REPACK CONCURRENTLY: Initialize the range table more honestly

We were skipping a bunch of things that are mostly unnecessary for
REPACK.  However, one thing that seems would be better to pass closer to
truth, is the updatedCols bitmapset in the range table entry for the
repacked table.  Cons up an RTE and install it into the EState.

This only has an effect on btree indexes, because certain operations are
optimized in the case of unchanged columns; and even then, correctnesss
is not being compromised.

The values we pass after this commit are not fully trustworthy either,
because we simply say "all columns were updated" for all insert/updates,
regardless of whether their values were actually modified or not.
However, this way we err to the side of caution rather than to the
opposite direction as we were originally doing.  This could be refined
in the future, but there's a trade-off: determining whether the column
was in fact updated could be expensive.

Author: Antonin Houska <ah@cybertec.at>
Reviewed-by: Ewan Young <kdbase.hack@gmail.com>
Backpatch-through: 19
Discussion: https://postgr.es/m/18222.1782126731@localhost

diff --git a/src/backend/commands/repack.c b/src/backend/commands/repack.c
index 83a49afe7e1a8bc83022f168621a5691d1039975..faa07d1a118b049e66299eeaa199b495f5b451da 100644 (file)
--- a/src/backend/commands/repack.c
+++ b/src/backend/commands/repack.c
@@ -63,6 +63,7 @@
 #include "libpq/pqmq.h"
 #include "miscadmin.h"
 #include "optimizer/optimizer.h"
+#include "parser/parse_relation.h"
 #include "pgstat.h"
 #include "replication/logicalrelation.h"
 #include "storage/bufmgr.h"
@@ -3019,8 +3020,60 @@ initialize_change_context(ChangeContext *chgcxt,
        /* Only initialize fields needed by ExecInsertIndexTuples(). */
        chgcxt->cc_estate = CreateExecutorState();
 
-       chgcxt->cc_rri = (ResultRelInfo *) palloc(sizeof(ResultRelInfo));
-       InitResultRelInfo(chgcxt->cc_rri, relation, 0, 0, 0);
+       /*
+        * Set up a range table for the executor, containing our repacked table as
+        * its only member.
+        */
+       {
+               RangeTblEntry *rte;
+               TupleDesc       desc = RelationGetDescr(relation);
+               List       *perminfos = NIL;
+               Bitmapset  *updatedCols = NULL;
+               RTEPermissionInfo *perminfo;
+
+               /*
+                * For our use, the RTE only needs to have perminfoindex initialized,
+                * but there's no reason to not set the fields whose values we have at
+                * hand.
+                */
+               rte = makeNode(RangeTblEntry);
+               rte->rtekind = RTE_RELATION;
+               rte->relid = RelationGetRelid(relation);
+               rte->relkind = RelationGetForm(relation)->relkind;
+               /* Create the RTEPermissionInfo instance (and set ->perminfoindex). */
+               addRTEPermissionInfo(&perminfos, rte);
+
+               /*
+                * Initialize updatedCols to show that all columns are updated.  This
+                * is of course not necessarily true, and we cannot know this early;
+                * but this is only used by ExecInsertIndexTuples to flag index
+                * updates with no logical value changes, so if it's wrong, nothing
+                * terribly bad happens. We may want to improve this someday though.
+                *
+                * Don't claim that dropped columns are changed though.
+                */
+               for (int i = 0; i < desc->natts; i++)
+               {
+                       CompactAttribute *attr = TupleDescCompactAttr(desc, i);
+
+                       if (attr->attisdropped)
+                               continue;
+                       updatedCols = bms_add_member(updatedCols,
+                                                                                i + 1 - FirstLowInvalidHeapAttributeNumber);
+               }
+
+               /* install updatedCols in the right place */
+               perminfo = getRTEPermissionInfo(perminfos, rte);
+               perminfo->updatedCols = updatedCols;
+
+               /* finally we can initialize the range table proper */
+               ExecInitRangeTable(chgcxt->cc_estate, list_make1(rte), perminfos,
+                                                  bms_make_singleton(1));
+       }
+
+       /* Set up our ResultRelInfo to use for index updates */
+       chgcxt->cc_rri = makeNode(ResultRelInfo);
+       InitResultRelInfo(chgcxt->cc_rri, relation, 1, NULL, 0);
        ExecOpenIndices(chgcxt->cc_rri, false);
 
        /*