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Teach SP-GiST to do index-only scans.

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Operator classes can specify whether or not they support this; this
preserves the flexibility to use lossy representations within an index.

In passing, move constant data about a given index into the rd_amcache
cache area, instead of doing fresh lookups each time we start an index
operation.  This is mainly to try to make sure that spgcanreturn() has
insignificant cost; I still don't have any proof that it matters for
actual index accesses.  Also, get rid of useless copying of FmgrInfo
pointers; we can perfectly well use the relcache's versions in-place.
This commit is contained in:
Tom Lane
2011-12-19 14:58:41 -05:00
parent 3695a55513
commit 9220362493
10 changed files with 286 additions and 172 deletions
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15
doc/src/sgml/spgist.sgml
View File

@ -145,6 +145,7 @@ typedef struct spgConfigOut
{
Oid prefixType; /* Data type of inner-tuple prefixes */
Oid labelType; /* Data type of inner-tuple node labels */
bool canReturnData; /* Opclass can reconstruct original data */
bool longValuesOK; /* Opclass can cope with values > 1 page */
} spgConfigOut;
</programlisting>
@ -159,6 +160,8 @@ typedef struct spgConfigOut
<structfield>prefixType</> can be set to <literal>VOIDOID</>.
Likewise, for operator classes that do not use node labels,
<structfield>labelType</> can be set to <literal>VOIDOID</>.
<structfield>canReturnData</> should be set true if the operator class
is capable of reconstructing the originally-supplied index value.
<structfield>longValuesOK</> should be set true only when the
<structfield>attType</> is of variable length and the operator
class is capable of segmenting long values by repeated suffixing
@ -441,6 +444,7 @@ typedef struct spgInnerConsistentIn
Datum reconstructedValue; /* value reconstructed at parent */
int level; /* current level (counting from zero) */
bool returnData; /* original data must be returned? */
/* Data from current inner tuple */
bool allTheSame; /* tuple is marked all-the-same? */
@ -467,6 +471,9 @@ typedef struct spgInnerConsistentOut
parent level.
<structfield>level</> is the current inner tuple's level, starting at
zero for the root level.
<structfield>returnData</> is <literal>true</> if reconstructed data is
required for this query; this will only be so if the
<function>config</> function asserted <structfield>canReturnData</>.
<structfield>allTheSame</> is true if the current inner tuple is
marked <quote>all-the-same</>; in this case all the nodes have the
same label (if any) and so either all or none of them match the query
@ -525,12 +532,14 @@ typedef struct spgLeafConsistentIn
Datum reconstructedValue; /* value reconstructed at parent */
int level; /* current level (counting from zero) */
bool returnData; /* original data must be returned? */
Datum leafDatum; /* datum in leaf tuple */
} spgLeafConsistentIn;
typedef struct spgLeafConsistentOut
{
Datum leafValue; /* reconstructed original data, if any */
bool recheck; /* set true if operator must be rechecked */
} spgLeafConsistentOut;
</programlisting>
@ -543,6 +552,9 @@ typedef struct spgLeafConsistentOut
parent level.
<structfield>level</> is the current leaf tuple's level, starting at
zero for the root level.
<structfield>returnData</> is <literal>true</> if reconstructed data is
required for this query; this will only be so if the
<function>config</> function asserted <structfield>canReturnData</>.
<structfield>leafDatum</> is the key value stored in the current
leaf tuple.
</para>
@ -550,6 +562,9 @@ typedef struct spgLeafConsistentOut
<para>
The function must return <literal>true</> if the leaf tuple matches the
query, or <literal>false</> if not. In the <literal>true</> case,
if <structfield>returnData</> is <literal>true</> then
<structfield>leafValue</> must be set to the value originally supplied
to be indexed for this leaf tuple. Also,
<structfield>recheck</> may be set to <literal>true</> if the match
is uncertain and so the operator must be re-applied to the actual heap
tuple to verify the match.