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b7fbcefda8
Summary: Prior to this PR, `FullMergeV2()` can only return `false` to indicate failure, which causes any operation invoking it to fail. During a compaction, such a failure causes the compaction to fail and causes the DB to irreversibly enter read-only mode. Some users asked for a way to allow the merge operator to fail without such widespread damage. To limit the blast radius of merge operator failures, this PR introduces the `MergeOperationOutput::op_failure_scope` API. When unpopulated (`kDefault`) or set to `kTryMerge`, the merge operator failure handling is the same as before. When set to `kMustMerge`, merge operator failure still causes failure to operations that must merge (`Get()`, iterator, `MultiGet()`, etc.). However, under `kMustMerge`, flushes/compactions can survive merge operator failures by outputting the unmerged input operands. Pull Request resolved: https://github.com/facebook/rocksdb/pull/11092 Reviewed By: siying Differential Revision: D42525673 Pulled By: ajkr fbshipit-source-id: 951dc3bf190f86347dccf3381be967565cda52ee
602 lines
23 KiB
C++
602 lines
23 KiB
C++
// Copyright (c) 2011-present, Facebook, Inc. All rights reserved.
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// This source code is licensed under both the GPLv2 (found in the
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// COPYING file in the root directory) and Apache 2.0 License
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// (found in the LICENSE.Apache file in the root directory).
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#include "db/merge_helper.h"
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#include <string>
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#include "db/blob/blob_fetcher.h"
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#include "db/blob/blob_index.h"
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#include "db/blob/prefetch_buffer_collection.h"
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#include "db/compaction/compaction_iteration_stats.h"
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#include "db/dbformat.h"
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#include "db/wide/wide_column_serialization.h"
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#include "logging/logging.h"
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#include "monitoring/perf_context_imp.h"
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#include "monitoring/statistics.h"
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#include "port/likely.h"
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#include "rocksdb/comparator.h"
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#include "rocksdb/db.h"
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#include "rocksdb/merge_operator.h"
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#include "rocksdb/system_clock.h"
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#include "table/format.h"
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#include "table/internal_iterator.h"
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namespace ROCKSDB_NAMESPACE {
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MergeHelper::MergeHelper(Env* env, const Comparator* user_comparator,
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const MergeOperator* user_merge_operator,
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const CompactionFilter* compaction_filter,
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Logger* logger, bool assert_valid_internal_key,
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SequenceNumber latest_snapshot,
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const SnapshotChecker* snapshot_checker, int level,
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Statistics* stats,
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const std::atomic<bool>* shutting_down)
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: env_(env),
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clock_(env->GetSystemClock().get()),
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user_comparator_(user_comparator),
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user_merge_operator_(user_merge_operator),
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compaction_filter_(compaction_filter),
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shutting_down_(shutting_down),
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logger_(logger),
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assert_valid_internal_key_(assert_valid_internal_key),
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allow_single_operand_(false),
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latest_snapshot_(latest_snapshot),
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snapshot_checker_(snapshot_checker),
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level_(level),
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keys_(),
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filter_timer_(clock_),
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total_filter_time_(0U),
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stats_(stats) {
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assert(user_comparator_ != nullptr);
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if (user_merge_operator_) {
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allow_single_operand_ = user_merge_operator_->AllowSingleOperand();
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}
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}
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Status MergeHelper::TimedFullMerge(
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const MergeOperator* merge_operator, const Slice& key, const Slice* value,
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const std::vector<Slice>& operands, std::string* result, Logger* logger,
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Statistics* statistics, SystemClock* clock, Slice* result_operand,
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bool update_num_ops_stats,
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MergeOperator::OpFailureScope* op_failure_scope) {
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assert(merge_operator != nullptr);
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if (operands.empty()) {
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assert(value != nullptr && result != nullptr);
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result->assign(value->data(), value->size());
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return Status::OK();
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}
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if (update_num_ops_stats) {
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RecordInHistogram(statistics, READ_NUM_MERGE_OPERANDS,
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static_cast<uint64_t>(operands.size()));
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}
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bool success = false;
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Slice tmp_result_operand(nullptr, 0);
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const MergeOperator::MergeOperationInput merge_in(key, value, operands,
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logger);
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MergeOperator::MergeOperationOutput merge_out(*result, tmp_result_operand);
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{
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// Setup to time the merge
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StopWatchNano timer(clock, statistics != nullptr);
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PERF_TIMER_GUARD(merge_operator_time_nanos);
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// Do the merge
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success = merge_operator->FullMergeV2(merge_in, &merge_out);
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if (tmp_result_operand.data()) {
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// FullMergeV2 result is an existing operand
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if (result_operand != nullptr) {
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*result_operand = tmp_result_operand;
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} else {
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result->assign(tmp_result_operand.data(), tmp_result_operand.size());
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}
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} else if (result_operand) {
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*result_operand = Slice(nullptr, 0);
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}
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RecordTick(statistics, MERGE_OPERATION_TOTAL_TIME,
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statistics ? timer.ElapsedNanos() : 0);
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}
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if (op_failure_scope != nullptr) {
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*op_failure_scope = merge_out.op_failure_scope;
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// Apply default per merge_operator.h
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if (*op_failure_scope == MergeOperator::OpFailureScope::kDefault) {
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*op_failure_scope = MergeOperator::OpFailureScope::kTryMerge;
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}
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}
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if (!success) {
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RecordTick(statistics, NUMBER_MERGE_FAILURES);
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return Status::Corruption("Error: Could not perform merge.");
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}
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return Status::OK();
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}
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Status MergeHelper::TimedFullMergeWithEntity(
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const MergeOperator* merge_operator, const Slice& key, Slice base_entity,
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const std::vector<Slice>& operands, std::string* result, Logger* logger,
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Statistics* statistics, SystemClock* clock, bool update_num_ops_stats,
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MergeOperator::OpFailureScope* op_failure_scope) {
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WideColumns base_columns;
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{
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const Status s =
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WideColumnSerialization::Deserialize(base_entity, base_columns);
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if (!s.ok()) {
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return s;
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}
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}
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const bool has_default_column =
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!base_columns.empty() && base_columns[0].name() == kDefaultWideColumnName;
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Slice value_of_default;
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if (has_default_column) {
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value_of_default = base_columns[0].value();
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}
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std::string merge_result;
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{
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const Status s = TimedFullMerge(merge_operator, key, &value_of_default,
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operands, &merge_result, logger, statistics,
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clock, nullptr /* result_operand */,
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update_num_ops_stats, op_failure_scope);
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if (!s.ok()) {
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return s;
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}
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}
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if (has_default_column) {
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base_columns[0].value() = merge_result;
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const Status s = WideColumnSerialization::Serialize(base_columns, *result);
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if (!s.ok()) {
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return s;
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}
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} else {
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const Status s =
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WideColumnSerialization::Serialize(merge_result, base_columns, *result);
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if (!s.ok()) {
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return s;
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}
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}
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return Status::OK();
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}
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// PRE: iter points to the first merge type entry
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// POST: iter points to the first entry beyond the merge process (or the end)
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// keys_, operands_ are updated to reflect the merge result.
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// keys_ stores the list of keys encountered while merging.
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// operands_ stores the list of merge operands encountered while merging.
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// keys_[i] corresponds to operands_[i] for each i.
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//
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// TODO: Avoid the snapshot stripe map lookup in CompactionRangeDelAggregator
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// and just pass the StripeRep corresponding to the stripe being merged.
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Status MergeHelper::MergeUntil(InternalIterator* iter,
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CompactionRangeDelAggregator* range_del_agg,
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const SequenceNumber stop_before,
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const bool at_bottom,
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const bool allow_data_in_errors,
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const BlobFetcher* blob_fetcher,
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const std::string* const full_history_ts_low,
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PrefetchBufferCollection* prefetch_buffers,
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CompactionIterationStats* c_iter_stats) {
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// Get a copy of the internal key, before it's invalidated by iter->Next()
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// Also maintain the list of merge operands seen.
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assert(HasOperator());
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keys_.clear();
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merge_context_.Clear();
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has_compaction_filter_skip_until_ = false;
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assert(user_merge_operator_);
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assert(user_comparator_);
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const size_t ts_sz = user_comparator_->timestamp_size();
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if (full_history_ts_low) {
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assert(ts_sz > 0);
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assert(ts_sz == full_history_ts_low->size());
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}
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bool first_key = true;
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// We need to parse the internal key again as the parsed key is
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// backed by the internal key!
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// Assume no internal key corruption as it has been successfully parsed
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// by the caller.
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// original_key_is_iter variable is just caching the information:
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// original_key_is_iter == (iter->key().ToString() == original_key)
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bool original_key_is_iter = true;
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std::string original_key = iter->key().ToString();
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// Important:
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// orig_ikey is backed by original_key if keys_.empty()
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// orig_ikey is backed by keys_.back() if !keys_.empty()
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ParsedInternalKey orig_ikey;
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Status s = ParseInternalKey(original_key, &orig_ikey, allow_data_in_errors);
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assert(s.ok());
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if (!s.ok()) return s;
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assert(kTypeMerge == orig_ikey.type);
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bool hit_the_next_user_key = false;
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int cmp_with_full_history_ts_low = 0;
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for (; iter->Valid(); iter->Next(), original_key_is_iter = false) {
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if (IsShuttingDown()) {
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s = Status::ShutdownInProgress();
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return s;
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}
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ParsedInternalKey ikey;
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assert(keys_.size() == merge_context_.GetNumOperands());
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Status pik_status =
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ParseInternalKey(iter->key(), &ikey, allow_data_in_errors);
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Slice ts;
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if (pik_status.ok()) {
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ts = ExtractTimestampFromUserKey(ikey.user_key, ts_sz);
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if (full_history_ts_low) {
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cmp_with_full_history_ts_low =
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user_comparator_->CompareTimestamp(ts, *full_history_ts_low);
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}
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}
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if (!pik_status.ok()) {
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// stop at corrupted key
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if (assert_valid_internal_key_) {
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return pik_status;
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}
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break;
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} else if (first_key) {
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// If user-defined timestamp is enabled, we expect both user key and
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// timestamps are equal, as a sanity check.
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assert(user_comparator_->Equal(ikey.user_key, orig_ikey.user_key));
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first_key = false;
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} else if (!user_comparator_->EqualWithoutTimestamp(ikey.user_key,
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orig_ikey.user_key) ||
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(ts_sz > 0 &&
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!user_comparator_->Equal(ikey.user_key, orig_ikey.user_key) &&
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cmp_with_full_history_ts_low >= 0)) {
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// 1) hit a different user key, or
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// 2) user-defined timestamp is enabled, and hit a version of user key NOT
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// eligible for GC, then stop right here.
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hit_the_next_user_key = true;
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break;
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} else if (stop_before > 0 && ikey.sequence <= stop_before &&
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LIKELY(snapshot_checker_ == nullptr ||
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snapshot_checker_->CheckInSnapshot(ikey.sequence,
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stop_before) !=
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SnapshotCheckerResult::kNotInSnapshot)) {
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// hit an entry that's possibly visible by the previous snapshot, can't
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// touch that
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break;
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}
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// At this point we are guaranteed that we need to process this key.
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assert(IsValueType(ikey.type));
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if (ikey.type != kTypeMerge) {
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// hit a put/delete/single delete
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// => merge the put value or a nullptr with operands_
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// => store result in operands_.back() (and update keys_.back())
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// => change the entry type to kTypeValue for keys_.back()
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// We are done! Success!
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// If there are no operands, just return the Status::OK(). That will cause
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// the compaction iterator to write out the key we're currently at, which
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// is the put/delete we just encountered.
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if (keys_.empty()) {
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return s;
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}
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// TODO: if we're in compaction and it's a put, it would be nice to run
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// compaction filter on it.
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std::string merge_result;
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MergeOperator::OpFailureScope op_failure_scope;
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if (range_del_agg &&
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range_del_agg->ShouldDelete(
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ikey, RangeDelPositioningMode::kForwardTraversal)) {
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s = TimedFullMerge(user_merge_operator_, ikey.user_key, nullptr,
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merge_context_.GetOperands(), &merge_result, logger_,
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stats_, clock_,
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/* result_operand */ nullptr,
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/* update_num_ops_stats */ false, &op_failure_scope);
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} else if (ikey.type == kTypeValue) {
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const Slice val = iter->value();
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s = TimedFullMerge(user_merge_operator_, ikey.user_key, &val,
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merge_context_.GetOperands(), &merge_result, logger_,
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stats_, clock_,
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/* result_operand */ nullptr,
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/* update_num_ops_stats */ false, &op_failure_scope);
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} else if (ikey.type == kTypeBlobIndex) {
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BlobIndex blob_index;
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s = blob_index.DecodeFrom(iter->value());
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if (!s.ok()) {
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return s;
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}
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FilePrefetchBuffer* prefetch_buffer =
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prefetch_buffers ? prefetch_buffers->GetOrCreatePrefetchBuffer(
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blob_index.file_number())
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: nullptr;
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uint64_t bytes_read = 0;
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assert(blob_fetcher);
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PinnableSlice blob_value;
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s = blob_fetcher->FetchBlob(ikey.user_key, blob_index, prefetch_buffer,
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&blob_value, &bytes_read);
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if (!s.ok()) {
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return s;
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}
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if (c_iter_stats) {
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++c_iter_stats->num_blobs_read;
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c_iter_stats->total_blob_bytes_read += bytes_read;
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}
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s = TimedFullMerge(user_merge_operator_, ikey.user_key, &blob_value,
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merge_context_.GetOperands(), &merge_result, logger_,
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stats_, clock_,
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/* result_operand */ nullptr,
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/* update_num_ops_stats */ false, &op_failure_scope);
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} else if (ikey.type == kTypeWideColumnEntity) {
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s = TimedFullMergeWithEntity(
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user_merge_operator_, ikey.user_key, iter->value(),
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merge_context_.GetOperands(), &merge_result, logger_, stats_,
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clock_, /* update_num_ops_stats */ false, &op_failure_scope);
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} else {
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s = TimedFullMerge(user_merge_operator_, ikey.user_key, nullptr,
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merge_context_.GetOperands(), &merge_result, logger_,
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stats_, clock_,
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/* result_operand */ nullptr,
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/* update_num_ops_stats */ false, &op_failure_scope);
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}
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// We store the result in keys_.back() and operands_.back()
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// if nothing went wrong (i.e.: no operand corruption on disk)
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if (s.ok()) {
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// The original key encountered
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original_key = std::move(keys_.back());
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orig_ikey.type = ikey.type == kTypeWideColumnEntity
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? kTypeWideColumnEntity
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: kTypeValue;
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UpdateInternalKey(&original_key, orig_ikey.sequence, orig_ikey.type);
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keys_.clear();
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merge_context_.Clear();
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keys_.emplace_front(std::move(original_key));
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merge_context_.PushOperand(merge_result);
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// move iter to the next entry
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iter->Next();
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} else if (op_failure_scope ==
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MergeOperator::OpFailureScope::kMustMerge) {
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// Change to `Status::MergeInProgress()` to denote output consists of
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// merge operands only. Leave `iter` at the non-merge entry so it will
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// be output after.
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s = Status::MergeInProgress();
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}
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return s;
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} else {
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// hit a merge
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// => if there is a compaction filter, apply it.
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// => check for range tombstones covering the operand
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// => merge the operand into the front of the operands_ list
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// if not filtered
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// => then continue because we haven't yet seen a Put/Delete.
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//
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// Keep queuing keys and operands until we either meet a put / delete
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// request or later did a partial merge.
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Slice value_slice = iter->value();
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// add an operand to the list if:
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// 1) it's included in one of the snapshots. in that case we *must* write
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// it out, no matter what compaction filter says
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// 2) it's not filtered by a compaction filter
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CompactionFilter::Decision filter =
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ikey.sequence <= latest_snapshot_
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? CompactionFilter::Decision::kKeep
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: FilterMerge(orig_ikey.user_key, value_slice);
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if (filter != CompactionFilter::Decision::kRemoveAndSkipUntil &&
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range_del_agg != nullptr &&
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range_del_agg->ShouldDelete(
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iter->key(), RangeDelPositioningMode::kForwardTraversal)) {
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filter = CompactionFilter::Decision::kRemove;
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}
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if (filter == CompactionFilter::Decision::kKeep ||
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filter == CompactionFilter::Decision::kChangeValue) {
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if (original_key_is_iter) {
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// this is just an optimization that saves us one memcpy
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keys_.emplace_front(original_key);
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} else {
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keys_.emplace_front(iter->key().ToString());
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}
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if (keys_.size() == 1) {
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// we need to re-anchor the orig_ikey because it was anchored by
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// original_key before
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pik_status =
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ParseInternalKey(keys_.back(), &orig_ikey, allow_data_in_errors);
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pik_status.PermitUncheckedError();
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assert(pik_status.ok());
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}
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if (filter == CompactionFilter::Decision::kKeep) {
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merge_context_.PushOperand(
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value_slice, iter->IsValuePinned() /* operand_pinned */);
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} else {
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assert(filter == CompactionFilter::Decision::kChangeValue);
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// Compaction filter asked us to change the operand from value_slice
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// to compaction_filter_value_.
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merge_context_.PushOperand(compaction_filter_value_, false);
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}
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} else if (filter == CompactionFilter::Decision::kRemoveAndSkipUntil) {
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// Compaction filter asked us to remove this key altogether
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// (not just this operand), along with some keys following it.
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keys_.clear();
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merge_context_.Clear();
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has_compaction_filter_skip_until_ = true;
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return s;
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}
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}
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}
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if (cmp_with_full_history_ts_low >= 0) {
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size_t num_merge_operands = merge_context_.GetNumOperands();
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if (ts_sz && num_merge_operands > 1) {
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// We do not merge merge operands with different timestamps if they are
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// not eligible for GC.
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ROCKS_LOG_ERROR(logger_, "ts_sz=%d, %d merge oprands",
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static_cast<int>(ts_sz),
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static_cast<int>(num_merge_operands));
|
|
assert(false);
|
|
}
|
|
}
|
|
|
|
if (merge_context_.GetNumOperands() == 0) {
|
|
// we filtered out all the merge operands
|
|
return s;
|
|
}
|
|
|
|
// We are sure we have seen this key's entire history if:
|
|
// at_bottom == true (this does not necessarily mean it is the bottommost
|
|
// layer, but rather that we are confident the key does not appear on any of
|
|
// the lower layers, at_bottom == false doesn't mean it does appear, just
|
|
// that we can't be sure, see Compaction::IsBottommostLevel for details)
|
|
// AND
|
|
// we have either encountered another key or end of key history on this
|
|
// layer.
|
|
// Note that if user-defined timestamp is enabled, we need some extra caution
|
|
// here: if full_history_ts_low is nullptr, or it's not null but the key's
|
|
// timestamp is greater than or equal to full_history_ts_low, it means this
|
|
// key cannot be dropped. We may not have seen the beginning of the key.
|
|
//
|
|
// When these conditions are true we are able to merge all the keys
|
|
// using full merge.
|
|
//
|
|
// For these cases we are not sure about, 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.
|
|
bool surely_seen_the_beginning =
|
|
(hit_the_next_user_key || !iter->Valid()) && at_bottom &&
|
|
(ts_sz == 0 || cmp_with_full_history_ts_low < 0);
|
|
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;
|
|
MergeOperator::OpFailureScope op_failure_scope;
|
|
s = TimedFullMerge(user_merge_operator_, orig_ikey.user_key, nullptr,
|
|
merge_context_.GetOperands(), &merge_result, logger_,
|
|
stats_, clock_,
|
|
/* result_operand */ nullptr,
|
|
/* update_num_ops_stats */ false, &op_failure_scope);
|
|
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 if (op_failure_scope == MergeOperator::OpFailureScope::kMustMerge) {
|
|
// Change to `Status::MergeInProgress()` to denote output consists of
|
|
// merge operands only.
|
|
s = Status::MergeInProgress();
|
|
}
|
|
} 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.
|
|
s = Status::MergeInProgress();
|
|
if (merge_context_.GetNumOperands() >= 2 ||
|
|
(allow_single_operand_ && merge_context_.GetNumOperands() == 1)) {
|
|
bool merge_success = false;
|
|
std::string merge_result;
|
|
{
|
|
StopWatchNano timer(clock_, 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 && ShouldReportDetailedTime(env_, stats_)) {
|
|
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);
|
|
}
|
|
}
|
|
if (stats_ != nullptr && ShouldReportDetailedTime(env_, stats_)) {
|
|
total_filter_time_ += filter_timer_.ElapsedNanosSafe();
|
|
}
|
|
return ret;
|
|
}
|
|
|
|
} // namespace ROCKSDB_NAMESPACE
|