Optimize update of tables with generated columns

When updating a table row with generated columns, only recompute those
generated columns whose base columns have changed in this update and
keep the rest unchanged.  This can result in a significant performance
benefit.  The required information was already kept in
RangeTblEntry.extraUpdatedCols; we just have to make use of it.

Reviewed-by: Pavel Stehule <pavel.stehule@gmail.com>
Discussion: https://www.postgresql.org/message-id/flat/b05e781a-fa16-6b52-6738-761181204567@2ndquadrant.com

diff --git a/src/backend/commands/copy.c b/src/backend/commands/copy.c
index 40a8ec1abd2d35a531f34e71d2d5f1c8efab9147..e79ede4cb859710b66813cb5b485693ac93ce4a0 100644 (file)
--- a/src/backend/commands/copy.c
+++ b/src/backend/commands/copy.c
@@ -3222,7 +3222,7 @@ CopyFrom(CopyState cstate)
                                /* Compute stored generated columns */
                                if (resultRelInfo->ri_RelationDesc->rd_att->constr &&
                                        resultRelInfo->ri_RelationDesc->rd_att->constr->has_generated_stored)
-                                       ExecComputeStoredGenerated(estate, myslot);
+                                       ExecComputeStoredGenerated(estate, myslot, CMD_INSERT);
 
                                /*
                                 * If the target is a plain table, check the constraints of

diff --git a/src/backend/executor/execReplication.c b/src/backend/executor/execReplication.c
index 30cba89da7ef1ff3d76bea2a783aaede78cdf06b..7194becfd99bc26047083d8f72dbf52063fe1a2d 100644 (file)
--- a/src/backend/executor/execReplication.c
+++ b/src/backend/executor/execReplication.c
@@ -419,7 +419,7 @@ ExecSimpleRelationInsert(EState *estate, TupleTableSlot *slot)
                /* Compute stored generated columns */
                if (rel->rd_att->constr &&
                        rel->rd_att->constr->has_generated_stored)
-                       ExecComputeStoredGenerated(estate, slot);
+                       ExecComputeStoredGenerated(estate, slot, CMD_INSERT);
 
                /* Check the constraints of the tuple */
                if (rel->rd_att->constr)
@@ -485,7 +485,7 @@ ExecSimpleRelationUpdate(EState *estate, EPQState *epqstate,
                /* Compute stored generated columns */
                if (rel->rd_att->constr &&
                        rel->rd_att->constr->has_generated_stored)
-                       ExecComputeStoredGenerated(estate, slot);
+                       ExecComputeStoredGenerated(estate, slot, CMD_UPDATE);
 
                /* Check the constraints of the tuple */
                if (rel->rd_att->constr)

diff --git a/src/backend/executor/nodeModifyTable.c b/src/backend/executor/nodeModifyTable.c
index 59d1a31c972dc0247a54ec160d1f446c52ecf7ea..d71c0a432207c41976244344d792308ad329c29b 100644 (file)
--- a/src/backend/executor/nodeModifyTable.c
+++ b/src/backend/executor/nodeModifyTable.c
@@ -246,7 +246,7 @@ ExecCheckTIDVisible(EState *estate,
  * Compute stored generated columns for a tuple
  */
 void
-ExecComputeStoredGenerated(EState *estate, TupleTableSlot *slot)
+ExecComputeStoredGenerated(EState *estate, TupleTableSlot *slot, CmdType cmdtype)
 {
        ResultRelInfo *resultRelInfo = estate->es_result_relation_info;
        Relation        rel = resultRelInfo->ri_RelationDesc;
@@ -269,6 +269,7 @@ ExecComputeStoredGenerated(EState *estate, TupleTableSlot *slot)
 
                resultRelInfo->ri_GeneratedExprs =
                        (ExprState **) palloc(natts * sizeof(ExprState *));
+               resultRelInfo->ri_NumGeneratedNeeded = 0;
 
                for (int i = 0; i < natts; i++)
                {
@@ -276,18 +277,41 @@ ExecComputeStoredGenerated(EState *estate, TupleTableSlot *slot)
                        {
                                Expr       *expr;
 
+                               /*
+                                * If it's an update and the current column was not marked as
+                                * being updated, then we can skip the computation.  But if
+                                * there is a BEFORE ROW UPDATE trigger, we cannot skip
+                                * because the trigger might affect additional columns.
+                                */
+                               if (cmdtype == CMD_UPDATE &&
+                                       !(rel->trigdesc && rel->trigdesc->trig_update_before_row) &&
+                                       !bms_is_member(i + 1 - FirstLowInvalidHeapAttributeNumber,
+                                                                  exec_rt_fetch(resultRelInfo->ri_RangeTableIndex, estate)->extraUpdatedCols))
+                               {
+                                       resultRelInfo->ri_GeneratedExprs[i] = NULL;
+                                       continue;
+                               }
+
                                expr = (Expr *) build_column_default(rel, i + 1);
                                if (expr == NULL)
                                        elog(ERROR, "no generation expression found for column number %d of table \"%s\"",
                                                 i + 1, RelationGetRelationName(rel));
 
                                resultRelInfo->ri_GeneratedExprs[i] = ExecPrepareExpr(expr, estate);
+                               resultRelInfo->ri_NumGeneratedNeeded++;
                        }
                }
 
                MemoryContextSwitchTo(oldContext);
        }
 
+       /*
+        * If no generated columns have been affected by this change, then skip
+        * the rest.
+        */
+       if (resultRelInfo->ri_NumGeneratedNeeded == 0)
+               return;
+
        oldContext = MemoryContextSwitchTo(GetPerTupleMemoryContext(estate));
 
        values = palloc(sizeof(*values) * natts);
@@ -300,7 +324,8 @@ ExecComputeStoredGenerated(EState *estate, TupleTableSlot *slot)
        {
                Form_pg_attribute attr = TupleDescAttr(tupdesc, i);
 
-               if (attr->attgenerated == ATTRIBUTE_GENERATED_STORED)
+               if (attr->attgenerated == ATTRIBUTE_GENERATED_STORED &&
+                       resultRelInfo->ri_GeneratedExprs[i])
                {
                        ExprContext *econtext;
                        Datum           val;
@@ -392,7 +417,7 @@ ExecInsert(ModifyTableState *mtstate,
                 */
                if (resultRelationDesc->rd_att->constr &&
                        resultRelationDesc->rd_att->constr->has_generated_stored)
-                       ExecComputeStoredGenerated(estate, slot);
+                       ExecComputeStoredGenerated(estate, slot, CMD_INSERT);
 
                /*
                 * insert into foreign table: let the FDW do it
@@ -427,7 +452,7 @@ ExecInsert(ModifyTableState *mtstate,
                 */
                if (resultRelationDesc->rd_att->constr &&
                        resultRelationDesc->rd_att->constr->has_generated_stored)
-                       ExecComputeStoredGenerated(estate, slot);
+                       ExecComputeStoredGenerated(estate, slot, CMD_INSERT);
 
                /*
                 * Check any RLS WITH CHECK policies.
@@ -1088,7 +1113,7 @@ ExecUpdate(ModifyTableState *mtstate,
                 */
                if (resultRelationDesc->rd_att->constr &&
                        resultRelationDesc->rd_att->constr->has_generated_stored)
-                       ExecComputeStoredGenerated(estate, slot);
+                       ExecComputeStoredGenerated(estate, slot, CMD_UPDATE);
 
                /*
                 * update in foreign table: let the FDW do it
@@ -1125,7 +1150,7 @@ ExecUpdate(ModifyTableState *mtstate,
                 */
                if (resultRelationDesc->rd_att->constr &&
                        resultRelationDesc->rd_att->constr->has_generated_stored)
-                       ExecComputeStoredGenerated(estate, slot);
+                       ExecComputeStoredGenerated(estate, slot, CMD_UPDATE);
 
                /*
                 * Check any RLS UPDATE WITH CHECK policies

diff --git a/src/include/executor/nodeModifyTable.h b/src/include/executor/nodeModifyTable.h
index 0495cae051c79eca103152f613b97830c73225a1..4ec4ebdabc13e81cac9fb3d04e313fc0a89a2247 100644 (file)
--- a/src/include/executor/nodeModifyTable.h
+++ b/src/include/executor/nodeModifyTable.h
@@ -15,7 +15,7 @@
 
 #include "nodes/execnodes.h"
 
-extern void ExecComputeStoredGenerated(EState *estate, TupleTableSlot *slot);
+extern void ExecComputeStoredGenerated(EState *estate, TupleTableSlot *slot, CmdType cmdtype);
 
 extern ModifyTableState *ExecInitModifyTable(ModifyTable *node, EState *estate, int eflags);
 extern void ExecEndModifyTable(ModifyTableState *node);

diff --git a/src/include/nodes/execnodes.h b/src/include/nodes/execnodes.h
index 5d5b38b8799a635e9dc3a31bbeeb58edf12ba93b..cd3ddf781f1e58ae8f38d5139b269e25ac5e88c1 100644 (file)
--- a/src/include/nodes/execnodes.h
+++ b/src/include/nodes/execnodes.h
@@ -457,6 +457,9 @@ typedef struct ResultRelInfo
        /* array of stored generated columns expr states */
        ExprState **ri_GeneratedExprs;
 
+       /* number of stored generated columns we need to compute */
+       int                     ri_NumGeneratedNeeded;
+
        /* for removing junk attributes from tuples */
        JunkFilter *ri_junkFilter;