
<entry><literal>int2_minmax_ops</literal></entry>
<entry><type>smallint</type></entry>
<entry>
<literal><</literal>
<literal><=</literal>
<literal>=</literal>
<literal>>=</literal>
<literal>></literal>
</entry>
</row>
<row>
<entry><literal>int4_minmax_ops</literal></entry>
<entry><type>integer</type></entry>
<entry>
<literal><</literal>
<literal><=</literal>
<literal>=</literal>
<literal>>=</literal>
<literal>></literal>
</entry>
</row>
<row>
<entry><literal>text_minmax_ops</literal></entry>
<entry><type>text</type></entry>
<entry>
<literal><</literal>
<literal><=</literal>
<literal>=</literal>
<literal>>=</literal>
<literal>></literal>
</entry>
</row>
<row>
<entry><literal>oid_minmax_ops</literal></entry>
<entry><type>oid</type></entry>
<entry>
<literal><</literal>
<literal><=</literal>
<literal>=</literal>
<literal>>=</literal>
<literal>></literal>
</entry>
</row>
<row>
<entry><literal>tid_minmax_ops</literal></entry>
<entry><type>tid</type></entry>
<entry>
<literal><</literal>
<literal><=</literal>
<literal>=</literal>
<literal>>=</literal>
<literal>></literal>
</entry>
</row>
<row>
<entry><literal>float4_minmax_ops</literal></entry>
<entry><type>real</type></entry>
<entry>
<literal><</literal>
<literal><=</literal>
<literal>=</literal>
<literal>>=</literal>
<literal>></literal>
</entry>
</row>
<row>
<entry><literal>float8_minmax_ops</literal></entry>
<entry><type>double precision</type></entry>
<entry>
<literal><</literal>
<literal><=</literal>
<literal>=</literal>
<literal>>=</literal>
<literal>></literal>
</entry>
</row>
<row>
<entry><literal>abstime_minmax_ops</literal></entry>
<entry><type>abstime</type></entry>
<entry>
<literal><</literal>
<literal><=</literal>
<literal>=</literal>
<literal>>=</literal>
<literal>></literal>
</entry>
</row>
<row>
<entry><literal>reltime_minmax_ops</literal></entry>
<entry><type>reltime</type></entry>
<entry>
<literal><</literal>
<literal><=</literal>
<literal>=</literal>
<literal>>=</literal>
<literal>></literal>
</entry>
</row>
<row>
<entry><literal>macaddr_minmax_ops</literal></entry>
<entry><type>macaddr</type></entry>
<entry>
<literal><</literal>
<literal><=</literal>
<literal>=</literal>
<literal>>=</literal>
<literal>></literal>
</entry>
</row>
<row>
<entry><literal>inet_minmax_ops</literal></entry>
<entry><type>inet</type></entry>
<entry>
<literal><</literal>
<literal><=</literal>
<literal>=</literal>
<literal>>=</literal>
<literal>></literal>
</entry>
</row>
<row>
<entry><literal>inet_inclusion_ops</literal></entry>
<entry><type>inet</type></entry>
<entry>
<literal>&&</>
<literal>>></>
<literal>>>=</>
<literal><<</literal>
<literal><<=</literal>
<literal>=</literal>
</entry>
</row>
<row>
<entry><literal>bpchar_minmax_ops</literal></entry>
<entry><type>character</type></entry>
<entry>
<literal><</literal>
<literal><=</literal>
<literal>=</literal>
<literal>>=</literal>
<literal>></literal>
</entry>
</row>
<row>
<entry><literal>date_minmax_ops</literal></entry>
<entry><type>date</type></entry>
<entry>
<literal><</literal>
<literal><=</literal>
<literal>=</literal>
<literal>>=</literal>
<literal>></literal>
</entry>
</row>
<row>
<entry><literal>time_minmax_ops</literal></entry>
<entry><type>time without time zone</type></entry>
<entry>
<literal><</literal>
<literal><=</literal>
<literal>=</literal>
<literal>>=</literal>
<literal>></literal>
</entry>
</row>
<row>
<entry><literal>timestamp_minmax_ops</literal></entry>
<entry><type>timestamp without time zone</type></entry>
<entry>
<literal><</literal>
<literal><=</literal>
<literal>=</literal>
<literal>>=</literal>
<literal>></literal>
</entry>
</row>
<row>
<entry><literal>timestamptz_minmax_ops</literal></entry>
<entry><type>timestamp with time zone</type></entry>
<entry>
<literal><</literal>
<literal><=</literal>
<literal>=</literal>
<literal>>=</literal>
<literal>></literal>
</entry>
</row>
<row>
<entry><literal>interval_minmax_ops</literal></entry>
<entry><type>interval</type></entry>
<entry>
<literal><</literal>
<literal><=</literal>
<literal>=</literal>
<literal>>=</literal>
<literal>></literal>
</entry>
</row>
<row>
<entry><literal>timetz_minmax_ops</literal></entry>
<entry><type>time with time zone</type></entry>
<entry>
<literal><</literal>
<literal><=</literal>
<literal>=</literal>
<literal>>=</literal>
<literal>></literal>
</entry>
</row>
<row>
<entry><literal>bit_minmax_ops</literal></entry>
<entry><type>bit</type></entry>
<entry>
<literal><</literal>
<literal><=</literal>
<literal>=</literal>
<literal>>=</literal>
<literal>></literal>
</entry>
</row>
<row>
<entry><literal>varbit_minmax_ops</literal></entry>
<entry><type>bit varying</type></entry>
<entry>
<literal><</literal>
<literal><=</literal>
<literal>=</literal>
<literal>>=</literal>
<literal>></literal>
</entry>
</row>
<row>
<entry><literal>numeric_minmax_ops</literal></entry>
<entry><type>numeric</type></entry>
<entry>
<literal><</literal>
<literal><=</literal>
<literal>=</literal>
<literal>>=</literal>
<literal>></literal>
</entry>
</row>
<row>
<entry><literal>uuid_minmax_ops</literal></entry>
<entry><type>uuid</type></entry>
<entry>
<literal><</literal>
<literal><=</literal>
<literal>=</literal>
<literal>>=</literal>
<literal>></literal>
</entry>
</row>
<row>
<entry><literal>range_inclusion_ops</></entry>
<entry><type>any range type</type></entry>
<entry>
<literal>&&</>
<literal>&></>
<literal>&<</>
<literal>>></>
<literal><<</>
<literal><@</>
<literal>=</>
<literal>@></>
<literal><</literal>
<literal><=</literal>
<literal>=</literal>
<literal>>=</literal>
<literal>></literal>
</entry>
</row>
<row>
<entry><literal>pg_lsn_minmax_ops</literal></entry>
<entry><type>pg_lsn</type></entry>
<entry>
<literal><</literal>
<literal><=</literal>
<literal>=</literal>
<literal>>=</literal>
<literal>></literal>
</entry>
</row>
<row>
<entry><literal>box_inclusion_ops</></entry>
<entry><type>box</type></entry>
<entry>
<literal>&&</>
<literal>&></>
<literal>&<</>
<literal>>></>
<literal><<</>
<literal><@</>
<literal>~=</>
<literal>@></>
<literal>&>|</>
<literal>|&<</>
<literal>>>|</>
<literal>|<<</literal>
</entry>
</row>
</tbody>
</tgroup>
</table>
</sect1>
<sect1 id="brin-extensibility">
<title>Extensibility</title>
<para>
The <acronym>BRIN</acronym> interface has a high level of abstraction,
requiring the access method implementer only to implement the semantics
of the data type being accessed. The <acronym>BRIN</acronym> layer
itself takes care of concurrency, logging and searching the index structure.
</para>
<para>
All it takes to get a <acronym>BRIN</acronym> access method working is to
implement a few user-defined methods, which define the behavior of
summary values stored in the index and the way they interact with
scan keys.
In short, <acronym>BRIN</acronym> combines
extensibility with generality, code reuse, and a clean interface.
</para>
<para>
There are four methods that an operator class for <acronym>BRIN</acronym>
must provide:
<variablelist>
<varlistentry>
<term><function>BrinOpcInfo *opcInfo(Oid type_oid)</></term>
<listitem>
<para>
Returns internal information about the indexed columns' summary data.
The return value must point to a palloc'd <structname>BrinOpcInfo</>,
which has this definition:
<programlisting>
typedef struct BrinOpcInfo
{
/* Number of columns stored in an index column of this opclass */
uint16 oi_nstored;
/* Opaque pointer for the opclass' private use */
void *oi_opaque;
/* Type cache entries of the stored columns */
TypeCacheEntry *oi_typcache[FLEXIBLE_ARRAY_MEMBER];
} BrinOpcInfo;
</programlisting>
<structname>BrinOpcInfo</>.<structfield>oi_opaque</> can be used by the
operator class routines to pass information between support procedures
during an index scan.
</para>
</listitem>
</varlistentry>
<varlistentry>
<term><function>bool consistent(BrinDesc *bdesc, BrinValues *column,
ScanKey key)</function></term>
<listitem>
<para>
Returns whether the ScanKey is consistent with the given indexed
values for a range.
The attribute number to use is passed as part of the scan key.
</para>
</listitem>
</varlistentry>
<varlistentry>
<term><function>bool addValue(BrinDesc *bdesc, BrinValues *column,
Datum newval, bool isnull)</function></term>
<listitem>
<para>
Given an index tuple and an indexed value, modifies the indicated
attribute of the tuple so that it additionally represents the new value.
If any modification was done to the tuple, <literal>true</literal> is
returned.
</para>
</listitem>
</varlistentry>
<varlistentry>
<term><function>bool unionTuples(BrinDesc *bdesc, BrinValues *a,
BrinValues *b)</function></term>
<listitem>
<para>
Consolidates two index tuples. Given two index tuples, modifies the
indicated attribute of the first of them so that it represents both tuples.
The second tuple is not modified.
</para>
</listitem>
</varlistentry>
</variablelist>
To implement these methods in a generic way, the operator class
defines its own internal support functions.
(For instance, <quote>min/max</> operator classes implements
support functions for the four inequality operators for the data type.)
Additionally, the operator class must supply appropriate
operator entries,
to enable the optimizer to use the index when those operators are
used in queries.
</para>
</sect1>
</chapter>
|
