mirror of https://github.com/citusdata/citus.git
WorkerGetRandomCandidateNode only returns primary nodes
Brian Cloutier
parent
b081fb0efa
commit
8260fcddbd
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@ -38,11 +38,12 @@ int MaxWorkerNodesTracked = 2048; /* determines worker node hash table size *
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/* Local functions forward declarations */
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static char * ClientHostAddress(StringInfo remoteHostStringInfo);
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static WorkerNode * FindRandomNodeNotInList(HTAB *WorkerNodesHash,
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List *currentNodeList);
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static WorkerNode * FindRandomNodeFromList(List *workerNodeList);
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static bool OddNumber(uint32 number);
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static bool ListMember(List *currentList, WorkerNode *workerNode);
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static List * PrimaryNodesNotInList(List *currentList);
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/* ------------------------------------------------------------
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* Worker node selection functions follow
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@ -65,16 +66,15 @@ WorkerGetRandomCandidateNode(List *currentNodeList)
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uint32 tryCount = WORKER_RACK_TRIES;
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uint32 tryIndex = 0;
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HTAB *workerNodeHash = GetWorkerNodeHash();
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uint32 currentNodeCount = list_length(currentNodeList);
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List *candidateWorkerNodeList = PrimaryNodesNotInList(currentNodeList);
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/*
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* We check if the shard has already been placed on all nodes known to us.
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* This check is rather defensive, and has the drawback of performing a full
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* scan over the worker node hash for determining the number of live nodes.
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* scan over the worker node hash.
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*/
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uint32 currentNodeCount = list_length(currentNodeList);
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uint32 liveNodeCount = WorkerGetLiveNodeCount();
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if (currentNodeCount >= liveNodeCount)
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if (list_length(candidateWorkerNodeList) == 0)
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{
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return NULL;
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}
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@ -82,7 +82,7 @@ WorkerGetRandomCandidateNode(List *currentNodeList)
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/* if current node list is empty, randomly pick one node and return */
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if (currentNodeCount == 0)
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{
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workerNode = FindRandomNodeNotInList(workerNodeHash, NIL);
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workerNode = FindRandomNodeFromList(candidateWorkerNodeList);
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return workerNode;
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}
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@ -112,7 +112,7 @@ WorkerGetRandomCandidateNode(List *currentNodeList)
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char *workerRack = NULL;
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bool sameRack = false;
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workerNode = FindRandomNodeNotInList(workerNodeHash, currentNodeList);
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workerNode = FindRandomNodeFromList(candidateWorkerNodeList);
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workerRack = workerNode->workerRack;
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sameRack = (strncmp(workerRack, firstRack, WORKER_LENGTH) == 0);
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@ -328,13 +328,14 @@ WorkerNodeList(void)
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while ((workerNode = hash_seq_search(&status)) != NULL)
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{
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WorkerNode *workerNodeCopy = palloc0(sizeof(WorkerNode));
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WorkerNode *workerNodeCopy;
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if (workerNode->nodeRole != NODE_ROLE_PRIMARY)
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{
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continue;
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}
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workerNodeCopy = palloc0(sizeof(WorkerNode));
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memcpy(workerNodeCopy, workerNode, sizeof(WorkerNode));
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workerNodeList = lappend(workerNodeList, workerNodeCopy);
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}
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@ -344,70 +345,50 @@ WorkerNodeList(void)
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/*
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* FindRandomNodeNotInList finds a random node from the shared hash that is not
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* a member of the current node list. The caller is responsible for making the
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* necessary node count checks to ensure that such a node exists.
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*
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* Note that this function has a selection bias towards nodes whose positions in
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* the shared hash are sequentially adjacent to the positions of nodes that are
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* in the current node list. This bias follows from our decision to first pick a
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* random node in the hash, and if that node is a member of the current list, to
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* simply iterate to the next node in the hash. Overall, this approach trades in
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* some selection bias for simplicity in design and for bounded execution time.
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* WorkerNodesNotInList scans through the worker node hash and returns a list
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* of all primary nodes which are not in currentList.
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*/
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static WorkerNode *
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FindRandomNodeNotInList(HTAB *WorkerNodesHash, List *currentNodeList)
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static List *
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PrimaryNodesNotInList(List *currentList)
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{
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List *workerNodeList = NIL;
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HTAB *workerNodeHash = GetWorkerNodeHash();
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WorkerNode *workerNode = NULL;
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HASH_SEQ_STATUS status;
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uint32 workerNodeCount = 0;
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uint32 currentNodeCount PG_USED_FOR_ASSERTS_ONLY = 0;
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bool lookForWorkerNode = true;
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uint32 workerPosition = 0;
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uint32 workerIndex = 0;
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workerNodeCount = hash_get_num_entries(WorkerNodesHash);
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currentNodeCount = list_length(currentNodeList);
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Assert(workerNodeCount > currentNodeCount);
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hash_seq_init(&status, workerNodeHash);
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/*
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* We determine a random position within the worker hash between [1, N],
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* assuming that the number of elements in the hash is N. We then get to
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* this random position by iterating over the worker hash. Please note that
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* the random seed has already been set by the postmaster when starting up.
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*/
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workerPosition = (random() % workerNodeCount) + 1;
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hash_seq_init(&status, WorkerNodesHash);
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for (workerIndex = 0; workerIndex < workerPosition; workerIndex++)
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/* this is O(n*m) but there usually aren't many nodes in currentList */
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while ((workerNode = hash_seq_search(&status)) != NULL)
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{
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workerNode = (WorkerNode *) hash_seq_search(&status);
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WorkerNode *workerNodeCopy;
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if ((workerNode->nodeRole != NODE_ROLE_PRIMARY) ||
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ListMember(currentList, workerNode))
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{
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continue;
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}
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while (lookForWorkerNode)
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{
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bool listMember = ListMember(currentNodeList, workerNode);
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if (!listMember)
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{
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lookForWorkerNode = false;
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}
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else
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{
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/* iterate to the next worker node in the hash */
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workerNode = (WorkerNode *) hash_seq_search(&status);
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/* reached end of hash; start from the beginning */
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if (workerNode == NULL)
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{
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hash_seq_init(&status, WorkerNodesHash);
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workerNode = (WorkerNode *) hash_seq_search(&status);
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}
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}
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workerNodeCopy = palloc0(sizeof(WorkerNode));
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memcpy(workerNodeCopy, workerNode, sizeof(WorkerNode));
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workerNodeList = lappend(workerNodeList, workerNodeCopy);
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}
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/* we stopped scanning before completion; therefore clean up scan */
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hash_seq_term(&status);
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return workerNodeList;
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}
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/* FindRandomNodeFromList picks a random node from the list provided to it */
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static WorkerNode *
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FindRandomNodeFromList(List *candidateWorkerNodeList)
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{
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uint32 candidateNodeCount = list_length(candidateWorkerNodeList);
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/* nb, the random seed has already been set by the postmaster when starting up. */
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uint32 workerPosition = (random() % candidateNodeCount);
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WorkerNode *workerNode = (WorkerNode *) list_nth(candidateWorkerNodeList,
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workerPosition);
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return workerNode;
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}
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