Store ShardInterval instead of shardId in RangeTableFragments.

For CITUS_RTE_RELATION type fragments, reloading shardIntervals from the
database is rather expensive. So store a pointer to the full shard
interval, instead of just the shard id.  There's no new memory lifetime
hazards here, because we already passed a pointer to the shardInterval's
->shardId field around.

The plan time for the query in issue #607 goes from 2889 ms to 106 ms.
with this change.

src/backend/distributed/planner/multi_physical_planner.c

@@ -2008,7 +2008,7 @@ SubquerySqlTaskList(Job *job)
 			ShardInterval *shardInterval = (ShardInterval *) lfirst(shardIntervalCell);
 
 			RangeTableFragment *shardFragment = palloc0(fragmentSize);
-			shardFragment->fragmentReference = &(shardInterval->shardId);
+			shardFragment->fragmentReference = shardInterval;
 			shardFragment->fragmentType = CITUS_RTE_RELATION;
 			shardFragment->rangeTableId = tableId;
 
@@ -2449,7 +2449,7 @@ RangeTableFragmentsList(List *rangeTableList, List *whereClauseList,
 					(ShardInterval *) lfirst(shardIntervalCell);
 
 				RangeTableFragment *shardFragment = palloc0(fragmentSize);
-				shardFragment->fragmentReference = &shardInterval->shardId;
+				shardFragment->fragmentReference = shardInterval;
 				shardFragment->fragmentType = CITUS_RTE_RELATION;
 				shardFragment->rangeTableId = tableId;
 
@@ -3582,14 +3582,16 @@ FragmentInterval(RangeTableFragment *fragment)
 	ShardInterval *fragmentInterval = NULL;
 	if (fragment->fragmentType == CITUS_RTE_RELATION)
 	{
-		uint64 *shardId = (uint64 *) fragment->fragmentReference;
+		Assert(CitusIsA(fragment->fragmentReference, ShardInterval));
-
+		fragmentInterval = (ShardInterval *) fragment->fragmentReference;
-		fragmentInterval = LoadShardInterval(*shardId);
 	}
 	else if (fragment->fragmentType == CITUS_RTE_REMOTE_QUERY)
 	{
-		Task *mergeTask = (Task *) fragment->fragmentReference;
+		Task *mergeTask = NULL;
 
+		Assert(CitusIsA(fragment->fragmentReference, Task));
+
+		mergeTask = (Task *) fragment->fragmentReference;
 		fragmentInterval = mergeTask->shardInterval;
 	}
 
@@ -3687,22 +3689,24 @@ UniqueFragmentList(List *fragmentList)
 
 	foreach(fragmentCell, fragmentList)
 	{
-		uint64 *shardId = NULL;
+		ShardInterval *shardInterval = NULL;
 		bool shardIdAlreadyAdded = false;
 		ListCell *uniqueFragmentCell = NULL;
 
 		RangeTableFragment *fragment = (RangeTableFragment *) lfirst(fragmentCell);
 		Assert(fragment->fragmentType == CITUS_RTE_RELATION);
 
-		shardId = fragment->fragmentReference;
+		Assert(CitusIsA(fragment->fragmentReference, ShardInterval));
+		shardInterval = (ShardInterval *) fragment->fragmentReference;
 
 		foreach(uniqueFragmentCell, uniqueFragmentList)
 		{
 			RangeTableFragment *uniqueFragment =
 				(RangeTableFragment *) lfirst(uniqueFragmentCell);
-			uint64 *uniqueShardId = uniqueFragment->fragmentReference;
+			ShardInterval *uniqueShardInterval =
+				(ShardInterval *) uniqueFragment->fragmentReference;
 
-			if (*shardId == *uniqueShardId)
+			if (shardInterval->shardId == uniqueShardInterval->shardId)
 			{
 				shardIdAlreadyAdded = true;
 				break;
@@ -3734,12 +3738,13 @@ DataFetchTaskList(uint64 jobId, uint32 taskIdIndex, List *fragmentList)
 		RangeTableFragment *fragment = (RangeTableFragment *) lfirst(fragmentCell);
 		if (fragment->fragmentType == CITUS_RTE_RELATION)
 		{
-			uint64 *shardId = fragment->fragmentReference;
+			ShardInterval *shardInterval = fragment->fragmentReference;
-			StringInfo shardFetchQueryString = ShardFetchQueryString(*shardId);
+			uint64 shardId = shardInterval->shardId;
+			StringInfo shardFetchQueryString = ShardFetchQueryString(shardId);
 
 			Task *shardFetchTask = CreateBasicTask(jobId, taskIdIndex, SHARD_FETCH_TASK,
 												   shardFetchQueryString->data);
-			shardFetchTask->shardId = (*shardId);
+			shardFetchTask->shardId = shardId;
 
 			dataFetchTaskList = lappend(dataFetchTaskList, shardFetchTask);
 			taskIdIndex++;
@@ -3969,7 +3974,8 @@ FragmentAlias(RangeTblEntry *rangeTableEntry, RangeTableFragment *fragment)
 	if (fragmentType == CITUS_RTE_RELATION)
 	{
 		char *shardAliasName = NULL;
-		uint64 *shardId = fragment->fragmentReference;
+		ShardInterval *shardInterval = (ShardInterval *) fragment->fragmentReference;
+		uint64 shardId = shardInterval->shardId;
 
 		Oid relationId = rangeTableEntry->relid;
 		char *relationName = get_rel_name(relationId);
@@ -3991,7 +3997,7 @@ FragmentAlias(RangeTblEntry *rangeTableEntry, RangeTableFragment *fragment)
 		 * If user specified a shard name in pg_dist_shard, use that name in alias.
 		 * Otherwise, set shard name in alias to <relation_name>_<shard_id>.
 		 */
-		shardAliasName = LoadShardAlias(relationId, *shardId);
+		shardAliasName = LoadShardAlias(relationId, shardId);
 		if (shardAliasName != NULL)
 		{
 			fragmentName = shardAliasName;
@@ -3999,7 +4005,7 @@ FragmentAlias(RangeTblEntry *rangeTableEntry, RangeTableFragment *fragment)
 		else
 		{
 			char *shardName = pstrdup(relationName);
-			AppendShardIdToName(&shardName, *shardId);
+			AppendShardIdToName(&shardName, shardId);
 
 			fragmentName = shardName;
 		}
@@ -4057,11 +4063,13 @@ AnchorShardId(List *fragmentList, uint32 anchorRangeTableId)
 		RangeTableFragment *fragment = (RangeTableFragment *) lfirst(fragmentCell);
 		if (fragment->rangeTableId == anchorRangeTableId)
 		{
-			uint64 *shardIdPointer = NULL;
+			ShardInterval *shardInterval = NULL;
-			Assert(fragment->fragmentType == CITUS_RTE_RELATION);
 
-			shardIdPointer = (uint64 *) fragment->fragmentReference;
+			Assert(fragment->fragmentType == CITUS_RTE_RELATION);
-			anchorShardId = (*shardIdPointer);
+			Assert(CitusIsA(fragment->fragmentReference, ShardInterval));
+
+			shardInterval = (ShardInterval *) fragment->fragmentReference;
+			anchorShardId = shardInterval->shardId;
 			break;
 		}
 	}