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Remove pg_am.amindexnulls.

Browse Source 
The only use we have had for amindexnulls is in determining whether an
index is safe to cluster on; but since the addition of the amclusterable
flag, that usage is pretty redundant.

In passing, clean up assorted sloppiness from the last patch that touched
pg_am.h: Natts_pg_am was wrong, and ambuildempty was not documented.
This commit is contained in:
Tom Lane
2011-01-08 16:08:05 -05:00
parent 56a57473a9
commit 7e2f906201
5 changed files with 35 additions and 76 deletions
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14
doc/src/sgml/catalogs.sgml
View File

@ -469,13 +469,6 @@
for the first index column?</entry>
</row>
<row>
<entry><structfield>amindexnulls</structfield></entry>
<entry><type>bool</type></entry>
<entry></entry>
<entry>Does the access method support null index entries?</entry>
</row>
<row>
<entry><structfield>amsearchnulls</structfield></entry>
<entry><type>bool</type></entry>
@ -567,6 +560,13 @@
<entry><quote>Build new index</quote> function</entry>
</row>
<row>
<entry><structfield>ambuildempty</structfield></entry>
<entry><type>regproc</type></entry>
<entry><literal><link linkend="catalog-pg-proc"><structname>pg_proc</structname></link>.oid</literal></entry>
<entry><quote>Build empty index</quote> function</entry>
</row>
<row>
<entry><structfield>ambulkdelete</structfield></entry>
<entry><type>regproc</type></entry>

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

@ -105,14 +105,15 @@
where no indexable restriction clause is given for the first index column.
When <structfield>amcanmulticol</structfield> is false,
<structfield>amoptionalkey</structfield> essentially says whether the
access method allows full-index scans without any restriction clause.
access method supports full-index scans without any restriction clause.
Access methods that support multiple index columns <emphasis>must</>
support scans that omit restrictions on any or all of the columns after
the first; however they are permitted to require some restriction to
appear for the first index column, and this is signaled by setting
<structfield>amoptionalkey</structfield> false.
<structfield>amindexnulls</structfield> asserts that index entries are
created for NULL key values. Since most indexable operators are
One reason that an index AM might set
<structfield>amoptionalkey</structfield> false is if it doesn't index
NULLs. Since most indexable operators are
strict and hence cannot return TRUE for NULL inputs,
it is at first sight attractive to not store index entries for null values:
they could never be returned by an index scan anyway. However, this
@ -129,10 +130,7 @@
used to scan for rows with <literal>a = 4</literal>, which is wrong if the
index omits rows where <literal>b</> is null.
It is, however, OK to omit rows where the first indexed column is null.
Thus, <structfield>amindexnulls</structfield> should be set true only if the
index access method indexes all rows, including arbitrary combinations of
null values. An index access method that sets
<structfield>amindexnulls</structfield> may also set
An index access method that does index nulls may also set
<structfield>amsearchnulls</structfield>, indicating that it supports
<literal>IS NULL</> and <literal>IS NOT NULL</> clauses as search
conditions.