/*
* lock_shard_resources allows shard resources to be locked
* remotely to serialise non-commutative writes on shards.
*
* This function does not sort the array to avoid deadlock, callers
* must ensure a consistent order.
*/
Datum
lock_shard_resources(PG_FUNCTION_ARGS)
{
LOCKMODE lockMode = IntToLockMode(PG_GETARG_INT32(0));
ArrayType *shardIdArrayObject = PG_GETARG_ARRAYTYPE_P(1);
Datum *shardIdArrayDatum = NULL;
int shardIdCount = 0;
int shardIdIndex = 0;
if (ARR_NDIM(shardIdArrayObject) == 0)
{
ereport(ERROR, (errmsg("no locks specified")));
}
/* we don't want random users to block writes */
EnsureSuperUser();
shardIdCount = ArrayObjectCount(shardIdArrayObject);
shardIdArrayDatum = DeconstructArrayObject(shardIdArrayObject);
for (shardIdIndex = 0; shardIdIndex < shardIdCount; shardIdIndex++)
{
int64 shardId = DatumGetInt64(shardIdArrayDatum[shardIdIndex]);
LockShardResource(shardId, lockMode);
}
PG_RETURN_VOID();
}
/* Creates a list of cstrings from a single dimensional array object. */
static List *
ArrayObjectToCStringList(ArrayType *arrayObject)
{
List *cstringList = NIL;
Datum *datumArray = DeconstructArrayObject(arrayObject);
int32 arraySize = ArrayObjectCount(arrayObject);
int32 arrayIndex = 0;
for (arrayIndex = 0; arrayIndex < arraySize; arrayIndex++)
{
Datum datum = datumArray[arrayIndex];
char *cstring = TextDatumGetCString(datum);
cstringList = lappend(cstringList, cstring);
}
Assert(cstringList != NIL);
return cstringList;
}
/*
* FetchTableCommon executes common logic that wraps around the actual data
* fetching function. This common logic includes ensuring that only one process
* tries to fetch this table at any given time, and that data fetch operations
* are retried in case of node failures.
*/
static void
FetchTableCommon(text *tableNameText, uint64 remoteTableSize,
ArrayType *nodeNameObject, ArrayType *nodePortObject,
bool (*FetchTableFunction)(const char *, uint32, const char *))
{
uint64 shardId = INVALID_SHARD_ID;
Oid relationId = InvalidOid;
List *relationNameList = NIL;
RangeVar *relation = NULL;
uint32 nodeIndex = 0;
bool tableFetched = false;
char *tableName = text_to_cstring(tableNameText);
Datum *nodeNameArray = DeconstructArrayObject(nodeNameObject);
Datum *nodePortArray = DeconstructArrayObject(nodePortObject);
int32 nodeNameCount = ArrayObjectCount(nodeNameObject);
int32 nodePortCount = ArrayObjectCount(nodePortObject);
/* we should have the same number of node names and port numbers */
if (nodeNameCount != nodePortCount)
{
ereport(ERROR, (errmsg("node name array size: %d and node port array size: %d"
" do not match", nodeNameCount, nodePortCount)));
}
/*
* We lock on the shardId, but do not unlock. When the function returns, and
* the transaction for this function commits, this lock will automatically
* be released. This ensures that concurrent caching commands will see the
* newly created table when they acquire the lock (in read committed mode).
*/
shardId = ExtractShardId(tableName);
LockShardResource(shardId, AccessExclusiveLock);
relationNameList = textToQualifiedNameList(tableNameText);
relation = makeRangeVarFromNameList(relationNameList);
relationId = RangeVarGetRelid(relation, NoLock, true);
/* check if we already fetched the table */
if (relationId != InvalidOid)
{
uint64 localTableSize = 0;
if (!ExpireCachedShards)
{
return;
}
/*
* Check if the cached shard has the same size on disk as it has as on
* the placement (is up to date).
*
* Note 1: performing updates or deletes on the original shard leads to
* inconsistent sizes between different databases in which case the data
* would be fetched every time, or worse, the placement would get into
* a deadlock when it tries to fetch from itself while holding the lock.
* Therefore, this option is disabled by default.
*
* Note 2: when appending data to a shard, the size on disk only
* increases when a new page is added (the next 8kB block).
*/
localTableSize = LocalTableSize(relationId);
if (remoteTableSize > localTableSize)
{
/* table is not up to date, drop the table */
ObjectAddress tableObject = { InvalidOid, InvalidOid, 0 };
tableObject.classId = RelationRelationId;
tableObject.objectId = relationId;
tableObject.objectSubId = 0;
performDeletion(&tableObject, DROP_RESTRICT, PERFORM_DELETION_INTERNAL);
}
else
{
/* table is up to date */
return;
}
}
/* loop until we fetch the table or try all nodes */
while (!tableFetched && (nodeIndex < nodeNameCount))
{
Datum nodeNameDatum = nodeNameArray[nodeIndex];
Datum nodePortDatum = nodePortArray[nodeIndex];
char *nodeName = TextDatumGetCString(nodeNameDatum);
uint32 nodePort = DatumGetUInt32(nodePortDatum);
tableFetched = (*FetchTableFunction)(nodeName, nodePort, tableName);
nodeIndex++;
}
/* error out if we tried all nodes and could not fetch the table */
if (!tableFetched)
{
ereport(ERROR, (errmsg("could not fetch relation: \"%s\"", tableName)));
}
}
