From 52571c00adeddddeca10d32e71104810caf96970 Mon Sep 17 00:00:00 2001
From: Andres Freund <andres@anarazel.de>
Date: Tue, 25 Apr 2017 20:26:40 -0700
Subject: [PATCH] Build DistTableCacheEntry->shardIntervalCompareFunction even
 for 0 shards.

Previously we, unnecessarily, used a the first shard's type
information to to look up the comparison function.  But that
information is already available, so use it.  That's helpful because
we sometimes want to access the comparator function even if there's no
shards.
---
 .../distributed/utils/metadata_cache.c        | 68 ++++---------------
 src/include/distributed/metadata_cache.h      |  2 +-
 2 files changed, 15 insertions(+), 55 deletions(-)

diff --git a/src/backend/distributed/utils/metadata_cache.c b/src/backend/distributed/utils/metadata_cache.c
index a48405597..710526aaa 100644
--- a/src/backend/distributed/utils/metadata_cache.c
+++ b/src/backend/distributed/utils/metadata_cache.c
@@ -134,8 +134,6 @@ static ShardCacheEntry * LookupShardCacheEntry(int64 shardId);
 static DistTableCacheEntry * LookupDistTableCacheEntry(Oid relationId);
 static void BuildDistTableCacheEntry(DistTableCacheEntry *cacheEntry);
 static void BuildCachedShardList(DistTableCacheEntry *cacheEntry);
-static FmgrInfo * ShardIntervalCompareFunction(ShardInterval **shardIntervalArray,
-											   char partitionMethod);
 static ShardInterval ** SortShardIntervalArray(ShardInterval **shardIntervalArray,
 											   int shardCount,
 											   FmgrInfo *
@@ -622,6 +620,10 @@ BuildCachedShardList(DistTableCacheEntry *cacheEntry)
 	List *distShardTupleList = NIL;
 	int shardIntervalArrayLength = 0;
 	int shardIndex = 0;
+	GetPartitionTypeInputInfo(cacheEntry->partitionKeyString,
+							  cacheEntry->partitionMethod,
+							  &intervalTypeId,
+							  &intervalTypeMod);
 
 	distShardTupleList = LookupDistShardTuples(cacheEntry->relationId);
 	shardIntervalArrayLength = list_length(distShardTupleList);
@@ -631,13 +633,6 @@ BuildCachedShardList(DistTableCacheEntry *cacheEntry)
 		TupleDesc distShardTupleDesc = RelationGetDescr(distShardRelation);
 		ListCell *distShardTupleCell = NULL;
 		int arrayIndex = 0;
-		Oid intervalTypeId = InvalidOid;
-		int32 intervalTypeMod = -1;
-
-		GetPartitionTypeInputInfo(cacheEntry->partitionKeyString,
-								  cacheEntry->partitionMethod,
-								  &intervalTypeId,
-								  &intervalTypeMod);
 
 		shardIntervalArray = MemoryContextAllocZero(CacheMemoryContext,
 													shardIntervalArrayLength *
@@ -677,23 +672,19 @@ BuildCachedShardList(DistTableCacheEntry *cacheEntry)
 	}
 
 	/* decide and allocate interval comparison function */
-	if (cacheEntry->partitionMethod == DISTRIBUTE_BY_NONE)
+	if (intervalTypeId != InvalidOid)
+	{
+		/* allocate the comparison function in the cache context */
+		MemoryContext oldContext = MemoryContextSwitchTo(CacheMemoryContext);
+
+		shardIntervalCompareFunction = GetFunctionInfo(intervalTypeId, BTREE_AM_OID,
+													   BTORDER_PROC);
+		MemoryContextSwitchTo(oldContext);
+	}
+	else
 	{
 		shardIntervalCompareFunction = NULL;
 	}
-	else if (shardIntervalArrayLength > 0)
-	{
-		MemoryContext oldContext = CurrentMemoryContext;
-
-		/* allocate the comparison function in the cache context */
-		oldContext = MemoryContextSwitchTo(CacheMemoryContext);
-
-		shardIntervalCompareFunction =
-			ShardIntervalCompareFunction(shardIntervalArray,
-										 cacheEntry->partitionMethod);
-
-		MemoryContextSwitchTo(oldContext);
-	}
 
 	/* reference tables has a single shard which is not initialized */
 	if (cacheEntry->partitionMethod == DISTRIBUTE_BY_NONE)
@@ -798,37 +789,6 @@ BuildCachedShardList(DistTableCacheEntry *cacheEntry)
 }
 
 
-/*
- * ShardIntervalCompareFunction returns the appropriate compare function for the
- * partition column type. In case of hash-partitioning, it always returns the compare
- * function for integers. Callers of this function has to ensure that shardIntervalArray
- * has at least one element.
- */
-static FmgrInfo *
-ShardIntervalCompareFunction(ShardInterval **shardIntervalArray, char partitionMethod)
-{
-	FmgrInfo *shardIntervalCompareFunction = NULL;
-	Oid comparisonTypeId = InvalidOid;
-
-	Assert(shardIntervalArray != NULL);
-
-	if (partitionMethod == DISTRIBUTE_BY_HASH)
-	{
-		comparisonTypeId = INT4OID;
-	}
-	else
-	{
-		ShardInterval *shardInterval = shardIntervalArray[0];
-		comparisonTypeId = shardInterval->valueTypeId;
-	}
-
-	shardIntervalCompareFunction = GetFunctionInfo(comparisonTypeId, BTREE_AM_OID,
-												   BTORDER_PROC);
-
-	return shardIntervalCompareFunction;
-}
-
-
 /*
  * SortedShardIntervalArray sorts the input shardIntervalArray. Shard intervals with
  * no min/max values are placed at the end of the array.
diff --git a/src/include/distributed/metadata_cache.h b/src/include/distributed/metadata_cache.h
index 24324aa56..d80b4a038 100644
--- a/src/include/distributed/metadata_cache.h
+++ b/src/include/distributed/metadata_cache.h
@@ -49,7 +49,7 @@ typedef struct
 	int shardIntervalArrayLength;
 	ShardInterval **sortedShardIntervalArray;
 
-	FmgrInfo *shardIntervalCompareFunction; /* NULL if no shard intervals exist */
+	FmgrInfo *shardIntervalCompareFunction;  /* NULL if DISTRIBUTE_BY_NONE */
 	FmgrInfo *hashFunction; /* NULL if table is not distributed by hash */
 
 	/* pg_dist_shard_placement metadata */