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rocksdb/db/merge_helper.cc

225 lines
8.9 KiB

// Copyright (c) 2013, Facebook, Inc. All rights reserved.
// This source code is licensed under the BSD-style license found in the
// LICENSE file in the root directory of this source tree. An additional grant
// of patent rights can be found in the PATENTS file in the same directory.
#include "db/merge_helper.h"
#include <stdio.h>
#include <string>
#include "db/dbformat.h"
#include "rocksdb/comparator.h"
#include "rocksdb/db.h"
#include "rocksdb/merge_operator.h"
#include "util/perf_context_imp.h"
#include "util/statistics.h"
#include "util/stop_watch.h"
namespace rocksdb {
// TODO(agiardullo): Clean up merge callsites to use this func
Status MergeHelper::TimedFullMerge(const Slice& key, const Slice* value,
const std::deque<std::string>& operands,
const MergeOperator* merge_operator,
Statistics* statistics, Env* env,
Logger* logger, std::string* result) {
if (operands.size() == 0) {
result->assign(value->data(), value->size());
return Status::OK();
}
if (merge_operator == nullptr) {
return Status::NotSupported("Provide a merge_operator when opening DB");
}
// Setup to time the merge
StopWatchNano timer(env, statistics != nullptr);
PERF_TIMER_GUARD(merge_operator_time_nanos);
// Do the merge
bool success =
merge_operator->FullMerge(key, value, operands, result, logger);
RecordTick(statistics, MERGE_OPERATION_TOTAL_TIME,
env != nullptr ? timer.ElapsedNanos() : 0);
if (!success) {
RecordTick(statistics, NUMBER_MERGE_FAILURES);
return Status::Corruption("Error: Could not perform merge.");
}
return Status::OK();
}
// PRE: iter points to the first merge type entry
// POST: iter points to the first entry beyond the merge process (or the end)
// keys_, operands_ are updated to reflect the merge result.
// keys_ stores the list of keys encountered while merging.
// operands_ stores the list of merge operands encountered while merging.
// keys_[i] corresponds to operands_[i] for each i.
Status MergeHelper::MergeUntil(Iterator* iter, const SequenceNumber stop_before,
const bool at_bottom, Statistics* stats,
Env* env_) {
// Get a copy of the internal key, before it's invalidated by iter->Next()
// Also maintain the list of merge operands seen.
assert(HasOperator());
keys_.clear();
operands_.clear();
keys_.push_front(iter->key().ToString());
operands_.push_front(iter->value().ToString());
assert(user_merge_operator_);
// We need to parse the internal key again as the parsed key is
// backed by the internal key!
// Assume no internal key corruption as it has been successfully parsed
// by the caller.
// Invariant: keys_.back() will not change. Hence, orig_ikey is always valid.
ParsedInternalKey orig_ikey;
ParseInternalKey(keys_.back(), &orig_ikey);
Status s;
bool hit_the_next_user_key = false;
for (iter->Next(); iter->Valid(); iter->Next()) {
ParsedInternalKey ikey;
assert(operands_.size() >= 1); // Should be invariants!
assert(keys_.size() == operands_.size());
if (!ParseInternalKey(iter->key(), &ikey)) {
// stop at corrupted key
if (assert_valid_internal_key_) {
assert(!"corrupted internal key is not expected");
}
break;
} else if (!user_comparator_->Equal(ikey.user_key, orig_ikey.user_key)) {
// hit a different user key, stop right here
hit_the_next_user_key = true;
break;
} else if (stop_before && ikey.sequence <= stop_before) {
// hit an entry that's visible by the previous snapshot, can't touch that
break;
}
// At this point we are guaranteed that we need to process this key.
assert(ikey.type <= kValueTypeForSeek);
if (ikey.type != kTypeMerge) {
// hit a put/delete
// => merge the put value or a nullptr with operands_
// => store result in operands_.back() (and update keys_.back())
// => change the entry type to kTypeValue for keys_.back()
// We are done! Success!
//
// TODO(noetzli) If the merge operator returns false, we are currently
// (almost) silently dropping the put/delete. That's probably not what we
// want.
const Slice val = iter->value();
const Slice* val_ptr = (kTypeValue == ikey.type) ? &val : nullptr;
std::string merge_result;
s = TimedFullMerge(ikey.user_key, val_ptr, operands_,
user_merge_operator_, stats, env_, logger_,
&merge_result);
// We store the result in keys_.back() and operands_.back()
// if nothing went wrong (i.e.: no operand corruption on disk)
if (s.ok()) {
// The original key encountered
std::string original_key = std::move(keys_.back());
orig_ikey.type = kTypeValue;
UpdateInternalKey(&original_key, orig_ikey.sequence, orig_ikey.type);
keys_.clear();
operands_.clear();
keys_.emplace_front(std::move(original_key));
operands_.emplace_front(std::move(merge_result));
}
// move iter to the next entry
iter->Next();
return s;
} else {
// hit a merge
// => merge the operand into the front of the operands_ list
// => use the user's associative merge function to determine how.
// => then continue because we haven't yet seen a Put/Delete.
assert(!operands_.empty()); // Should have at least one element in it
// keep queuing keys and operands until we either meet a put / delete
// request or later did a partial merge.
keys_.push_front(iter->key().ToString());
operands_.push_front(iter->value().ToString());
}
}
// We are sure we have seen this key's entire history if we are at the
// last level and exhausted all internal keys of this user key.
// NOTE: !iter->Valid() does not necessarily mean we hit the
// beginning of a user key, as versions of a user key might be
// split into multiple files (even files on the same level)
// and some files might not be included in the compaction/merge.
//
// There are also cases where we have seen the root of history of this
// key without being sure of it. Then, we simply miss the opportunity
// to combine the keys. Since VersionSet::SetupOtherInputs() always makes
// sure that all merge-operands on the same level get compacted together,
// this will simply lead to these merge operands moving to the next level.
//
// So, we only perform the following logic (to merge all operands together
// without a Put/Delete) if we are certain that we have seen the end of key.
bool surely_seen_the_beginning = hit_the_next_user_key && at_bottom;
if (surely_seen_the_beginning) {
// do a final merge with nullptr as the existing value and say
// bye to the merge type (it's now converted to a Put)
assert(kTypeMerge == orig_ikey.type);
assert(operands_.size() >= 1);
assert(operands_.size() == keys_.size());
std::string merge_result;
s = TimedFullMerge(orig_ikey.user_key, nullptr, operands_,
user_merge_operator_, stats, env_, logger_,
&merge_result);
if (s.ok()) {
// The original key encountered
std::string original_key = std::move(keys_.back());
orig_ikey.type = kTypeValue;
UpdateInternalKey(&original_key, orig_ikey.sequence, orig_ikey.type);
keys_.clear();
operands_.clear();
keys_.emplace_front(std::move(original_key));
operands_.emplace_front(std::move(merge_result));
}
} else {
// We haven't seen the beginning of the key nor a Put/Delete.
// Attempt to use the user's associative merge function to
// merge the stacked merge operands into a single operand.
//
// TODO(noetzli) The docblock of MergeUntil suggests that a successful
// partial merge returns Status::OK(). Should we change the status code
// after a successful partial merge?
s = Status::MergeInProgress();
if (operands_.size() >= 2 &&
operands_.size() >= min_partial_merge_operands_) {
bool merge_success = false;
std::string merge_result;
{
StopWatchNano timer(env_, stats != nullptr);
PERF_TIMER_GUARD(merge_operator_time_nanos);
merge_success = user_merge_operator_->PartialMergeMulti(
orig_ikey.user_key,
std::deque<Slice>(operands_.begin(), operands_.end()),
&merge_result, logger_);
RecordTick(stats, MERGE_OPERATION_TOTAL_TIME,
env_ != nullptr ? timer.ElapsedNanos() : 0);
}
if (merge_success) {
// Merging of operands (associative merge) was successful.
// Replace operands with the merge result
operands_.clear();
operands_.emplace_front(std::move(merge_result));
keys_.erase(keys_.begin(), keys_.end() - 1);
}
}
}
return s;
}
} // namespace rocksdb