StatusWith<MigrateInfoVector> BalancerChunkSelectionPolicyImpl::_getMigrateCandidatesForCollection(
OperationContext* txn,
const NamespaceString& nss,
const ShardStatisticsVector& shardStats,
bool aggressiveBalanceHint) {
auto scopedCMStatus = ScopedChunkManager::getExisting(txn, nss);
if (!scopedCMStatus.isOK()) {
return scopedCMStatus.getStatus();
}
auto scopedCM = std::move(scopedCMStatus.getValue());
ChunkManager* const cm = scopedCM.cm();
auto collInfoStatus = createCollectionDistributionInfo(txn, shardStats, cm);
if (!collInfoStatus.isOK()) {
return collInfoStatus.getStatus();
}
auto collInfo = std::move(collInfoStatus.getValue());
DistributionStatus distribution = std::move(std::get<0>(collInfo));
ChunkMinimumsSet allChunkMinimums = std::move(std::get<1>(collInfo));
for (const auto& tagRangeEntry : distribution.tagRanges()) {
const auto& tagRange = tagRangeEntry.second;
if (!allChunkMinimums.count(tagRange.min)) {
// This tag falls somewhere at the middle of a chunk. Therefore we must skip balancing
// this collection until it is split at the next iteration.
//
// TODO: We should be able to just skip chunks, which straddle tags and still make some
// progress balancing.
return {ErrorCodes::IllegalOperation,
str::stream()
<< "Tag boundaries "
<< tagRange.toString()
<< " fall in the middle of an existing chunk. Balancing for collection "
<< nss.ns()
<< " will be postponed until the chunk is split appropriately."};
}
}
return BalancerPolicy::balance(shardStats, distribution, aggressiveBalanceHint);
}
StatusWith<SplitInfoVector> BalancerChunkSelectionPolicyImpl::_getSplitCandidatesForCollection(
OperationContext* txn, const NamespaceString& nss, const ShardStatisticsVector& shardStats) {
auto scopedCMStatus = ScopedChunkManager::getExisting(txn, nss);
if (!scopedCMStatus.isOK()) {
return scopedCMStatus.getStatus();
}
auto scopedCM = std::move(scopedCMStatus.getValue());
ChunkManager* const cm = scopedCM.cm();
auto collInfoStatus = createCollectionDistributionInfo(txn, shardStats, cm);
if (!collInfoStatus.isOK()) {
return collInfoStatus.getStatus();
}
auto collInfo = std::move(collInfoStatus.getValue());
DistributionStatus distribution = std::move(std::get<0>(collInfo));
ChunkMinimumsSet allChunkMinimums = std::move(std::get<1>(collInfo));
SplitInfoVector splitCandidates;
// Accumulate split points for the same chunk together
shared_ptr<Chunk> currentChunk;
vector<BSONObj> currentSplitVector;
for (const auto& tagRangeEntry : distribution.tagRanges()) {
const auto& tagRange = tagRangeEntry.second;
if (allChunkMinimums.count(tagRange.min)) {
continue;
}
shared_ptr<Chunk> chunk = cm->findIntersectingChunkWithSimpleCollation(txn, tagRange.min);
if (!currentChunk) {
currentChunk = chunk;
}
invariant(currentChunk);
if (chunk == currentChunk) {
currentSplitVector.push_back(tagRange.min);
} else {
splitCandidates.emplace_back(currentChunk->getShardId(),
nss,
cm->getVersion(),
currentChunk->getLastmod(),
currentChunk->getMin(),
currentChunk->getMax(),
std::move(currentSplitVector));
currentChunk = chunk;
currentSplitVector.push_back(tagRange.min);
}
}
// Drain the current split vector if there are any entries left
if (currentChunk) {
invariant(!currentSplitVector.empty());
splitCandidates.emplace_back(currentChunk->getShardId(),
nss,
cm->getVersion(),
currentChunk->getLastmod(),
currentChunk->getMin(),
currentChunk->getMax(),
std::move(currentSplitVector));
}
return splitCandidates;
}
