01eabf7375
Summary: Both the single deletion and the value are included in compaction outputs, so no need to update the stat for the value's deletion yet, otherwise it'd be double-counted. Closes https://github.com/facebook/rocksdb/pull/1574 Differential Revision: D4241181 Pulled By: ajkr fbshipit-source-id: c9aaa15
474 lines
20 KiB
C++
474 lines
20 KiB
C++
// Use of this source code is governed by a BSD-style license that can be
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// found in the LICENSE file. See the AUTHORS file for names of contributors.
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// Copyright (c) 2011-present, Facebook, Inc. All rights reserved.
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// This source code is licensed under the BSD-style license found in the
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// LICENSE file in the root directory of this source tree. An additional grant
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// of patent rights can be found in the PATENTS file in the same directory.
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#include "db/compaction_iterator.h"
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#include "table/internal_iterator.h"
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namespace rocksdb {
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CompactionIterator::CompactionIterator(
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InternalIterator* input, const Comparator* cmp, MergeHelper* merge_helper,
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SequenceNumber last_sequence, std::vector<SequenceNumber>* snapshots,
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SequenceNumber earliest_write_conflict_snapshot, Env* env,
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bool expect_valid_internal_key, RangeDelAggregator* range_del_agg,
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const Compaction* compaction, const CompactionFilter* compaction_filter,
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LogBuffer* log_buffer)
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: input_(input),
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cmp_(cmp),
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merge_helper_(merge_helper),
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snapshots_(snapshots),
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earliest_write_conflict_snapshot_(earliest_write_conflict_snapshot),
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env_(env),
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expect_valid_internal_key_(expect_valid_internal_key),
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range_del_agg_(range_del_agg),
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compaction_(compaction),
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compaction_filter_(compaction_filter),
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log_buffer_(log_buffer),
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merge_out_iter_(merge_helper_) {
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assert(compaction_filter_ == nullptr || compaction_ != nullptr);
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bottommost_level_ =
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compaction_ == nullptr ? false : compaction_->bottommost_level();
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if (compaction_ != nullptr) {
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level_ptrs_ = std::vector<size_t>(compaction_->number_levels(), 0);
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}
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if (snapshots_->size() == 0) {
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// optimize for fast path if there are no snapshots
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visible_at_tip_ = true;
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earliest_snapshot_ = last_sequence;
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latest_snapshot_ = 0;
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} else {
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visible_at_tip_ = false;
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earliest_snapshot_ = snapshots_->at(0);
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latest_snapshot_ = snapshots_->back();
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}
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if (compaction_filter_ != nullptr && compaction_filter_->IgnoreSnapshots()) {
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ignore_snapshots_ = true;
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} else {
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ignore_snapshots_ = false;
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}
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input_->SetPinnedItersMgr(&pinned_iters_mgr_);
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}
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CompactionIterator::~CompactionIterator() {
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// input_ Iteartor lifetime is longer than pinned_iters_mgr_ lifetime
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input_->SetPinnedItersMgr(nullptr);
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}
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void CompactionIterator::ResetRecordCounts() {
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iter_stats_.num_record_drop_user = 0;
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iter_stats_.num_record_drop_hidden = 0;
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iter_stats_.num_record_drop_obsolete = 0;
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iter_stats_.num_record_drop_range_del = 0;
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iter_stats_.num_range_del_drop_obsolete = 0;
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}
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void CompactionIterator::SeekToFirst() {
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NextFromInput();
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PrepareOutput();
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}
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void CompactionIterator::Next() {
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// If there is a merge output, return it before continuing to process the
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// input.
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if (merge_out_iter_.Valid()) {
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merge_out_iter_.Next();
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// Check if we returned all records of the merge output.
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if (merge_out_iter_.Valid()) {
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key_ = merge_out_iter_.key();
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value_ = merge_out_iter_.value();
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bool valid_key __attribute__((__unused__)) =
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ParseInternalKey(key_, &ikey_);
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// MergeUntil stops when it encounters a corrupt key and does not
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// include them in the result, so we expect the keys here to be valid.
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assert(valid_key);
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// Keep current_key_ in sync.
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current_key_.UpdateInternalKey(ikey_.sequence, ikey_.type);
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key_ = current_key_.GetKey();
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ikey_.user_key = current_key_.GetUserKey();
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valid_ = true;
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} else {
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// We consumed all pinned merge operands, release pinned iterators
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pinned_iters_mgr_.ReleasePinnedData();
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// MergeHelper moves the iterator to the first record after the merged
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// records, so even though we reached the end of the merge output, we do
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// not want to advance the iterator.
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NextFromInput();
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}
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} else {
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// Only advance the input iterator if there is no merge output and the
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// iterator is not already at the next record.
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if (!at_next_) {
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input_->Next();
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}
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NextFromInput();
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}
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if (valid_) {
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// Record that we've ouputted a record for the current key.
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has_outputted_key_ = true;
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}
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PrepareOutput();
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}
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void CompactionIterator::NextFromInput() {
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at_next_ = false;
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valid_ = false;
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while (!valid_ && input_->Valid()) {
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key_ = input_->key();
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value_ = input_->value();
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iter_stats_.num_input_records++;
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if (!ParseInternalKey(key_, &ikey_)) {
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// If `expect_valid_internal_key_` is false, return the corrupted key
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// and let the caller decide what to do with it.
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// TODO(noetzli): We should have a more elegant solution for this.
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if (expect_valid_internal_key_) {
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assert(!"Corrupted internal key not expected.");
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status_ = Status::Corruption("Corrupted internal key not expected.");
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break;
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}
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key_ = current_key_.SetKey(key_);
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has_current_user_key_ = false;
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current_user_key_sequence_ = kMaxSequenceNumber;
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current_user_key_snapshot_ = 0;
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iter_stats_.num_input_corrupt_records++;
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valid_ = true;
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break;
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}
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// Update input statistics
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if (ikey_.type == kTypeDeletion || ikey_.type == kTypeSingleDeletion) {
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iter_stats_.num_input_deletion_records++;
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}
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iter_stats_.total_input_raw_key_bytes += key_.size();
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iter_stats_.total_input_raw_value_bytes += value_.size();
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// Check whether the user key changed. After this if statement current_key_
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// is a copy of the current input key (maybe converted to a delete by the
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// compaction filter). ikey_.user_key is pointing to the copy.
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if (!has_current_user_key_ ||
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!cmp_->Equal(ikey_.user_key, current_user_key_)) {
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// First occurrence of this user key
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// Copy key for output
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key_ = current_key_.SetKey(key_, &ikey_);
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current_user_key_ = ikey_.user_key;
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has_current_user_key_ = true;
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has_outputted_key_ = false;
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current_user_key_sequence_ = kMaxSequenceNumber;
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current_user_key_snapshot_ = 0;
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// apply the compaction filter to the first occurrence of the user key
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if (compaction_filter_ != nullptr && ikey_.type == kTypeValue &&
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(visible_at_tip_ || ikey_.sequence > latest_snapshot_ ||
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ignore_snapshots_)) {
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// If the user has specified a compaction filter and the sequence
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// number is greater than any external snapshot, then invoke the
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// filter. If the return value of the compaction filter is true,
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// replace the entry with a deletion marker.
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bool value_changed = false;
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bool to_delete = false;
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compaction_filter_value_.clear();
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{
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StopWatchNano timer(env_, true);
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to_delete = compaction_filter_->Filter(
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compaction_->level(), ikey_.user_key, value_,
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&compaction_filter_value_, &value_changed);
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iter_stats_.total_filter_time +=
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env_ != nullptr ? timer.ElapsedNanos() : 0;
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}
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if (to_delete) {
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// convert the current key to a delete
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ikey_.type = kTypeDeletion;
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current_key_.UpdateInternalKey(ikey_.sequence, kTypeDeletion);
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// no value associated with delete
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value_.clear();
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iter_stats_.num_record_drop_user++;
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} else if (value_changed) {
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value_ = compaction_filter_value_;
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}
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}
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} else {
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// Update the current key to reflect the new sequence number/type without
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// copying the user key.
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// TODO(rven): Compaction filter does not process keys in this path
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// Need to have the compaction filter process multiple versions
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// if we have versions on both sides of a snapshot
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current_key_.UpdateInternalKey(ikey_.sequence, ikey_.type);
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key_ = current_key_.GetKey();
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ikey_.user_key = current_key_.GetUserKey();
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}
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// If there are no snapshots, then this kv affect visibility at tip.
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// Otherwise, search though all existing snapshots to find the earliest
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// snapshot that is affected by this kv.
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SequenceNumber last_sequence __attribute__((__unused__)) =
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current_user_key_sequence_;
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current_user_key_sequence_ = ikey_.sequence;
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SequenceNumber last_snapshot = current_user_key_snapshot_;
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SequenceNumber prev_snapshot = 0; // 0 means no previous snapshot
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current_user_key_snapshot_ =
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visible_at_tip_
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? earliest_snapshot_
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: findEarliestVisibleSnapshot(ikey_.sequence, &prev_snapshot);
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if (clear_and_output_next_key_) {
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// In the previous iteration we encountered a single delete that we could
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// not compact out. We will keep this Put, but can drop it's data.
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// (See Optimization 3, below.)
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assert(ikey_.type == kTypeValue);
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assert(current_user_key_snapshot_ == last_snapshot);
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value_.clear();
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valid_ = true;
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clear_and_output_next_key_ = false;
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} else if (ikey_.type == kTypeSingleDeletion) {
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// We can compact out a SingleDelete if:
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// 1) We encounter the corresponding PUT -OR- we know that this key
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// doesn't appear past this output level
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// =AND=
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// 2) We've already returned a record in this snapshot -OR-
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// there are no earlier earliest_write_conflict_snapshot.
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//
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// Rule 1 is needed for SingleDelete correctness. Rule 2 is needed to
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// allow Transactions to do write-conflict checking (if we compacted away
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// all keys, then we wouldn't know that a write happened in this
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// snapshot). If there is no earlier snapshot, then we know that there
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// are no active transactions that need to know about any writes.
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//
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// Optimization 3:
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// If we encounter a SingleDelete followed by a PUT and Rule 2 is NOT
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// true, then we must output a SingleDelete. In this case, we will decide
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// to also output the PUT. While we are compacting less by outputting the
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// PUT now, hopefully this will lead to better compaction in the future
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// when Rule 2 is later true (Ie, We are hoping we can later compact out
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// both the SingleDelete and the Put, while we couldn't if we only
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// outputted the SingleDelete now).
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// In this case, we can save space by removing the PUT's value as it will
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// never be read.
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//
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// Deletes and Merges are not supported on the same key that has a
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// SingleDelete as it is not possible to correctly do any partial
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// compaction of such a combination of operations. The result of mixing
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// those operations for a given key is documented as being undefined. So
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// we can choose how to handle such a combinations of operations. We will
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// try to compact out as much as we can in these cases.
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// We will report counts on these anomalous cases.
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// The easiest way to process a SingleDelete during iteration is to peek
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// ahead at the next key.
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ParsedInternalKey next_ikey;
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input_->Next();
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// Check whether the next key exists, is not corrupt, and is the same key
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// as the single delete.
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if (input_->Valid() && ParseInternalKey(input_->key(), &next_ikey) &&
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cmp_->Equal(ikey_.user_key, next_ikey.user_key)) {
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// Check whether the next key belongs to the same snapshot as the
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// SingleDelete.
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if (prev_snapshot == 0 || next_ikey.sequence > prev_snapshot) {
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if (next_ikey.type == kTypeSingleDeletion) {
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// We encountered two SingleDeletes in a row. This could be due to
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// unexpected user input.
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// Skip the first SingleDelete and let the next iteration decide how
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// to handle the second SingleDelete
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// First SingleDelete has been skipped since we already called
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// input_->Next().
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++iter_stats_.num_record_drop_obsolete;
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++iter_stats_.num_single_del_mismatch;
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} else if ((ikey_.sequence <= earliest_write_conflict_snapshot_) ||
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has_outputted_key_) {
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// Found a matching value, we can drop the single delete and the
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// value. It is safe to drop both records since we've already
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// outputted a key in this snapshot, or there is no earlier
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// snapshot (Rule 2 above).
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// Note: it doesn't matter whether the second key is a Put or if it
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// is an unexpected Merge or Delete. We will compact it out
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// either way. We will maintain counts of how many mismatches
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// happened
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if (next_ikey.type != kTypeValue) {
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++iter_stats_.num_single_del_mismatch;
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}
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++iter_stats_.num_record_drop_hidden;
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++iter_stats_.num_record_drop_obsolete;
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// Already called input_->Next() once. Call it a second time to
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// skip past the second key.
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input_->Next();
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} else {
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// Found a matching value, but we cannot drop both keys since
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// there is an earlier snapshot and we need to leave behind a record
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// to know that a write happened in this snapshot (Rule 2 above).
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// Clear the value and output the SingleDelete. (The value will be
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// outputted on the next iteration.)
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// Setting valid_ to true will output the current SingleDelete
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valid_ = true;
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// Set up the Put to be outputted in the next iteration.
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// (Optimization 3).
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clear_and_output_next_key_ = true;
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}
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} else {
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// We hit the next snapshot without hitting a put, so the iterator
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// returns the single delete.
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valid_ = true;
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}
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} else {
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// We are at the end of the input, could not parse the next key, or hit
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// a different key. The iterator returns the single delete if the key
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// possibly exists beyond the current output level. We set
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// has_current_user_key to false so that if the iterator is at the next
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// key, we do not compare it again against the previous key at the next
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// iteration. If the next key is corrupt, we return before the
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// comparison, so the value of has_current_user_key does not matter.
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has_current_user_key_ = false;
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if (compaction_ != nullptr && ikey_.sequence <= earliest_snapshot_ &&
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compaction_->KeyNotExistsBeyondOutputLevel(ikey_.user_key,
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&level_ptrs_)) {
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// Key doesn't exist outside of this range.
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// Can compact out this SingleDelete.
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++iter_stats_.num_record_drop_obsolete;
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++iter_stats_.num_single_del_fallthru;
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} else {
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// Output SingleDelete
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valid_ = true;
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}
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}
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if (valid_) {
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at_next_ = true;
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}
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} else if (last_snapshot == current_user_key_snapshot_) {
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// If the earliest snapshot is which this key is visible in
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// is the same as the visibility of a previous instance of the
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// same key, then this kv is not visible in any snapshot.
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// Hidden by an newer entry for same user key
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// TODO: why not > ?
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//
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// Note: Dropping this key will not affect TransactionDB write-conflict
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// checking since there has already been a record returned for this key
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// in this snapshot.
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assert(last_sequence >= current_user_key_sequence_);
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++iter_stats_.num_record_drop_hidden; // (A)
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input_->Next();
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} else if (compaction_ != nullptr && ikey_.type == kTypeDeletion &&
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ikey_.sequence <= earliest_snapshot_ &&
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compaction_->KeyNotExistsBeyondOutputLevel(ikey_.user_key,
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&level_ptrs_)) {
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// TODO(noetzli): This is the only place where we use compaction_
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// (besides the constructor). We should probably get rid of this
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// dependency and find a way to do similar filtering during flushes.
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//
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// For this user key:
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// (1) there is no data in higher levels
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// (2) data in lower levels will have larger sequence numbers
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// (3) data in layers that are being compacted here and have
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// smaller sequence numbers will be dropped in the next
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// few iterations of this loop (by rule (A) above).
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// Therefore this deletion marker is obsolete and can be dropped.
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//
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// Note: Dropping this Delete will not affect TransactionDB
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// write-conflict checking since it is earlier than any snapshot.
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++iter_stats_.num_record_drop_obsolete;
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input_->Next();
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} else if (ikey_.type == kTypeMerge) {
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if (!merge_helper_->HasOperator()) {
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LogToBuffer(log_buffer_, "Options::merge_operator is null.");
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status_ = Status::InvalidArgument(
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"merge_operator is not properly initialized.");
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return;
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}
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pinned_iters_mgr_.StartPinning();
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// We know the merge type entry is not hidden, otherwise we would
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// have hit (A)
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// We encapsulate the merge related state machine in a different
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// object to minimize change to the existing flow.
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merge_helper_->MergeUntil(input_, range_del_agg_, prev_snapshot,
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bottommost_level_);
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merge_out_iter_.SeekToFirst();
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if (merge_out_iter_.Valid()) {
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// NOTE: key, value, and ikey_ refer to old entries.
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// These will be correctly set below.
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key_ = merge_out_iter_.key();
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value_ = merge_out_iter_.value();
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bool valid_key __attribute__((__unused__)) =
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ParseInternalKey(key_, &ikey_);
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// MergeUntil stops when it encounters a corrupt key and does not
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// include them in the result, so we expect the keys here to valid.
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assert(valid_key);
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// Keep current_key_ in sync.
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current_key_.UpdateInternalKey(ikey_.sequence, ikey_.type);
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key_ = current_key_.GetKey();
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ikey_.user_key = current_key_.GetUserKey();
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valid_ = true;
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} else {
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// all merge operands were filtered out. reset the user key, since the
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// batch consumed by the merge operator should not shadow any keys
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// coming after the merges
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has_current_user_key_ = false;
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pinned_iters_mgr_.ReleasePinnedData();
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}
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} else {
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// 1. new user key -OR-
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// 2. different snapshot stripe
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bool should_delete = range_del_agg_->ShouldDelete(key_);
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if (should_delete) {
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++iter_stats_.num_record_drop_hidden;
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++iter_stats_.num_record_drop_range_del;
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input_->Next();
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} else {
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valid_ = true;
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}
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}
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}
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}
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void CompactionIterator::PrepareOutput() {
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// Zeroing out the sequence number leads to better compression.
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// If this is the bottommost level (no files in lower levels)
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// and the earliest snapshot is larger than this seqno
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// and the userkey differs from the last userkey in compaction
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// then we can squash the seqno to zero.
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// This is safe for TransactionDB write-conflict checking since transactions
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// only care about sequence number larger than any active snapshots.
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if (bottommost_level_ && valid_ && ikey_.sequence < earliest_snapshot_ &&
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ikey_.type != kTypeMerge &&
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!cmp_->Equal(compaction_->GetLargestUserKey(), ikey_.user_key)) {
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assert(ikey_.type != kTypeDeletion && ikey_.type != kTypeSingleDeletion);
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ikey_.sequence = 0;
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current_key_.UpdateInternalKey(0, ikey_.type);
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}
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}
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inline SequenceNumber CompactionIterator::findEarliestVisibleSnapshot(
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SequenceNumber in, SequenceNumber* prev_snapshot) {
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assert(snapshots_->size());
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|
SequenceNumber prev __attribute__((__unused__)) = kMaxSequenceNumber;
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for (const auto cur : *snapshots_) {
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|
assert(prev == kMaxSequenceNumber || prev <= cur);
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|
if (cur >= in) {
|
|
*prev_snapshot = prev == kMaxSequenceNumber ? 0 : prev;
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|
return cur;
|
|
}
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|
prev = cur;
|
|
assert(prev < kMaxSequenceNumber);
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|
}
|
|
*prev_snapshot = prev;
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return kMaxSequenceNumber;
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}
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} // namespace rocksdb
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