[#20908] YSQL: Gate inplace index updates behind feature enablement GUC

Summary:
D36588 introduced an optimization that enabled updates to non-key columns of secondary indexes to be performed in-place (ie. not require a DELETE + INSERT).
This optimization was ON by default and was not gated behind a feature flag.

This revision introduces a Postgres GUC `yb_enable_inplace_index_update` to enable/disable the feature.
By default the GUC is set to true, keeping the optimization turned ON.
Jira: DB-9891

Test Plan:
Run the following tests:
```
./yb_build.sh --java-test 'org.yb.pgsql.TestPgRegressUpdateOptimized#schedule'
```

Reviewers: smishra, amartsinchyk, tnayak

Reviewed By: smishra

Subscribers: yql

Tags: #jenkins-ready

Differential Revision: https://phorge.dev.yugabyte.com/D38763

src/postgres/src/backend/executor/execIndexing.c

@@ -785,7 +785,8 @@ YbExecUpdateIndexTuples(ResultRelInfo *resultRelInfo,
 						ItemPointer tupleid,
 						EState *estate,
 						Bitmapset *updatedCols,
-						bool is_pk_updated)
+						bool is_pk_updated,
+						bool is_inplace_update_enabled)
 {
 	int			i;
 	int			numIndices;
@@ -882,7 +883,7 @@ YbExecUpdateIndexTuples(ResultRelInfo *resultRelInfo,
 
 			econtext->ecxt_scantuple = slot;
 			insertApplicable = ExecQual(predicate, econtext);
-			
+
 			if (deleteApplicable != insertApplicable)
 			{
 				/*
@@ -897,8 +898,7 @@ YbExecUpdateIndexTuples(ResultRelInfo *resultRelInfo,
 
 				continue;
 			}
-
-
+
 			if (!deleteApplicable)
 			{
 				/* Neither deletes nor updates applicable. Nothing to be done for this index. */
@@ -934,7 +934,8 @@ YbExecUpdateIndexTuples(ResultRelInfo *resultRelInfo,
 			}
 		}
 
-		if (!indexRelation->rd_indam->ybamcanupdatetupleinplace)
+		if (!(is_inplace_update_enabled &&
+			  indexRelation->rd_indam->ybamcanupdatetupleinplace))
 		{
 			deleteIndexes = lappend_int(deleteIndexes, i);
 			insertIndexes = lappend_int(insertIndexes, i);
@@ -987,7 +988,7 @@ YbExecUpdateIndexTuples(ResultRelInfo *resultRelInfo,
 		 *
 		 * To achieve this, we compute the list of all indexes whose key columns
 		 * are updated. These need the DELETE + INSERT. For all indexes, first
-		 * issue the deletes, followed by the inserts. 
+		 * issue the deletes, followed by the inserts.
 		 */
 
 		int j = 0;

src/postgres/src/backend/executor/nodeModifyTable.c

@@ -2456,7 +2456,7 @@ ExecUpdateEpilogue(ModifyTableContext *context, UpdateContext *updateCxt,
 			recheckIndexes =  YbExecUpdateIndexTuples(
 				resultRelInfo, slot, YBCGetYBTupleIdFromSlot(context->planSlot),
 				oldtuple, tupleid, context->estate, yb_cols_marked_for_update,
-				yb_is_pk_updated);
+				yb_is_pk_updated, mtstate->yb_is_inplace_index_update_enabled);
 		}
 	}
 	else
@@ -4564,6 +4564,8 @@ ExecInitModifyTable(ModifyTable *node, EState *estate, int eflags)
 		(node->yb_update_affected_entities != NULL &&
 		 operation == CMD_UPDATE && YbIsUpdateOptimizationEnabled());
 
+	mtstate->yb_is_inplace_index_update_enabled = yb_enable_inplace_index_update;
+
 	/* set up epqstate with dummy subplan data for the moment */
 	EvalPlanQualInit(&mtstate->mt_epqstate, estate, NULL, NIL, node->epqParam);
 	mtstate->fireBSTriggers = true;

src/postgres/src/backend/utils/misc/guc.c

@@ -2979,6 +2979,19 @@ static struct config_bool ConfigureNamesBool[] =
 		NULL, NULL, NULL
 	},
 
+	{
+		{"yb_enable_inplace_index_update", PGC_USERSET, QUERY_TUNING_OTHER,
+			gettext_noop("Enables the in-place update of non-key columns of secondary indexes "
+						 "when key columns of the index are not updated. This is useful when "
+						 "updating the included columns in a covering index among others."),
+			NULL,
+			GUC_NOT_IN_SAMPLE
+		},
+		&yb_enable_inplace_index_update,
+		true,
+		NULL, NULL, NULL
+	},
+
 	{
 		{"yb_enable_fkey_catcache", PGC_USERSET, DEVELOPER_OPTIONS,
 			gettext_noop("Enable preloading of foreign key information into the relation cache."),

src/postgres/src/backend/utils/misc/pg_yb_utils.c

@@ -1640,6 +1640,7 @@ int yb_parallel_range_size = 1024 * 1024;
 int yb_insert_on_conflict_read_batch_size = 1024;
 bool yb_enable_fkey_catcache = true;
 bool yb_enable_nop_alter_role_optimization = true;
+bool yb_enable_inplace_index_update = true;
 
 YBUpdateOptimizationOptions yb_update_optimization_options = {
 	.has_infra = true,

src/postgres/src/include/executor/executor.h

@@ -663,7 +663,8 @@ extern List *YbExecUpdateIndexTuples(ResultRelInfo *resultRelInfo,
 									 ItemPointer tupleid,
 									 EState *estate,
 									 Bitmapset *updatedCols,
-									 bool is_pk_updated);
+									 bool is_pk_updated,
+									 bool is_inplace_update_enabled);
 
 /*
  * prototypes from functions in execReplication.c

src/postgres/src/include/nodes/execnodes.h

@@ -1404,6 +1404,13 @@ typedef struct ModifyTableState
 	 * constraint checks etc. This field is set to false for single row txns.
 	 */
 	bool yb_is_update_optimization_enabled;
+
+	/*
+	 * If enabled, execution seeks to perform inplace update of non-key columns
+	 * of secondary indexes. This field is not applicable to single row txns
+	 * because they do not involve updates to secondary indexes.
+	 */
+	bool yb_is_inplace_index_update_enabled;
 } ModifyTableState;
 
 /* ----------------

src/postgres/src/include/pg_yb_utils.h

@@ -708,6 +708,12 @@ YbDdlRollbackEnabled () {
 
 extern bool yb_use_hash_splitting_by_default;
 
+/*
+ * If set to true, non-key columns of secondary indexes are updated in-place
+ * when no key columns are modified.
+ */
+extern bool yb_enable_inplace_index_update;
+
 typedef struct YBUpdateOptimizationOptions
 {
 	bool has_infra;