rocksdb/db/merge_helper.cc
Mike Kolupaev 247d0979aa Support for range skips in compaction filter
Summary:
This adds the ability for compaction filter to say "drop this key-value, and also drop everything up to key x". This will cause the compaction to seek input iterator to x, without reading the data. This can make compaction much faster when large consecutive chunks of data are filtered out. See the changes in include/rocksdb/compaction_filter.h for the new API.

Along the way this diff also adds ability for compaction filter changing merge operands, similar to how it can change values; we're not going to use this feature, it just seemed easier and cleaner to implement it than to document that it's not implemented :)

The diff is not as big as it may seem, about half of the lines are a test.
Closes https://github.com/facebook/rocksdb/pull/1599

Differential Revision: D4252092

Pulled By: al13n321

fbshipit-source-id: 41e1e48
2016-12-01 07:09:15 -08:00

359 lines
14 KiB
C++

// Copyright (c) 2011-present, 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 "table/internal_iterator.h"
#include "util/perf_context_imp.h"
#include "util/statistics.h"
namespace rocksdb {
Status MergeHelper::TimedFullMerge(const MergeOperator* merge_operator,
const Slice& key, const Slice* value,
const std::vector<Slice>& operands,
std::string* result, Logger* logger,
Statistics* statistics, Env* env,
Slice* result_operand) {
assert(merge_operator != nullptr);
if (operands.size() == 0) {
assert(value != nullptr && result != nullptr);
result->assign(value->data(), value->size());
return Status::OK();
}
bool success;
Slice tmp_result_operand(nullptr, 0);
const MergeOperator::MergeOperationInput merge_in(key, value, operands,
logger);
MergeOperator::MergeOperationOutput merge_out(*result, tmp_result_operand);
{
// Setup to time the merge
StopWatchNano timer(env, statistics != nullptr);
PERF_TIMER_GUARD(merge_operator_time_nanos);
// Do the merge
success = merge_operator->FullMergeV2(merge_in, &merge_out);
if (tmp_result_operand.data()) {
// FullMergeV2 result is an existing operand
if (result_operand != nullptr) {
*result_operand = tmp_result_operand;
} else {
result->assign(tmp_result_operand.data(), tmp_result_operand.size());
}
} else if (result_operand) {
*result_operand = Slice(nullptr, 0);
}
RecordTick(statistics, MERGE_OPERATION_TOTAL_TIME,
statistics ? 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(InternalIterator* iter,
RangeDelAggregator* range_del_agg,
const SequenceNumber stop_before,
const bool at_bottom) {
// 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();
merge_context_.Clear();
has_compaction_filter_skip_until_ = false;
assert(user_merge_operator_);
bool first_key = true;
// 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.
// original_key_is_iter variable is just caching the information:
// original_key_is_iter == (iter->key().ToString() == original_key)
bool original_key_is_iter = true;
std::string original_key = iter->key().ToString();
// Important:
// orig_ikey is backed by original_key if keys_.empty()
// orig_ikey is backed by keys_.back() if !keys_.empty()
ParsedInternalKey orig_ikey;
ParseInternalKey(original_key, &orig_ikey);
Status s;
bool hit_the_next_user_key = false;
for (; iter->Valid(); iter->Next(), original_key_is_iter = false) {
ParsedInternalKey ikey;
assert(keys_.size() == merge_context_.GetNumOperands());
if (!ParseInternalKey(iter->key(), &ikey)) {
// stop at corrupted key
if (assert_valid_internal_key_) {
assert(!"Corrupted internal key not expected.");
return Status::Corruption("Corrupted internal key not expected.");
}
break;
} else if (first_key) {
assert(user_comparator_->Equal(ikey.user_key, orig_ikey.user_key));
first_key = false;
} 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(IsValueType(ikey.type));
if (ikey.type != kTypeMerge) {
// hit a put/delete/single 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!
// If there are no operands, just return the Status::OK(). That will cause
// the compaction iterator to write out the key we're currently at, which
// is the put/delete we just encountered.
if (keys_.empty()) {
return Status::OK();
}
// TODO(noetzli) If the merge operator returns false, we are currently
// (almost) silently dropping the put/delete. That's probably not what we
// want. Also if we're in compaction and it's a put, it would be nice to
// run compaction filter on it.
const Slice val = iter->value();
const Slice* val_ptr = (kTypeValue == ikey.type) ? &val : nullptr;
std::string merge_result;
s = TimedFullMerge(user_merge_operator_, ikey.user_key, val_ptr,
merge_context_.GetOperands(), &merge_result, logger_,
stats_, env_);
// 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
original_key = std::move(keys_.back());
orig_ikey.type = kTypeValue;
UpdateInternalKey(&original_key, orig_ikey.sequence, orig_ikey.type);
keys_.clear();
merge_context_.Clear();
keys_.emplace_front(std::move(original_key));
merge_context_.PushOperand(merge_result);
}
// move iter to the next entry
iter->Next();
return s;
} else {
// hit a merge
// => if there is a compaction filter, apply it.
// => check for range tombstones covering the operand
// => merge the operand into the front of the operands_ list
// if not filtered
// => then continue because we haven't yet seen a Put/Delete.
//
// Keep queuing keys and operands until we either meet a put / delete
// request or later did a partial merge.
Slice value_slice = iter->value();
// add an operand to the list if:
// 1) it's included in one of the snapshots. in that case we *must* write
// it out, no matter what compaction filter says
// 2) it's not filtered by a compaction filter
CompactionFilter::Decision filter =
ikey.sequence <= latest_snapshot_
? CompactionFilter::Decision::kKeep
: FilterMerge(orig_ikey.user_key, value_slice);
if (range_del_agg != nullptr &&
range_del_agg->ShouldDelete(iter->key()) &&
filter != CompactionFilter::Decision::kRemoveAndSkipUntil) {
filter = CompactionFilter::Decision::kRemove;
}
if (filter == CompactionFilter::Decision::kKeep ||
filter == CompactionFilter::Decision::kChangeValue) {
if (original_key_is_iter) {
// this is just an optimization that saves us one memcpy
keys_.push_front(std::move(original_key));
} else {
keys_.push_front(iter->key().ToString());
}
if (keys_.size() == 1) {
// we need to re-anchor the orig_ikey because it was anchored by
// original_key before
ParseInternalKey(keys_.back(), &orig_ikey);
}
if (filter == CompactionFilter::Decision::kKeep) {
merge_context_.PushOperand(
value_slice, iter->IsValuePinned() /* operand_pinned */);
} else { // kChangeValue
// Compaction filter asked us to change the operand from value_slice
// to compaction_filter_value_.
merge_context_.PushOperand(compaction_filter_value_, false);
}
} else if (filter == CompactionFilter::Decision::kRemoveAndSkipUntil) {
// Compaction filter asked us to remove this key altogether
// (not just this operand), along with some keys following it.
keys_.clear();
merge_context_.Clear();
has_compaction_filter_skip_until_ = true;
return Status::OK();
}
}
}
if (merge_context_.GetNumOperands() == 0) {
// we filtered out all the merge operands
return Status::OK();
}
// 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(merge_context_.GetNumOperands() >= 1);
assert(merge_context_.GetNumOperands() == keys_.size());
std::string merge_result;
s = TimedFullMerge(user_merge_operator_, orig_ikey.user_key, nullptr,
merge_context_.GetOperands(), &merge_result, logger_,
stats_, env_);
if (s.ok()) {
// The original key encountered
// We are certain that keys_ is not empty here (see assertions couple of
// lines before).
original_key = std::move(keys_.back());
orig_ikey.type = kTypeValue;
UpdateInternalKey(&original_key, orig_ikey.sequence, orig_ikey.type);
keys_.clear();
merge_context_.Clear();
keys_.emplace_front(std::move(original_key));
merge_context_.PushOperand(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 (merge_context_.GetNumOperands() >= 2 &&
merge_context_.GetNumOperands() >= 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>(merge_context_.GetOperands().begin(),
merge_context_.GetOperands().end()),
&merge_result, logger_);
RecordTick(stats_, MERGE_OPERATION_TOTAL_TIME,
stats_ ? timer.ElapsedNanosSafe() : 0);
}
if (merge_success) {
// Merging of operands (associative merge) was successful.
// Replace operands with the merge result
merge_context_.Clear();
merge_context_.PushOperand(merge_result);
keys_.erase(keys_.begin(), keys_.end() - 1);
}
}
}
return s;
}
MergeOutputIterator::MergeOutputIterator(const MergeHelper* merge_helper)
: merge_helper_(merge_helper) {
it_keys_ = merge_helper_->keys().rend();
it_values_ = merge_helper_->values().rend();
}
void MergeOutputIterator::SeekToFirst() {
const auto& keys = merge_helper_->keys();
const auto& values = merge_helper_->values();
assert(keys.size() == values.size());
it_keys_ = keys.rbegin();
it_values_ = values.rbegin();
}
void MergeOutputIterator::Next() {
++it_keys_;
++it_values_;
}
CompactionFilter::Decision MergeHelper::FilterMerge(const Slice& user_key,
const Slice& value_slice) {
if (compaction_filter_ == nullptr) {
return CompactionFilter::Decision::kKeep;
}
if (stats_ != nullptr) {
filter_timer_.Start();
}
compaction_filter_value_.clear();
compaction_filter_skip_until_.Clear();
auto ret = compaction_filter_->FilterV2(
level_, user_key, CompactionFilter::ValueType::kMergeOperand, value_slice,
&compaction_filter_value_, compaction_filter_skip_until_.rep());
if (ret == CompactionFilter::Decision::kRemoveAndSkipUntil) {
if (user_comparator_->Compare(*compaction_filter_skip_until_.rep(),
user_key) <= 0) {
// Invalid skip_until returned from compaction filter.
// Keep the key as per FilterV2 documentation.
ret = CompactionFilter::Decision::kKeep;
} else {
compaction_filter_skip_until_.ConvertFromUserKey(kMaxSequenceNumber,
kValueTypeForSeek);
}
}
total_filter_time_ += filter_timer_.ElapsedNanosSafe();
return ret;
}
} // namespace rocksdb