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/**
* Copyright (C) 2016 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 <algorithm>
#include <string>
#include <vector>
#include "mongo/bson/simple_bsonobj_comparator.h"
#include "mongo/db/auth/action_set.h"
#include "mongo/db/auth/action_type.h"
#include "mongo/db/auth/authorization_manager.h"
#include "mongo/db/auth/authorization_session.h"
#include "mongo/db/auth/privilege.h"
#include "mongo/db/bson/dotted_path_support.h"
#include "mongo/db/catalog/collection.h"
#include "mongo/db/commands.h"
#include "mongo/db/db_raii.h"
#include "mongo/db/dbhelpers.h"
#include "mongo/db/exec/working_set_common.h"
#include "mongo/db/index/index_descriptor.h"
#include "mongo/db/keypattern.h"
#include "mongo/db/query/internal_plans.h"
#include "mongo/s/catalog/type_chunk.h"
#include "mongo/s/chunk.h"
#include "mongo/util/log.h"
#include "mongo/util/timer.h"
namespace mongo {
using std::unique_ptr;
using std::set;
using std::string;
using std::stringstream;
using std::vector;
namespace {
const int kMaxObjectPerChunk{250000};
BSONObj prettyKey(const BSONObj& keyPattern, const BSONObj& key) {
return key.replaceFieldNames(keyPattern).clientReadable();
}
class SplitVector : public Command {
public:
SplitVector() : Command("splitVector", false) {}
bool supportsWriteConcern(const BSONObj& cmd) const override {
return false;
}
bool slaveOk() const override {
return false;
}
void help(stringstream& help) const override {
help << "Internal command.\n"
"examples:\n"
" { splitVector : \"blog.post\" , keyPattern:{x:1} , min:{x:10} , max:{x:20}, "
"maxChunkSize:200 }\n"
" maxChunkSize unit in MBs\n"
" May optionally specify 'maxSplitPoints' and 'maxChunkObjects' to avoid "
"traversing the whole chunk\n"
" \n"
" { splitVector : \"blog.post\" , keyPattern:{x:1} , min:{x:10} , max:{x:20}, "
"force: true }\n"
" 'force' will produce one split point even if data is small; defaults to false\n"
"NOTE: This command may take a while to run";
}
Status checkAuthForCommand(Client* client,
const std::string& dbname,
const BSONObj& cmdObj) override {
if (!AuthorizationSession::get(client)->isAuthorizedForActionsOnResource(
ResourcePattern::forExactNamespace(NamespaceString(parseNs(dbname, cmdObj))),
ActionType::splitVector)) {
return Status(ErrorCodes::Unauthorized, "Unauthorized");
}
return Status::OK();
}
std::string parseNs(const string& dbname, const BSONObj& cmdObj) const override {
return parseNsFullyQualified(dbname, cmdObj);
}
bool run(OperationContext* opCtx,
const string& dbname,
BSONObj& jsobj,
int options,
string& errmsg,
BSONObjBuilder& result) override {
//
// 1.a We'll parse the parameters in two steps. First, make sure the we can use the split
// index to get a good approximation of the size of the chunk -- without needing to
// access the actual data.
//
const NamespaceString nss = NamespaceString(parseNs(dbname, jsobj));
BSONObj keyPattern = jsobj.getObjectField("keyPattern");
if (keyPattern.isEmpty()) {
errmsg = "no key pattern found in splitVector";
return false;
}
// If min and max are not provided use the "minKey" and "maxKey" for the sharding key
// pattern.
BSONObj min = jsobj.getObjectField("min");
BSONObj max = jsobj.getObjectField("max");
if (min.isEmpty() != max.isEmpty()) {
errmsg = "either provide both min and max or leave both empty";
return false;
}
long long maxSplitPoints = 0;
BSONElement maxSplitPointsElem = jsobj["maxSplitPoints"];
if (maxSplitPointsElem.isNumber()) {
maxSplitPoints = maxSplitPointsElem.numberLong();
}
long long maxChunkObjects = kMaxObjectPerChunk;
BSONElement MaxChunkObjectsElem = jsobj["maxChunkObjects"];
if (MaxChunkObjectsElem.isNumber()) {
maxChunkObjects = MaxChunkObjectsElem.numberLong();
}
vector<BSONObj> splitKeys;
{
// Get the size estimate for this namespace
AutoGetCollection autoColl(opCtx, nss, MODE_IS);
Collection* const collection = autoColl.getCollection();
if (!collection) {
errmsg = "ns not found";
return false;
}
// 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, keyPattern, false);
if (idx == NULL) {
errmsg = (string) "couldn't find index over splitting key " +
keyPattern.clientReadable().toString();
return false;
}
// extend min to get (min, MinKey, MinKey, ....)
KeyPattern kp(idx->keyPattern());
min = Helpers::toKeyFormat(kp.extendRangeBound(min, false));
if (max.isEmpty()) {
// if max not specified, make it (MaxKey, Maxkey, MaxKey...)
max = Helpers::toKeyFormat(kp.extendRangeBound(max, true));
} else {
// otherwise make it (max,MinKey,MinKey...) so that bound is non-inclusive
max = Helpers::toKeyFormat(kp.extendRangeBound(max, false));
}
const long long recCount = collection->numRecords(opCtx);
const long long dataSize = collection->dataSize(opCtx);
//
// 1.b Now that we have the size estimate, go over the remaining parameters and apply
// any maximum size restrictions specified there.
//
// 'force'-ing a split is equivalent to having maxChunkSize be the size of the current
// chunk, i.e., the logic below will split that chunk in half
long long maxChunkSize = 0;
bool forceMedianSplit = false;
{
BSONElement maxSizeElem = jsobj["maxChunkSize"];
BSONElement forceElem = jsobj["force"];
if (forceElem.trueValue()) {
forceMedianSplit = true;
// This chunk size is effectively ignored if force is true
maxChunkSize = dataSize;
} else if (maxSizeElem.isNumber()) {
maxChunkSize = maxSizeElem.numberLong() * 1 << 20;
} else {
maxSizeElem = jsobj["maxChunkSizeBytes"];
if (maxSizeElem.isNumber()) {
maxChunkSize = maxSizeElem.numberLong();
}
}
// We need a maximum size for the chunk, unless we're not actually capable of
// finding any split points.
if (maxChunkSize <= 0 && recCount != 0) {
errmsg =
"need to specify the desired max chunk size (maxChunkSize or "
"maxChunkSizeBytes)";
return false;
}
}
// If there's not enough data for more than one chunk, no point continuing.
if (dataSize < maxChunkSize || recCount == 0) {
vector<BSONObj> emptyVector;
result.append("splitKeys", emptyVector);
return true;
}
log() << "request split points lookup for chunk " << nss.toString() << " "
<< redact(min) << " -->> " << redact(max);
// We'll use the average object size and number of object to find approximately how many
// keys each chunk should have. We'll split at half the maxChunkSize or maxChunkObjects,
// if provided.
const long long avgRecSize = dataSize / recCount;
long long keyCount = maxChunkSize / (2 * avgRecSize);
if (maxChunkObjects && (maxChunkObjects < keyCount)) {
log() << "limiting split vector to " << maxChunkObjects << " (from " << keyCount
<< ") objects ";
keyCount = maxChunkObjects;
}
//
// 2. Traverse the index and add the keyCount-th key to the result vector. If that key
// appeared in the vector before, we omit it. The invariant here is that all the
// instances of a given key value live in the same chunk.
//
Timer timer;
long long currCount = 0;
long long numChunks = 0;
unique_ptr<PlanExecutor> exec(
InternalPlanner::indexScan(opCtx,
collection,
idx,
min,
max,
BoundInclusion::kIncludeStartKeyOnly,
PlanExecutor::YIELD_MANUAL,
InternalPlanner::FORWARD));
BSONObj currKey;
PlanExecutor::ExecState state = exec->getNext(&currKey, NULL);
if (PlanExecutor::ADVANCED != state) {
errmsg = "can't open a cursor for splitting (desired range is possibly empty)";
return false;
}
// Use every 'keyCount'-th key as a split point. We add the initial key as a sentinel,
// to be removed at the end. If a key appears more times than entries allowed on a
// chunk, we issue a warning and split on the following key.
auto tooFrequentKeys = SimpleBSONObjComparator::kInstance.makeBSONObjSet();
splitKeys.push_back(dotted_path_support::extractElementsBasedOnTemplate(
prettyKey(idx->keyPattern(), currKey.getOwned()), keyPattern));
exec->setYieldPolicy(PlanExecutor::YIELD_AUTO, collection);
while (1) {
while (PlanExecutor::ADVANCED == state) {
currCount++;
if (currCount > keyCount && !forceMedianSplit) {
currKey = dotted_path_support::extractElementsBasedOnTemplate(
prettyKey(idx->keyPattern(), currKey.getOwned()), keyPattern);
// Do not use this split key if it is the same used in the previous split
// point.
if (currKey.woCompare(splitKeys.back()) == 0) {
tooFrequentKeys.insert(currKey.getOwned());
} else {
splitKeys.push_back(currKey.getOwned());
currCount = 0;
numChunks++;
LOG(4) << "picked a split key: " << redact(currKey);
}
}
// Stop if we have enough split points.
if (maxSplitPoints && (numChunks >= maxSplitPoints)) {
log() << "max number of requested split points reached (" << numChunks
<< ") before the end of chunk " << nss.toString() << " "
<< redact(min) << " -->> " << redact(max);
break;
}
state = exec->getNext(&currKey, NULL);
}
if (PlanExecutor::DEAD == state || PlanExecutor::FAILURE == state) {
return appendCommandStatus(
result,
Status(ErrorCodes::OperationFailed,
str::stream() << "Executor error during splitVector command: "
<< WorkingSetCommon::toStatusString(currKey)));
}
if (!forceMedianSplit)
break;
//
// If we're forcing a split at the halfway point, then the first pass was just
// to count the keys, and we still need a second pass.
//
forceMedianSplit = false;
keyCount = currCount / 2;
currCount = 0;
log() << "splitVector doing another cycle because of force, keyCount now: "
<< keyCount;
exec = InternalPlanner::indexScan(opCtx,
collection,
idx,
min,
max,
BoundInclusion::kIncludeStartKeyOnly,
PlanExecutor::YIELD_MANUAL,
InternalPlanner::FORWARD);
exec->setYieldPolicy(PlanExecutor::YIELD_AUTO, collection);
state = exec->getNext(&currKey, NULL);
}
//
// 3. Format the result and issue any warnings about the data we gathered while
// traversing the index
//
// Warn for keys that are more numerous than maxChunkSize allows.
for (auto it = tooFrequentKeys.cbegin(); it != tooFrequentKeys.cend(); ++it) {
warning() << "possible low cardinality key detected in " << nss.toString()
<< " - key is " << prettyKey(idx->keyPattern(), *it);
}
// Remove the sentinel at the beginning before returning
splitKeys.erase(splitKeys.begin());
if (timer.millis() > serverGlobalParams.slowMS) {
warning() << "Finding the split vector for " << nss.toString() << " over "
<< redact(keyPattern) << " keyCount: " << keyCount
<< " numSplits: " << splitKeys.size() << " lookedAt: " << currCount
<< " took " << timer.millis() << "ms";
}
// Warning: we are sending back an array of keys but are currently limited to
// 4MB work of 'result' size. This should be okay for now.
result.append("timeMillis", timer.millis());
}
// Make sure splitKeys is in ascending order
std::sort(
splitKeys.begin(), splitKeys.end(), SimpleBSONObjComparator::kInstance.makeLessThan());
result.append("splitKeys", splitKeys);
return true;
}
} cmdSplitVector;
} // namespace
} // namespace mongo
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