Ensure we allocate NAMEDATALEN bytes for names in Index Only Scans

As an optimization, we store "name" columns as cstrings in btree
indexes.

Here we modify it so that Index Only Scans convert these cstrings back
to names with NAMEDATALEN bytes rather than storing the cstring in the
tuple slot, as was happening previously.

Bug: #17855
Reported-by: Alexander Lakhin
Reviewed-by: Alexander Lakhin, Tom Lane
Discussion: https://postgr.es/m/17855-5f523e0f9769a566@postgresql.org
Backpatch-through: 12, all supported versions

diff --git a/src/backend/executor/nodeIndexonlyscan.c b/src/backend/executor/nodeIndexonlyscan.c
index fcf6d1d932184a36661590a4961600f5aba084e1..b49194c0167afd2901bae933f6d163a7adc33bd5 100644 (file)
--- a/src/backend/executor/nodeIndexonlyscan.c
+++ b/src/backend/executor/nodeIndexonlyscan.c
@@ -35,18 +35,20 @@
 #include "access/tableam.h"
 #include "access/tupdesc.h"
 #include "access/visibilitymap.h"
+#include "catalog/pg_type.h"
 #include "executor/executor.h"
 #include "executor/nodeIndexonlyscan.h"
 #include "executor/nodeIndexscan.h"
 #include "miscadmin.h"
 #include "storage/bufmgr.h"
 #include "storage/predicate.h"
+#include "utils/builtins.h"
 #include "utils/rel.h"
 
 
 static TupleTableSlot *IndexOnlyNext(IndexOnlyScanState *node);
-static void StoreIndexTuple(TupleTableSlot *slot, IndexTuple itup,
-                           TupleDesc itupdesc);
+static void StoreIndexTuple(IndexOnlyScanState *node, TupleTableSlot *slot,
+                           IndexTuple itup, TupleDesc itupdesc);
 
 
 /* ----------------------------------------------------------------
@@ -205,7 +207,7 @@ IndexOnlyNext(IndexOnlyScanState *node)
            ExecForceStoreHeapTuple(scandesc->xs_hitup, slot, false);
        }
        else if (scandesc->xs_itup)
-           StoreIndexTuple(slot, scandesc->xs_itup, scandesc->xs_itupdesc);
+           StoreIndexTuple(node, slot, scandesc->xs_itup, scandesc->xs_itupdesc);
        else
            elog(ERROR, "no data returned for index-only scan");
 
@@ -263,7 +265,8 @@ IndexOnlyNext(IndexOnlyScanState *node)
  * right now we don't need it elsewhere.
  */
 static void
-StoreIndexTuple(TupleTableSlot *slot, IndexTuple itup, TupleDesc itupdesc)
+StoreIndexTuple(IndexOnlyScanState *node, TupleTableSlot *slot,
+               IndexTuple itup, TupleDesc itupdesc)
 {
    /*
     * Note: we must use the tupdesc supplied by the AM in index_deform_tuple,
@@ -276,6 +279,37 @@ StoreIndexTuple(TupleTableSlot *slot, IndexTuple itup, TupleDesc itupdesc)
 
    ExecClearTuple(slot);
    index_deform_tuple(itup, itupdesc, slot->tts_values, slot->tts_isnull);
+
+   /*
+    * Copy all name columns stored as cstrings back into a NAMEDATALEN byte
+    * sized allocation.  We mark this branch as unlikely as generally "name"
+    * is used only for the system catalogs and this would have to be a user
+    * query running on those or some other user table with an index on a name
+    * column.
+    */
+   if (unlikely(node->ioss_NameCStringAttNums != NULL))
+   {
+       int         attcount = node->ioss_NameCStringCount;
+
+       for (int idx = 0; idx < attcount; idx++)
+       {
+           int         attnum = node->ioss_NameCStringAttNums[idx];
+           Name        name;
+
+           /* skip null Datums */
+           if (slot->tts_isnull[attnum])
+               continue;
+
+           /* allocate the NAMEDATALEN and copy the datum into that memory */
+           name = (Name) MemoryContextAlloc(node->ss.ps.ps_ExprContext->ecxt_per_tuple_memory,
+                                            NAMEDATALEN);
+
+           /* use namestrcpy to zero-pad all trailing bytes */
+           namestrcpy(name, DatumGetCString(slot->tts_values[attnum]));
+           slot->tts_values[attnum] = NameGetDatum(name);
+       }
+   }
+
    ExecStoreVirtualTuple(slot);
 }
 
@@ -473,8 +507,11 @@ ExecInitIndexOnlyScan(IndexOnlyScan *node, EState *estate, int eflags)
 {
    IndexOnlyScanState *indexstate;
    Relation    currentRelation;
+   Relation    indexRelation;
    LOCKMODE    lockmode;
    TupleDesc   tupDesc;
+   int         indnkeyatts;
+   int         namecount;
 
    /*
     * create state structure
@@ -547,7 +584,8 @@ ExecInitIndexOnlyScan(IndexOnlyScan *node, EState *estate, int eflags)
 
    /* Open the index relation. */
    lockmode = exec_rt_fetch(node->scan.scanrelid, estate)->rellockmode;
-   indexstate->ioss_RelationDesc = index_open(node->indexid, lockmode);
+   indexRelation = index_open(node->indexid, lockmode);
+   indexstate->ioss_RelationDesc = indexRelation;
 
    /*
     * Initialize index-specific scan state
@@ -560,7 +598,7 @@ ExecInitIndexOnlyScan(IndexOnlyScan *node, EState *estate, int eflags)
     * build the index scan keys from the index qualification
     */
    ExecIndexBuildScanKeys((PlanState *) indexstate,
-                          indexstate->ioss_RelationDesc,
+                          indexRelation,
                           node->indexqual,
                           false,
                           &indexstate->ioss_ScanKeys,
@@ -574,7 +612,7 @@ ExecInitIndexOnlyScan(IndexOnlyScan *node, EState *estate, int eflags)
     * any ORDER BY exprs have to be turned into scankeys in the same way
     */
    ExecIndexBuildScanKeys((PlanState *) indexstate,
-                          indexstate->ioss_RelationDesc,
+                          indexRelation,
                           node->indexorderby,
                           true,
                           &indexstate->ioss_OrderByKeys,
@@ -603,6 +641,49 @@ ExecInitIndexOnlyScan(IndexOnlyScan *node, EState *estate, int eflags)
        indexstate->ioss_RuntimeContext = NULL;
    }
 
+   indexstate->ioss_NameCStringAttNums = NULL;
+   indnkeyatts = indexRelation->rd_index->indnkeyatts;
+   namecount = 0;
+
+   /*
+    * The "name" type for btree uses text_ops which results in storing
+    * cstrings in the indexed keys rather than names.  Here we detect that in
+    * a generic way in case other index AMs want to do the same optimization.
+    * Check for opclasses with an opcintype of NAMEOID and an index tuple
+    * descriptor with CSTRINGOID.  If any of these are found, create an array
+    * marking the index attribute number of each of them.  StoreIndexTuple()
+    * handles copying the name Datums into a NAMEDATALEN-byte allocation.
+    */
+
+   /* First, count the number of such index keys */
+   for (int attnum = 0; attnum < indnkeyatts; attnum++)
+   {
+       if (indexRelation->rd_att->attrs[attnum].atttypid == CSTRINGOID &&
+           indexRelation->rd_opcintype[attnum] == NAMEOID)
+           namecount++;
+   }
+
+   if (namecount > 0)
+   {
+       int         idx = 0;
+
+       /*
+        * Now create an array to mark the attribute numbers of the keys that
+        * need to be converted from cstring to name.
+        */
+       indexstate->ioss_NameCStringAttNums = (AttrNumber *)
+           palloc(sizeof(AttrNumber) * namecount);
+
+       for (int attnum = 0; attnum < indnkeyatts; attnum++)
+       {
+           if (indexRelation->rd_att->attrs[attnum].atttypid == CSTRINGOID &&
+               indexRelation->rd_opcintype[attnum] == NAMEOID)
+               indexstate->ioss_NameCStringAttNums[idx++] = (AttrNumber) attnum;
+       }
+   }
+
+   indexstate->ioss_NameCStringCount = namecount;
+
    /*
     * all done.
     */

diff --git a/src/include/catalog/pg_opclass.dat b/src/include/catalog/pg_opclass.dat
index 6c30770fe7c8651f1595c97f448f3603c5eeff1f..f503c652ebca64a4db641bf58b991ff873d5aee1 100644 (file)
--- a/src/include/catalog/pg_opclass.dat
+++ b/src/include/catalog/pg_opclass.dat
@@ -91,8 +91,11 @@
 # Here's an ugly little hack to save space in the system catalog indexes.
 # btree doesn't ordinarily allow a storage type different from input type;
 # but cstring and name are the same thing except for trailing padding,
-# and we can safely omit that within an index entry.  So we declare the
-# btree opclass for name as using cstring storage type.
+# so we choose to omit that within an index entry.  Here we declare the
+# btree opclass for name as using cstring storage type.  This does require
+# that we pad the cstring out with the full NAMEDATALEN bytes when performing
+# index-only scans.  See corresponding hacks in ExecInitIndexOnlyScan() and
+# StoreIndexTuple().
 { opcmethod => 'btree', opcname => 'name_ops', opcfamily => 'btree/text_ops',
   opcintype => 'name', opckeytype => 'cstring' },
 

diff --git a/src/include/nodes/execnodes.h b/src/include/nodes/execnodes.h
index d927ac44a82bca1d46bb8877c8c422ce71d28d9b..8bc421e7c0508b0374ae04ea6e2004408e2dd727 100644 (file)
--- a/src/include/nodes/execnodes.h
+++ b/src/include/nodes/execnodes.h
@@ -1690,6 +1690,8 @@ typedef struct IndexScanState
  *     TableSlot          slot for holding tuples fetched from the table
  *     VMBuffer           buffer in use for visibility map testing, if any
  *     PscanLen           size of parallel index-only scan descriptor
+ *     NameCStringAttNums attnums of name typed columns to pad to NAMEDATALEN
+ *     NameCStringCount   number of elements in the NameCStringAttNums array
  * ----------------
  */
 typedef struct IndexOnlyScanState
@@ -1709,6 +1711,8 @@ typedef struct IndexOnlyScanState
    TupleTableSlot *ioss_TableSlot;
    Buffer      ioss_VMBuffer;
    Size        ioss_PscanLen;
+   AttrNumber *ioss_NameCStringAttNums;
+   int         ioss_NameCStringCount;
 } IndexOnlyScanState;
 
 /* ----------------

diff --git a/src/test/regress/expected/index_including.out b/src/test/regress/expected/index_including.out
index 86510687c743f54fd49f508d09176f10a8c52cd3..ea8b2454bf8cd45951d53a05bfef3612099e398d 100644 (file)
--- a/src/test/regress/expected/index_including.out
+++ b/src/test/regress/expected/index_including.out
@@ -398,3 +398,28 @@ Indexes:
     "tbl_c1_c2_c3_c4_key" UNIQUE CONSTRAINT, btree (c1, c2) INCLUDE (c3, c4)
 
 DROP TABLE tbl;
+/*
+ * 10. Test coverage for names stored as cstrings in indexes
+ */
+CREATE TABLE nametbl (c1 int, c2 name, c3 float);
+CREATE INDEX nametbl_c1_c2_idx ON nametbl (c2, c1) INCLUDE (c3);
+INSERT INTO nametbl VALUES(1, 'two', 3.0);
+VACUUM nametbl;
+SET enable_seqscan = 0;
+-- Ensure we get an index only scan plan
+EXPLAIN (COSTS OFF) SELECT c2, c1, c3 FROM nametbl WHERE c2 = 'two' AND c1 = 1;
+                     QUERY PLAN                     
+----------------------------------------------------
+ Index Only Scan using nametbl_c1_c2_idx on nametbl
+   Index Cond: ((c2 = 'two'::name) AND (c1 = 1))
+(2 rows)
+
+-- Validate the results look sane
+SELECT c2, c1, c3 FROM nametbl WHERE c2 = 'two' AND c1 = 1;
+ c2  | c1 | c3 
+-----+----+----
+ two |  1 |  3
+(1 row)
+
+RESET enable_seqscan;
+DROP TABLE nametbl;

diff --git a/src/test/regress/sql/index_including.sql b/src/test/regress/sql/index_including.sql
index 44b340053b75b2b2bdc500bd0a9472d368d1ab7b..ad9cbdd02807bc580f9b6584eda6d674f8fc93ef 100644 (file)
--- a/src/test/regress/sql/index_including.sql
+++ b/src/test/regress/sql/index_including.sql
@@ -217,3 +217,22 @@ ALTER TABLE tbl ALTER c1 TYPE bigint;
 ALTER TABLE tbl ALTER c3 TYPE bigint;
 \d tbl
 DROP TABLE tbl;
+
+/*
+ * 10. Test coverage for names stored as cstrings in indexes
+ */
+CREATE TABLE nametbl (c1 int, c2 name, c3 float);
+CREATE INDEX nametbl_c1_c2_idx ON nametbl (c2, c1) INCLUDE (c3);
+INSERT INTO nametbl VALUES(1, 'two', 3.0);
+VACUUM nametbl;
+SET enable_seqscan = 0;
+
+-- Ensure we get an index only scan plan
+EXPLAIN (COSTS OFF) SELECT c2, c1, c3 FROM nametbl WHERE c2 = 'two' AND c1 = 1;
+
+-- Validate the results look sane
+SELECT c2, c1, c3 FROM nametbl WHERE c2 = 'two' AND c1 = 1;
+
+RESET enable_seqscan;
+
+DROP TABLE nametbl;
\ No newline at end of file