Add infrastructure to hide shards on MX worker nodes

Add ability to understand whether a table is a
known shard on MX workers. Note that this is only useful
and applicable for hiding shards on MX worker nodes given
that we can have metadata only there.

src/backend/distributed/worker/worker_data_fetch_protocol.c

@@ -62,7 +62,6 @@ static bool ReceiveRegularFile(const char *nodeName, uint32 nodePort,
 static void ReceiveResourceCleanup(int32 connectionId, const char *filename,
 								   int32 fileDescriptor);
 static void CitusDeleteFile(const char *filename);
-static uint64 ExtractShardId(const char *tableName);
 static bool check_log_statement(List *stmt_list);
 static void AlterSequenceMinMax(Oid sequenceId, char *schemaName, char *sequenceName);
 static void SetDefElemArg(AlterSeqStmt *statement, const char *name, Node *arg);
@@ -526,9 +525,13 @@ worker_apply_sequence_command(PG_FUNCTION_ARGS)
 }
 
 
-/* Extracts shard id from the given table name, and returns it. */
+/*
-static uint64
+ * ExtractShardId tries to extract shard id from the given table name,
-ExtractShardId(const char *tableName)
+ * and returns the shard id if table name is formatted as shard name.
+ * Else, the function returns INVALID_SHARD_ID.
+ */
+uint64
+ExtractShardId(const char *tableName, bool missingOk)
 {
 	uint64 shardId = 0;
 	char *shardIdString = NULL;
@@ -536,11 +539,16 @@ ExtractShardId(const char *tableName)
 
 	/* find the last underscore and increment for shardId string */
 	shardIdString = strrchr(tableName, SHARD_NAME_SEPARATOR);
-	if (shardIdString == NULL)
+	if (shardIdString == NULL && !missingOk)
 	{
 		ereport(ERROR, (errmsg("could not extract shardId from table name \"%s\"",
 							   tableName)));
 	}
+	else if (shardIdString == NULL && missingOk)
+	{
+		return INVALID_SHARD_ID;
+	}
+
 	shardIdString++;
 
 	errno = 0;
@@ -548,8 +556,15 @@ ExtractShardId(const char *tableName)
 
 	if (errno != 0 || (*shardIdStringEnd != '\0'))
 	{
-		ereport(ERROR, (errmsg("could not extract shardId from table name \"%s\"",
+		if (!missingOk)
-							   tableName)));
+		{
+			ereport(ERROR, (errmsg("could not extract shardId from table name \"%s\"",
+								   tableName)));
+		}
+		else
+		{
+			return INVALID_SHARD_ID;
+		}
 	}
 
 	return shardId;
@@ -761,7 +776,7 @@ worker_append_table_to_shard(PG_FUNCTION_ARGS)
 	 * the transaction for this function commits, this lock will automatically
 	 * be released. This ensures appends to a shard happen in a serial manner.
 	 */
-	shardId = ExtractShardId(shardTableName);
+	shardId = ExtractShardId(shardTableName, false);
 	LockShardResource(shardId, AccessExclusiveLock);
 
 	/* copy remote table's data to this node */

src/backend/distributed/worker/worker_shard_visibility.c

@@ -0,0 +1,118 @@
+/*
+ * worker_shard_visibility.c
+ *
+ * TODO: Write some meaningful comment
+ */
+
+#include "postgres.h"
+
+#include "catalog/namespace.h"
+#include "distributed/metadata_cache.h"
+#include "distributed/worker_protocol.h"
+#include "utils/lsyscache.h"
+
+
+PG_FUNCTION_INFO_V1(relation_is_a_known_shard);
+
+
+static bool RelationIsAKnownShard(Oid shardRelationId);
+
+
+Datum
+relation_is_a_known_shard(PG_FUNCTION_ARGS)
+{
+	Oid relationId = PG_GETARG_OID(0);
+
+	PG_RETURN_BOOL(RelationIsAKnownShard(relationId));
+}
+
+/*
+ * Given a relationId, check whether it's a shard of any distributed table.
+ * We can only do that in MX since we've metadata there. We can actually
+ * implement for non-mx as well, but, there is currently no need for that.
+ *
+ * TODO: improve the comment
+ * TODO: Make sure that we're not missing any edge cases with our
+ * 		 implementation
+ */
+bool
+RelationIsAKnownShard(Oid shardRelationId)
+{
+	int localGroupId = -1;
+	char *shardRelationName = NULL;
+	char *relationName = NULL;
+	bool missingOk = true;
+	uint64 shardId = INVALID_SHARD_ID;
+	ShardInterval *shardInterval = NULL;
+	Oid relationId = InvalidOid;
+	char *shardIdString = NULL;
+	int relationNameLength = 0;
+
+
+	/*
+	 * TODO: version check
+	 */
+
+	if (!OidIsValid(shardRelationId))
+	{
+		/* we cannot continue without a valid Oid */
+		return false;
+	}
+
+	localGroupId = GetLocalGroupId();
+	if (localGroupId == 0)
+	{
+		/*
+		 * We're not interested in shards in the coordinator
+		 * or non-mx worker nodes.
+		*/
+		return false;
+	}
+
+	shardRelationName = get_rel_name(shardRelationId);
+
+	/* find the last underscore and increment for shardId string */
+	shardIdString = strrchr(shardRelationName, SHARD_NAME_SEPARATOR);
+	if (shardIdString == NULL)
+	{
+		return false;
+	}
+
+	relationNameLength = shardIdString - shardRelationName;
+	relationName = strndup(shardRelationName, relationNameLength);
+
+	relationId = RelnameGetRelid(relationName);
+	if (!OidIsValid(relationId))
+	{
+		/* there is no such relation */
+		return false;
+	}
+
+	if (!IsDistributedTable(relationId))
+	{
+		/* we're  obviously only interested in distributed tables */
+		return false;
+	}
+
+	shardId = ExtractShardId(shardRelationName, missingOk);
+	if (shardId == INVALID_SHARD_ID)
+	{
+		/*
+		 * The format of the table name does not align with
+		 * our shard name definition.
+		 */
+		return false;
+	}
+
+	/*
+	 * At this point we're sure that this is a shard of a
+	 * distributed table.
+	 */
+	shardInterval = LoadShardInterval(shardId);
+	if (shardInterval->relationId == relationId)
+	{
+		return true;
+	}
+
+	return false;
+}

src/include/distributed/worker_protocol.h

@@ -120,6 +120,8 @@ extern int32 ArrayObjectCount(ArrayType *arrayObject);
 extern FmgrInfo * GetFunctionInfo(Oid typeId, Oid accessMethodId, int16 procedureId);
 extern List * TableDDLCommandList(const char *nodeName, uint32 nodePort,
 								  const char *tableName);
+extern uint64 ExtractShardId(const char *tableName, bool missingOk);
+
 
 /* Function declarations shared with the master planner */
 extern StringInfo TaskFilename(StringInfo directoryName, uint32 taskId);