void updateChunkWriteStatsAndSplitIfNeeded(OperationContext* opCtx,
ChunkManager* manager,
Chunk* chunk,
long dataWritten) {
// Disable lastError tracking so that any errors, which occur during auto-split do not get
// bubbled up on the client connection doing a write.
LastError::Disabled d(&LastError::get(cc()));
const auto balancerConfig = Grid::get(opCtx)->getBalancerConfiguration();
const bool minIsInf =
(0 == manager->getShardKeyPattern().getKeyPattern().globalMin().woCompare(chunk->getMin()));
const bool maxIsInf =
(0 == manager->getShardKeyPattern().getKeyPattern().globalMax().woCompare(chunk->getMax()));
const uint64_t chunkBytesWritten = chunk->addBytesWritten(dataWritten);
const uint64_t desiredChunkSize =
calculateDesiredChunkSize(balancerConfig->getMaxChunkSizeBytes(), manager->numChunks());
if (!chunk->shouldSplit(desiredChunkSize, minIsInf, maxIsInf)) {
return;
}
const NamespaceString nss(manager->getns());
if (!manager->_autoSplitThrottle._splitTickets.tryAcquire()) {
LOG(1) << "won't auto split because not enough tickets: " << nss;
return;
}
TicketHolderReleaser releaser(&(manager->_autoSplitThrottle._splitTickets));
const ChunkRange chunkRange(chunk->getMin(), chunk->getMax());
try {
// Ensure we have the most up-to-date balancer configuration
uassertStatusOK(balancerConfig->refreshAndCheck(opCtx));
if (!balancerConfig->getShouldAutoSplit()) {
return;
}
LOG(1) << "about to initiate autosplit: " << redact(chunk->toString())
<< " dataWritten: " << chunkBytesWritten
<< " desiredChunkSize: " << desiredChunkSize;
const uint64_t chunkSizeToUse = [&]() {
const uint64_t estNumSplitPoints = chunkBytesWritten / desiredChunkSize * 2;
if (estNumSplitPoints >= kTooManySplitPoints) {
// The current desired chunk size will split the chunk into lots of small chunk and
// at the worst case this can result into thousands of chunks. So check and see if a
// bigger value can be used.
return std::min(chunkBytesWritten, balancerConfig->getMaxChunkSizeBytes());
} else {
return desiredChunkSize;
}
}();
auto splitPoints =
uassertStatusOK(shardutil::selectChunkSplitPoints(opCtx,
chunk->getShardId(),
nss,
manager->getShardKeyPattern(),
chunkRange,
chunkSizeToUse,
boost::none));
if (splitPoints.size() <= 1) {
// No split points means there isn't enough data to split on; 1 split point means we
// have
// between half the chunk size to full chunk size so there is no need to split yet
chunk->clearBytesWritten();
return;
}
if (minIsInf || maxIsInf) {
// We don't want to reset _dataWritten since we want to check the other side right away
} else {
// We're splitting, so should wait a bit
chunk->clearBytesWritten();
}
// We assume that if the chunk being split is the first (or last) one on the collection,
// this chunk is likely to see more insertions. Instead of splitting mid-chunk, we use the
// very first (or last) key as a split point.
//
// This heuristic is skipped for "special" shard key patterns that are not likely to produce
// monotonically increasing or decreasing values (e.g. hashed shard keys).
if (KeyPattern::isOrderedKeyPattern(manager->getShardKeyPattern().toBSON())) {
if (minIsInf) {
BSONObj key = findExtremeKeyForShard(
opCtx, nss, chunk->getShardId(), manager->getShardKeyPattern(), true);
if (!key.isEmpty()) {
splitPoints.front() = key.getOwned();
}
} else if (maxIsInf) {
BSONObj key = findExtremeKeyForShard(
opCtx, nss, chunk->getShardId(), manager->getShardKeyPattern(), false);
if (!key.isEmpty()) {
splitPoints.back() = key.getOwned();
}
}
}
const auto suggestedMigrateChunk =
uassertStatusOK(shardutil::splitChunkAtMultiplePoints(opCtx,
chunk->getShardId(),
nss,
manager->getShardKeyPattern(),
manager->getVersion(),
chunkRange,
splitPoints));
// Balance the resulting chunks if the option is enabled and if the shard suggested a chunk
// to balance
const bool shouldBalance = [&]() {
if (!balancerConfig->shouldBalanceForAutoSplit())
return false;
auto collStatus =
Grid::get(opCtx)->catalogClient()->getCollection(opCtx, manager->getns());
if (!collStatus.isOK()) {
log() << "Auto-split for " << nss << " failed to load collection metadata"
<< causedBy(redact(collStatus.getStatus()));
return false;
}
return collStatus.getValue().value.getAllowBalance();
}();
log() << "autosplitted " << nss << " chunk: " << redact(chunk->toString()) << " into "
<< (splitPoints.size() + 1) << " parts (desiredChunkSize " << desiredChunkSize << ")"
<< (suggestedMigrateChunk ? "" : (std::string) " (migrate suggested" +
(shouldBalance ? ")" : ", but no migrations allowed)"));
// Reload the chunk manager after the split
auto routingInfo = uassertStatusOK(
Grid::get(opCtx)->catalogCache()->getShardedCollectionRoutingInfoWithRefresh(opCtx,
nss));
if (!shouldBalance || !suggestedMigrateChunk) {
return;
}
// Top chunk optimization - try to move the top chunk out of this shard to prevent the hot
// spot from staying on a single shard. This is based on the assumption that succeeding
// inserts will fall on the top chunk.
// We need to use the latest chunk manager (after the split) in order to have the most
// up-to-date view of the chunk we are about to move
auto suggestedChunk = routingInfo.cm()->findIntersectingChunkWithSimpleCollation(
suggestedMigrateChunk->getMin());
ChunkType chunkToMove;
chunkToMove.setNS(nss.ns());
chunkToMove.setShard(suggestedChunk->getShardId());
chunkToMove.setMin(suggestedChunk->getMin());
chunkToMove.setMax(suggestedChunk->getMax());
chunkToMove.setVersion(suggestedChunk->getLastmod());
uassertStatusOK(configsvr_client::rebalanceChunk(opCtx, chunkToMove));
// Ensure the collection gets reloaded because of the move
Grid::get(opCtx)->catalogCache()->invalidateShardedCollection(nss);
} catch (const DBException& ex) {
chunk->clearBytesWritten();
if (ErrorCodes::isStaleShardingError(ErrorCodes::Error(ex.getCode()))) {
log() << "Unable to auto-split chunk " << redact(chunkRange.toString()) << causedBy(ex)
<< ", going to invalidate routing table entry for " << nss;
Grid::get(opCtx)->catalogCache()->invalidateShardedCollection(nss);
}
}
}
void ChunkSplitter::_runAutosplit(const NamespaceString& nss,
const BSONObj& min,
const BSONObj& max,
long dataWritten) {
if (!_isPrimary) {
return;
}
try {
const auto opCtx = cc().makeOperationContext();
const auto routingInfo = uassertStatusOK(
Grid::get(opCtx.get())->catalogCache()->getCollectionRoutingInfo(opCtx.get(), nss));
uassert(ErrorCodes::NamespaceNotSharded,
"Could not split chunk. Collection is no longer sharded",
routingInfo.cm());
const auto cm = routingInfo.cm();
const auto chunk = cm->findIntersectingChunkWithSimpleCollation(min);
// Stop if chunk's range differs from the range we were expecting to split.
if ((0 != chunk.getMin().woCompare(min)) || (0 != chunk.getMax().woCompare(max)) ||
(chunk.getShardId() != ShardingState::get(opCtx.get())->getShardName())) {
LOG(1) << "Cannot auto-split chunk with range '"
<< redact(ChunkRange(min, max).toString()) << "' for nss '" << nss
<< "' on shard '" << ShardingState::get(opCtx.get())->getShardName()
<< "' because since scheduling auto-split the chunk has been changed to '"
<< redact(chunk.toString()) << "'";
return;
}
const ChunkRange chunkRange(chunk.getMin(), chunk.getMax());
const auto balancerConfig = Grid::get(opCtx.get())->getBalancerConfiguration();
// Ensure we have the most up-to-date balancer configuration
uassertStatusOK(balancerConfig->refreshAndCheck(opCtx.get()));
if (!balancerConfig->getShouldAutoSplit()) {
return;
}
const uint64_t maxChunkSizeBytes = balancerConfig->getMaxChunkSizeBytes();
LOG(1) << "about to initiate autosplit: " << redact(chunk.toString())
<< " dataWritten since last check: " << dataWritten
<< " maxChunkSizeBytes: " << maxChunkSizeBytes;
auto splitPoints = uassertStatusOK(splitVector(opCtx.get(),
nss,
cm->getShardKeyPattern().toBSON(),
chunk.getMin(),
chunk.getMax(),
false,
boost::none,
boost::none,
boost::none,
maxChunkSizeBytes));
if (splitPoints.size() <= 1) {
// No split points means there isn't enough data to split on; 1 split point means we
// have between half the chunk size to full chunk size so there is no need to split yet
return;
}
// We assume that if the chunk being split is the first (or last) one on the collection,
// this chunk is likely to see more insertions. Instead of splitting mid-chunk, we use the
// very first (or last) key as a split point.
//
// This heuristic is skipped for "special" shard key patterns that are not likely to produce
// monotonically increasing or decreasing values (e.g. hashed shard keys).
// Keeps track of the minKey of the top chunk after the split so we can migrate the chunk.
BSONObj topChunkMinKey;
if (KeyPattern::isOrderedKeyPattern(cm->getShardKeyPattern().toBSON())) {
if (0 ==
cm->getShardKeyPattern().getKeyPattern().globalMin().woCompare(chunk.getMin())) {
// MinKey is infinity (This is the first chunk on the collection)
BSONObj key =
findExtremeKeyForShard(opCtx.get(), nss, cm->getShardKeyPattern(), true);
if (!key.isEmpty()) {
splitPoints.front() = key.getOwned();
topChunkMinKey = cm->getShardKeyPattern().getKeyPattern().globalMin();
}
} else if (0 ==
cm->getShardKeyPattern().getKeyPattern().globalMax().woCompare(
chunk.getMax())) {
// MaxKey is infinity (This is the last chunk on the collection)
BSONObj key =
findExtremeKeyForShard(opCtx.get(), nss, cm->getShardKeyPattern(), false);
if (!key.isEmpty()) {
splitPoints.back() = key.getOwned();
topChunkMinKey = key.getOwned();
}
}
}
uassertStatusOK(splitChunkAtMultiplePoints(opCtx.get(),
chunk.getShardId(),
nss,
cm->getShardKeyPattern(),
cm->getVersion(),
chunkRange,
splitPoints));
const bool shouldBalance = isAutoBalanceEnabled(opCtx.get(), nss, balancerConfig);
log() << "autosplitted " << nss << " chunk: " << redact(chunk.toString()) << " into "
<< (splitPoints.size() + 1) << " parts (maxChunkSizeBytes " << maxChunkSizeBytes
<< ")"
<< (topChunkMinKey.isEmpty() ? "" : " (top chunk migration suggested" +
(std::string)(shouldBalance ? ")" : ", but no migrations allowed)"));
// Balance the resulting chunks if the autobalance option is enabled and if we split at the
// first or last chunk on the collection as part of top chunk optimization.
if (!shouldBalance || topChunkMinKey.isEmpty()) {
return;
}
// Tries to move the top chunk out of the shard to prevent the hot spot from staying on a
// single shard. This is based on the assumption that succeeding inserts will fall on the
// top chunk.
moveChunk(opCtx.get(), nss, topChunkMinKey);
} catch (const DBException& ex) {
log() << "Unable to auto-split chunk " << redact(ChunkRange(min, max).toString())
<< " in nss " << nss << causedBy(redact(ex.toStatus()));
} catch (const std::exception& e) {
log() << "caught exception while splitting chunk: " << redact(e.what());
}
}