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/**
* Copyright (C) 2017 MongoDB Inc.
*
* This program is free software: you can redistribute it and/or modify
* it under the terms of the GNU Affero General Public License, version 3,
* as published by the Free Software Foundation.
*
* This program is distributed in the hope that it will be useful,
* but WITHOUT ANY WARRANTY; without even the implied warranty of
* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
* GNU Affero General Public License for more details.
*
* You should have received a copy of the GNU Affero General Public License
* along with this program. If not, see <http://www.gnu.org/licenses/>.
*
* As a special exception, the copyright holders give permission to link the
* code of portions of this program with the OpenSSL library under certain
* conditions as described in each individual source file and distribute
* linked combinations including the program with the OpenSSL library. You
* must comply with the GNU Affero General Public License in all respects for
* all of the code used other than as permitted herein. If you modify file(s)
* with this exception, you may extend this exception to your version of the
* file(s), but you are not obligated to do so. If you do not wish to do so,
* delete this exception statement from your version. If you delete this
* exception statement from all source files in the program, then also delete
* it in the license file.
*/
#define MONGO_LOG_DEFAULT_COMPONENT ::mongo::logger::LogComponent::kSharding
#include "mongo/platform/basic.h"
#include "mongo/db/s/split_chunk.h"
#include "mongo/base/status_with.h"
#include "mongo/bson/util/bson_extract.h"
#include "mongo/db/catalog/index_catalog.h"
#include "mongo/db/commands.h"
#include "mongo/db/db_raii.h"
#include "mongo/db/dbhelpers.h"
#include "mongo/db/index/index_descriptor.h"
#include "mongo/db/keypattern.h"
#include "mongo/db/namespace_string.h"
#include "mongo/db/query/internal_plans.h"
#include "mongo/db/s/collection_metadata.h"
#include "mongo/db/s/collection_sharding_state.h"
#include "mongo/db/s/sharding_state.h"
#include "mongo/s/catalog/type_chunk.h"
#include "mongo/s/client/shard_registry.h"
#include "mongo/s/grid.h"
#include "mongo/s/request_types/split_chunk_request_type.h"
#include "mongo/util/log.h"
namespace mongo {
namespace {
const ReadPreferenceSetting kPrimaryOnlyReadPreference{ReadPreference::PrimaryOnly};
bool checkIfSingleDoc(OperationContext* opCtx,
Collection* collection,
const IndexDescriptor* idx,
const ChunkType* chunk) {
KeyPattern kp(idx->keyPattern());
BSONObj newmin = Helpers::toKeyFormat(kp.extendRangeBound(chunk->getMin(), false));
BSONObj newmax = Helpers::toKeyFormat(kp.extendRangeBound(chunk->getMax(), true));
auto exec = InternalPlanner::indexScan(opCtx,
collection,
idx,
newmin,
newmax,
BoundInclusion::kIncludeStartKeyOnly,
PlanExecutor::NO_YIELD);
// check if exactly one document found
PlanExecutor::ExecState state;
BSONObj obj;
if (PlanExecutor::ADVANCED == (state = exec->getNext(&obj, NULL))) {
if (PlanExecutor::IS_EOF == (state = exec->getNext(&obj, NULL))) {
return true;
}
}
// Non-yielding collection scans from InternalPlanner will never error.
invariant(PlanExecutor::ADVANCED == state || PlanExecutor::IS_EOF == state);
return false;
}
/**
* Checks the collection's metadata for a successful split on the specified chunkRange using the
* specified splitKeys. Returns false if the metadata's chunks don't match the new chunk
* boundaries exactly.
*/
bool checkMetadataForSuccessfulSplitChunk(OperationContext* opCtx,
const NamespaceString& nss,
const ChunkRange& chunkRange,
const std::vector<BSONObj>& splitKeys) {
ScopedCollectionMetadata metadataAfterSplit;
{
AutoGetCollection autoColl(opCtx, nss, MODE_IS);
// Get collection metadata
metadataAfterSplit = CollectionShardingState::get(opCtx, nss.ns())->getMetadata();
}
auto newChunkBounds(splitKeys);
auto startKey = chunkRange.getMin();
newChunkBounds.push_back(chunkRange.getMax());
ChunkType nextChunk;
for (const auto& endKey : newChunkBounds) {
// Check that all new chunks fit the new chunk boundaries
if (!metadataAfterSplit->getNextChunk(startKey, &nextChunk) ||
nextChunk.getMax().woCompare(endKey)) {
return false;
}
startKey = endKey;
}
return true;
}
} // anonymous namespace
StatusWith<boost::optional<ChunkRange>> splitChunk(OperationContext* opCtx,
const NamespaceString& nss,
const BSONObj& keyPatternObj,
const ChunkRange& chunkRange,
const std::vector<BSONObj>& splitKeys,
const std::string& shardName,
const OID& expectedCollectionEpoch) {
ShardingState* shardingState = ShardingState::get(opCtx);
std::string errmsg;
const BSONObj min = chunkRange.getMin();
const BSONObj max = chunkRange.getMax();
//
// Lock the collection's metadata and get highest version for the current shard
// TODO(SERVER-25086): Remove distLock acquisition from split chunk
//
const std::string whyMessage(
str::stream() << "splitting chunk [" << min << ", " << max << ") in " << nss.toString());
auto scopedDistLock = Grid::get(opCtx)->catalogClient()->getDistLockManager()->lock(
opCtx, nss.ns(), whyMessage, DistLockManager::kSingleLockAttemptTimeout);
if (!scopedDistLock.isOK()) {
errmsg = str::stream() << "could not acquire collection lock for " << nss.toString()
<< " to split chunk [" << redact(min) << "," << redact(max) << ") "
<< causedBy(redact(scopedDistLock.getStatus()));
warning() << errmsg;
return scopedDistLock.getStatus();
}
// Always check our version remotely
ChunkVersion shardVersion;
Status refreshStatus = shardingState->refreshMetadataNow(opCtx, nss, &shardVersion);
if (!refreshStatus.isOK()) {
errmsg = str::stream() << "splitChunk cannot split chunk "
<< "[" << redact(min) << "," << redact(max) << ") "
<< causedBy(redact(refreshStatus));
warning() << errmsg;
return refreshStatus;
}
if (shardVersion.majorVersion() == 0) {
// It makes no sense to split if our version is zero and we have no chunks
errmsg = str::stream() << "splitChunk cannot split chunk "
<< "[" << redact(min) << "," << redact(max) << ") "
<< " with zero shard version";
warning() << errmsg;
return {ErrorCodes::CannotSplit, errmsg};
}
// Even though the splitChunk command transmits a value in the operation's shardVersion
// field, this value does not actually contain the shard version, but the global collection
// version.
if (expectedCollectionEpoch != shardVersion.epoch()) {
std::string msg = str::stream() << "splitChunk cannot split chunk "
<< "[" << redact(min) << "," << redact(max) << "), "
<< "collection '" << nss.ns() << "' may have been dropped. "
<< "current epoch: " << shardVersion.epoch()
<< ", cmd epoch: " << expectedCollectionEpoch;
warning() << msg;
return {ErrorCodes::StaleEpoch, msg};
}
ScopedCollectionMetadata collMetadata;
{
AutoGetCollection autoColl(opCtx, nss, MODE_IS);
// Get collection metadata
collMetadata = CollectionShardingState::get(opCtx, nss.ns())->getMetadata();
}
// With nonzero shard version, we must have metadata
invariant(collMetadata);
KeyPattern shardKeyPattern(collMetadata->getKeyPattern());
// If the shard uses a hashed key, then we must make sure that the split point is of
// type NumberLong.
if (KeyPattern::isHashedKeyPattern(shardKeyPattern.toBSON())) {
for (BSONObj splitKey : splitKeys) {
BSONObjIterator it(splitKey);
while (it.more()) {
BSONElement splitKeyElement = it.next();
if (splitKeyElement.type() != NumberLong) {
errmsg = str::stream() << "splitChunk cannot split chunk [" << redact(min)
<< "," << redact(max) << "), split point "
<< splitKeyElement.toString()
<< " must be of type "
"NumberLong for hashed shard key patterns";
warning() << errmsg;
return {ErrorCodes::CannotSplit, errmsg};
}
}
}
}
ChunkVersion collVersion = collMetadata->getCollVersion();
// With nonzero shard version, we must have a coll version >= our shard version
invariant(collVersion >= shardVersion);
{
ChunkType chunkToMove;
chunkToMove.setMin(min);
chunkToMove.setMax(max);
uassertStatusOK(collMetadata->checkChunkIsValid(chunkToMove));
}
// Commit the split to the config server.
auto request =
SplitChunkRequest(nss, shardName, expectedCollectionEpoch, chunkRange, splitKeys);
auto configCmdObj =
request.toConfigCommandBSON(ShardingCatalogClient::kMajorityWriteConcern.toBSON());
auto cmdResponseStatus =
Grid::get(opCtx)->shardRegistry()->getConfigShard()->runCommandWithFixedRetryAttempts(
opCtx,
kPrimaryOnlyReadPreference,
"admin",
configCmdObj,
Shard::RetryPolicy::kIdempotent);
//
// Refresh chunk metadata regardless of whether or not the split succeeded
//
{
ChunkVersion unusedShardVersion;
refreshStatus = shardingState->refreshMetadataNow(opCtx, nss, &unusedShardVersion);
if (!refreshStatus.isOK()) {
errmsg = str::stream() << "failed to refresh metadata for split chunk [" << redact(min)
<< "," << redact(max) << ") " << causedBy(redact(refreshStatus));
warning() << errmsg;
return refreshStatus;
}
}
// If we failed to get any response from the config server at all, despite retries, then we
// should just go ahead and fail the whole operation.
if (!cmdResponseStatus.isOK()) {
return cmdResponseStatus.getStatus();
}
// Check commandStatus and writeConcernStatus
auto commandStatus = cmdResponseStatus.getValue().commandStatus;
auto writeConcernStatus = cmdResponseStatus.getValue().writeConcernStatus;
// Send stale epoch if epoch of request did not match epoch of collection
if (commandStatus == ErrorCodes::StaleEpoch) {
std::string msg = str::stream() << "splitChunk cannot split chunk "
<< "[" << redact(min) << "," << redact(max) << "), "
<< "collection '" << nss.ns() << "' may have been dropped. "
<< "current epoch: " << collVersion.epoch()
<< ", cmd epoch: " << expectedCollectionEpoch;
warning() << msg;
return {commandStatus.code(), str::stream() << msg << redact(causedBy(commandStatus))};
}
//
// If _configsvrCommitChunkSplit returned an error, look at this shard's metadata to
// determine if the split actually did happen. This can happen if there's a network error
// getting the response from the first call to _configsvrCommitChunkSplit, but it actually
// succeeds, thus the automatic retry fails with a precondition violation, for example.
//
if ((!commandStatus.isOK() || !writeConcernStatus.isOK()) &&
checkMetadataForSuccessfulSplitChunk(opCtx, nss, chunkRange, splitKeys)) {
LOG(1) << "splitChunk [" << redact(min) << "," << redact(max)
<< ") has already been committed.";
} else if (!commandStatus.isOK()) {
return commandStatus;
} else if (!writeConcernStatus.isOK()) {
return writeConcernStatus;
}
AutoGetCollection autoColl(opCtx, nss, MODE_IS);
Collection* const collection = autoColl.getCollection();
if (!collection) {
warning() << "will not perform top-chunk checking since " << nss.toString()
<< " does not exist after splitting";
return boost::optional<ChunkRange>(boost::none);
}
// Allow multiKey based on the invariant that shard keys must be single-valued. Therefore,
// any multi-key index prefixed by shard key cannot be multikey over the shard key fields.
IndexDescriptor* idx =
collection->getIndexCatalog()->findShardKeyPrefixedIndex(opCtx, keyPatternObj, false);
if (!idx) {
return boost::optional<ChunkRange>(boost::none);
}
auto backChunk = ChunkType();
backChunk.setMin(splitKeys.back());
backChunk.setMax(max);
auto frontChunk = ChunkType();
frontChunk.setMin(min);
frontChunk.setMax(splitKeys.front());
if (shardKeyPattern.globalMax().woCompare(backChunk.getMax()) == 0 &&
checkIfSingleDoc(opCtx, collection, idx, &backChunk)) {
return boost::optional<ChunkRange>(ChunkRange(backChunk.getMin(), backChunk.getMax()));
} else if (shardKeyPattern.globalMin().woCompare(frontChunk.getMin()) == 0 &&
checkIfSingleDoc(opCtx, collection, idx, &frontChunk)) {
return boost::optional<ChunkRange>(ChunkRange(frontChunk.getMin(), frontChunk.getMax()));
}
return boost::optional<ChunkRange>(boost::none);
}
} // namespace mongo
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