8000 Replace simple constant pg_am.amcanreturn with an AM support function. · postgrespro/postgres_cluster@3695a55 · GitHub
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Replace simple constant pg_am.amcanreturn with an AM support function.
The need for this was debated when we put in the index-only-scan feature, but at the time we had no near-term expectation of having AMs that could support such scans for only some indexes; so we kept it simple. However, the SP-GiST AM forces the issue, so let's fix it. This patch only installs the new API; no behavior actually changes.
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15 files changed

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-46
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  • pg_proc.h
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  • utils

    • 15 files changed

    +103
    -46
    lines changed

    ‎doc/src/sgml/catalogs.sgml‎

    Lines changed: 8 additions & 7 deletions
    Original file line numberDiff line numberDiff line change
    @@ -481,13 +481,6 @@
    481481
    <entry>Does the access method support multicolumn indexes?</entry>
    482482
    </row>
    483483

    484-
    <row>
    485-
    <entry><structfield>amcanreturn</structfield></entry>
    486-
    <entry><type>bool</type></entry>
    487-
    <entry></entry>
    488-
    <entry>Can the access method return the contents of index entries?</entry>
    489-
    </row>
    490-
    491484
    <row>
    492485
    <entry><structfield>amoptionalkey</structfield></entry>
    493486
    <entry><type>bool</type></entry>
    @@ -622,6 +615,14 @@
    622615
    <entry>Post-<command>VACUUM</command> cleanup function</entry>
    623616
    </row>
    624617

    618+
    <row>
    619+
    <entry><structfield>amcanreturn</structfield></entry>
    620+
    <entry><type>regproc</type></entry>
    621+
    <entry><literal><link linkend="catalog-pg-proc"><structname>pg_proc</structname></link>.oid</literal></entry>
    622+
    <entry>Function to check whether index supports index-only scans,
    623+
    or zero if none</entry>
    624+
    </row>
    625+
    625626
    <row>
    626627
    <entry><structfield>amcostestimate</structfield></entry>
    627628
    <entry><type>regproc</type></entry>

    ‎doc/src/sgml/indexam.sgml‎

    Lines changed: 16 additions & 8 deletions
    Original file line numberDiff line numberDiff line change
    @@ -134,11 +134,6 @@
    134134
    <structfield>amsearchnulls</structfield>, indicating that it supports
    135135
    <literal>IS NULL</> and <literal>IS NOT NULL</> clauses as search
    136136
    conditions.
    137-
    An index method can also set <structfield>amcanreturn</structfield>,
    138-
    indicating that it can support <firstterm>index-only scans</> by returning
    139-
    the indexed column values for an index entry in the form of an IndexTuple.
    140-
    (An example of an index AM that cannot do this is hash, which stores only
    141-
    the hash values not the original data.)
    142137
    </para>
    143138

    144139
    </sect1>
    @@ -278,6 +273,19 @@ amvacuumcleanup (IndexVacuumInfo *info,
    278273

    279274
    <para>
    280275
    <programlisting>
    276+
    bool
    277+
    amcanreturn (Relation indexRelation);
    278+
    </programlisting>
    279+
    Check whether the index can support <firstterm>index-only scans</> by
    280+
    returning the indexed column values for an index entry in the form of an
    281+
    IndexTuple. Return TRUE if so, else FALSE. If the index AM can never
    282+
    support index-only scans (an example is hash, which stores only
    283+
    the hash values not the original data), it is sufficient to set its
    284+
    <structfield>amcanreturn</> field to zero in <structname>pg_am</>.
    285+
    </para>
    286+
    287+
    <para>
    288+
    <programlisting>
    281289
    void
    282290
    amcostestimate (PlannerInfo *root,
    283291
    IndexOptInfo *index,
    @@ -391,9 +399,9 @@ amgettuple (IndexScanDesc scan,
    391399
    </para>
    392400

    393401
    <para>
    394-
    If the access method supports index-only scans (i.e.,
    395-
    <structfield>amcanreturn</structfield> is TRUE in its <structname>pg_am</>
    396-
    row), then on success it must also check
    402+
    If the index supports index-only scans (i.e.,
    403+
    <function>amcanreturn</function> returns TRUE for it),
    404+
    then on success the AM must also check
    397405
    <literal>scan-&gt;xs_want_itup</>, and if that is true it must return
    398406
    the original indexed data for the index entry, in the form of an
    399407
    <structname>IndexTuple</> pointer stored at <literal>scan-&gt;xs_itup</>,

    ‎src/backend/access/index/indexam.c‎

    Lines changed: 22 additions & 0 deletions
    Original file line numberDiff line numberDiff line change
    @@ -26,6 +26,7 @@
    2626
    * index_getbitmap - get all tuples from a scan
    2727
    * index_bulk_delete - bulk deletion of index tuples
    2828
    * index_vacuum_cleanup - post-deletion cleanup of an index
    29+
    * index_can_return - does index support index-only scans?
    2930
    * index_getprocid - get a support procedure OID
    3031
    * index_getprocinfo - get a support procedure's lookup info
    3132
    *
    @@ -711,6 +712,27 @@ index_vacuum_cleanup(IndexVacuumInfo *info,
    711712
    return result;
    712713
    }
    713714

    715+
    /* ----------------
    716+
    * index_can_return - does index support index-only scans?
    717+
    * ----------------
    718+
    */
    719+
    bool
    720+
    index_can_return(Relation indexRelation)
    721+
    {
    722+
    FmgrInfo *procedure;
    723+
    724+
    RELATION_CHECKS;
    725+
    726+
    /* amcanreturn is optional; assume FALSE if not provided by AM */
    727+
    if (!RegProcedureIsValid(indexRelation->rd_am->amcanreturn))
    728+
    return false;
    729+
    730+
    GET_REL_PROCEDURE(amcanreturn);
    731+
    732+
    return DatumGetBool(FunctionCall1(procedure,
    733+
    PointerGetDatum(indexRelation)));
    734+
    }
    735+
    714736
    /* ----------------
    715737
    * index_getprocid
    716738
    *

    ‎src/backend/access/nbtree/nbtree.c‎

    Lines changed: 11 additions & 0 deletions
    Original file line numberDiff line numberDiff line change
    @@ -1091,3 +1091,14 @@ btvacuumpage(BTVacState *vstate, BlockNumber blkno, BlockNumber orig_blkno)
    10911091
    goto restart;
    10921092
    }
    10931093
    }
    1094+
    1095+
    /*
    1096+
    * btcanreturn() -- Check whether btree indexes support index-only scans.
    1097+
    *
    1098+
    * btrees always do, so this is trivial.
    1099+
    */
    1100+
    Datum
    1101+
    btcanreturn(PG_FUNCTION_ARGS)
    1102+
    {
    1103+
    PG_RETURN_BOOL(true);
    1104+
    }

    ‎src/backend/access/spgist/spgscan.c‎

    Lines changed: 7 additions & 0 deletions
    Original file line numberDiff line numberDiff line change
    @@ -559,3 +559,10 @@ spggettuple(PG_FUNCTION_ARGS)
    559559

    560560
    PG_RETURN_BOOL(false);
    561561
    }
    562+
    563+
    Datum
    564+
    spgcanreturn(PG_FUNCTION_ARGS)
    565+
    {
    566+
    /* Not implemented yet */
    567+
    PG_RETURN_BOOL(false);
    568+
    }

    ‎src/backend/optimizer/path/indxpath.c‎

    Lines changed: 2 additions & 2 deletions
    Original file line numberDiff line numberDiff line change
    @@ -1075,10 +1075,10 @@ check_index_only(RelOptInfo *rel, IndexOptInfo *index)
    10751075
    ListCell *lc;
    10761076
    int i;
    10771077

    1078-
    /* Index-only scans must be enabled, and AM must be capable of it */
    1078+
    /* Index-only scans must be enabled, and index must be capable of them */
    10791079
    if (!enable_indexonlyscan)
    10801080
    return false;
    1081-
    if (!index->amcanreturn)
    1081+
    if (!index->canreturn)
    10821082
    return false;
    10831083

    10841084
    /*

    ‎src/backend/optimizer/util/plancat.c‎

    Lines changed: 1 addition & 1 deletion
    Original file line numberDiff line numberDiff line change
    @@ -212,8 +212,8 @@ get_relation_info(PlannerInfo *root, Oid relationObjectId, bool inhparent,
    212212

    213213
    info->relam = indexRelation->rd_rel->relam;
    214214
    info->amcostestimate = indexRelation->rd_am->amcostestimate;
    215+
    info->canreturn = index_can_return(indexRelation);
    215216
    info->amcanorderbyop = indexRelation->rd_am->amcanorderbyop;
    216-
    info->amcanreturn = indexRelation->rd_am->amcanreturn;
    217217
    info->amoptionalkey = indexRelation->rd_am->amoptionalkey;
    218218
    info->amsearcharray = indexRelation->rd_am->amsearcharray;
    219219
    info->amsearchnulls = indexRelation->rd_am->amsearchnulls;

    ‎src/include/access/genam.h‎

    Lines changed: 1 addition & 0 deletions
    Original file line numberDiff line numberDiff line change
    @@ -156,6 +156,7 @@ extern IndexBulkDeleteResult *index_bulk_delete(IndexVacuumInfo *info,
    156156
    void *callback_state);
    157157
    extern IndexBulkDeleteResult *index_vacuum_cleanup(IndexVacuumInfo *info,
    158158
    IndexBulkDeleteResult *stats);
    159+
    extern bool index_can_return(Relation indexRelation);
    159160
    extern RegProcedure index_getprocid(Relation irel, AttrNumber attnum,
    160161
    uint16 procnum);
    161162
    extern FmgrInfo *index_getprocinfo(Relation irel, AttrNumber attnum,

    ‎src/include/access/nbtree.h‎

    Lines changed: 1 addition & 0 deletions
    Original file line numberDiff line numberDiff line change
    @@ -607,6 +607,7 @@ extern Datum btmarkpos(PG_FUNCTION_ARGS);
    607607
    extern Datum btrestrpos(PG_FUNCTION_ARGS);
    608608
    extern Datum btbulkdelete(PG_FUNCTION_ARGS);
    609609
    extern Datum btvacuumcleanup(PG_FUNCTION_ARGS);
    610+
    extern Datum btcanreturn(PG_FUNCTION_ARGS);
    610611
    extern Datum btoptions(PG_FUNCTION_ARGS);
    611612

    612613
    /*

    ‎src/include/access/spgist.h‎

    Lines changed: 1 addition & 0 deletions
    Original file line numberDiff line numberDiff line change
    @@ -182,6 +182,7 @@ extern Datum spgmarkpos(PG_FUNCTION_ARGS);
    182182
    extern Datum spgrestrpos(PG_FUNCTION_ARGS);
    183183
    extern Datum spggetbitmap(PG_FUNCTION_ARGS);
    184184
    extern Datum spggettuple(PG_FUNCTION_ARGS);
    185+
    extern Datum spgcanreturn(PG_FUNCTION_ARGS);
    185186

    186187
    /* spgutils.c */
    187188
    extern Datum spgoptions(PG_FUNCTION_ARGS);

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