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<chapter id="GIN">

<title>GIN Indexes</title>

This is much the same advantage as using <acronym>GiST</acronym>.

</para>

<para>

The <acronym>GIN</acronym>

implementation in <productname>PostgreSQL</productname> is primarily

maintained by Teodor Sigaev and Oleg Bartunov, and there is more

information on their

<ulink url="http://www.sai.msu.su/~megera/oddmuse/index.cgi/Gin">website</ulink>.

</para>

<para>

The <acronym>GIN</acronym>

implementation in <productname>PostgreSQL</productname> is primarily

maintained by Teodor Sigaev and Oleg Bartunov. There is more

information about <acronym>GIN</acronym> on their

<ulink url="http://www.sai.msu.su/~megera/oddmuse/index.cgi/Gin">website</ulink>.

</para>

</sect1>

<sect1 id="gin-extensibility">

<variablelist>

<varlistentry>

<term>int compare(Datum a, Datum b)</term>

<term>int compare(Datum a, Datum b)</term>

<listitem>

<para>

Compares keys (not indexed values!) and returns an integer less than

StrategyNumber n)</term>

<listitem>

<para>

Returns an array of keys of the query to be executed. n contains

thestrategy number of the operation

(see <xreflinkend="xindex-strategies">).

Depending on n, query may bedifferent type.

Returns an array of keys of the query to be executed. n contains the

strategy number of the operation(see <xref

linkend="xindex-strategies">). Depending on n, query may be

different type.

</para>

</listitem>

</varlistentry>

<varlistentry>

<term>bool consistent(bool check[], StrategyNumber n, Datum query)</term>

<term>bool consistent(bool check[], StrategyNumber n, Datum query)</term>

<listitem>

<para>

Returns TRUE if the indexed value satisfies the query qualifier with

strategy n (or may satisfy in case of RECHECK mark in operator class).

Each element of the check array is TRUE if the indexed value has a

corresponding key in the query: if (check[i] == TRUE) the i-th key of

corresponding key in the query: if (check[i] == TRUE) the i-th key of

the query is present in the indexed value.

</para>

</listitem>

</sect1>

<sect1 id="gin-tips">

<title>GIN tips andtrics</title>

<title>GIN tips andtricks</title>

<variablelist>

<varlistentry>

<term>Create vs insert</term>

<listitem>

<para>

In most cases, insertion into <acronym>GIN</acronym> index is slow

In most cases, insertion intoa<acronym>GIN</acronym> index is slow

due to the likelihood of many keys being inserted for each value.

So, for bulk insertions into a table it is advisable to to drop the GIN

index and recreate it after finishing bulk insertion.

the whole result set, chosen at random.

</para>

<para>

"Soft" means that the actual number of returned results could slightly

differ from the specified limit, depending on the query and the quality

of the system's random number generator.

<quote>Soft</quote> means that the actual number of returned results

could slightlydiffer from the specified limit, depending on the query

and the qualityof the system's random number generator.

</para>

</listitem>

</varlistentry>

<para>

<acronym>GIN</acronym> doesn't support full index scans due to their

extremely inefficiency: because there are often many keys per value,

extreme inefficiency: because there are often many keys per value,

each heap pointer will returned several times.

</para>

<para>

WhenextractQuery returns zero keys, <acronym>GIN</acronym> will emit a

error: for different opclasses and strategies the semantic meaning of a void

but they don't overlap the void array), and <acronym>GIN</acronym> can't

suggest reasonable answer.

When<function>extractQuery</function> returns zero keys,

<acronym>GIN</acronym> will emit anerror: for different opclasses and

example, any array contains the void array, but they don't overlap the

void array), and <acronym>GIN</acronym> can'tsuggest a reasonable answer.

</para>

<para>