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Simplify pg_am representation of ordering-capable access methods:

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provide just a boolean 'amcanorder', instead of fields that specify the
sort operator strategy numbers.  We have decided to require ordering-capable
AMs to use btree-compatible strategy numbers, so the old fields are
overkill (and indeed misleading about what's allowed).
This commit is contained in:
Tom Lane
2007-01-20 23:13:01 +00:00
parent c82cc604f5
commit fcf4b146c6
8 changed files with 58 additions and 80 deletions
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19
doc/src/sgml/catalogs.sgml
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@ -1,4 +1,4 @@
<!-- $PostgreSQL: pgsql/doc/src/sgml/catalogs.sgml,v 2.141 2007/01/09 02:14:09 tgl Exp $ -->
<!-- $PostgreSQL: pgsql/doc/src/sgml/catalogs.sgml,v 2.142 2007/01/20 23:13:01 tgl Exp $ -->
<!--
Documentation of the system catalogs, directed toward PostgreSQL developers
-->
@ -365,21 +365,10 @@
</row>
<row>
<entry><structfield>amorderstrategy</structfield></entry>
<entry><type>int2</type></entry>
<entry><structfield>amcanorder</structfield></entry>
<entry><type>bool</type></entry>
<entry></entry>
<entry>Zero if the index offers no sort order, otherwise the strategy
number of the strategy operator that describes the default
(<literal>ASC</>) sort order</entry>
</row>
<row>
<entry><structfield>amdescorder</structfield></entry>
<entry><type>int2</type></entry>
<entry></entry>
<entry>Zero if the index offers no sort order, otherwise the strategy
number of the strategy operator that describes the <literal>DESC</>
sort order</entry>
<entry>Does the access method support ordered scans?</entry>
</row>
<row>

14
doc/src/sgml/indexam.sgml
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@ -1,4 +1,4 @@
<!-- $PostgreSQL: pgsql/doc/src/sgml/indexam.sgml,v 2.19 2006/12/23 00:43:08 tgl Exp $ -->
<!-- $PostgreSQL: pgsql/doc/src/sgml/indexam.sgml,v 2.20 2007/01/20 23:13:01 tgl Exp $ -->
<chapter id="indexam">
<title>Index Access Method Interface Definition</title>
@ -442,6 +442,15 @@ amrestrpos (IndexScanDesc scan);
the scan keys to a <quote>normalized</> form.
</para>
<para>
Some access methods return index entries in a well-defined order, others
do not. If entries are returned in sorted order, the access method should
set <structname>pg_am</>.<structfield>amcanorder</> true to indicate that
it supports ordered scans.
All such access methods must use btree-compatible strategy numbers for
their equality and ordering operators.
</para>
<para>
The <function>amgettuple</> function has a <literal>direction</> argument,
which can be either <literal>ForwardScanDirection</> (the normal case)
@ -451,8 +460,7 @@ amrestrpos (IndexScanDesc scan);
the normal front-to-back direction, so <function>amgettuple</> must return
the last matching tuple in the index, rather than the first one as it
normally would. (This will only occur for access
methods that advertise they support ordered scans by setting
<structname>pg_am</>.<structfield>amorderstrategy</> nonzero.) After the
methods that advertise they support ordered scans.) After the
first call, <function>amgettuple</> must be prepared to advance the scan in
either direction from the most recently returned entry.
</para>

16
doc/src/sgml/xindex.sgml
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@ -1,4 +1,4 @@
<!-- $PostgreSQL: pgsql/doc/src/sgml/xindex.sgml,v 1.54 2007/01/09 02:14:10 tgl Exp $ -->
<!-- $PostgreSQL: pgsql/doc/src/sgml/xindex.sgml,v 1.55 2007/01/20 23:13:01 tgl Exp $ -->
<sect1 id="xindex">
<title>Interfacing Extensions To Indexes</title>
@ -287,20 +287,6 @@
return type <type>boolean</type>, since they must appear at the top
level of a <literal>WHERE</> clause to be used with an index.
</para>
<para>
By the way, the <structfield>amorderstrategy</structfield> and
<structfield>amdescorder</structfield> columns in <classname>pg_am</> tell
whether the index method supports ordered scans. Zeroes mean it doesn't;
if it does, <structfield>amorderstrategy</structfield> is the strategy
number that corresponds to the default ordering operator, and
<structfield>amdescorder</structfield> is the strategy number for the
ordering operator of an index column that has the <literal>DESC</> option.
For example, B-tree has <structfield>amorderstrategy</structfield> = 1,
which is its <quote>less than</quote> strategy number, and
<structfield>amdescorder</structfield> = 5, which is its
<quote>greater than</quote> strategy number.
</para>
</sect2>
<sect2 id="xindex-support">