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rocksdb/db/compaction/compaction_iterator.cc

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// Copyright (c) 2011-present, Facebook, Inc. All rights reserved.
// This source code is licensed under both the GPLv2 (found in the
// COPYING file in the root directory) and Apache 2.0 License
// (found in the LICENSE.Apache file in the root directory).
#include "db/compaction/compaction_iterator.h"
#include <iterator>
#include <limits>
#include "db/blob/blob_fetcher.h"
#include "db/blob/blob_file_builder.h"
#include "db/blob/blob_index.h"
#include "db/blob/prefetch_buffer_collection.h"
#include "db/snapshot_checker.h"
#include "logging/logging.h"
#include "port/likely.h"
#include "rocksdb/listener.h"
#include "table/internal_iterator.h"
#include "test_util/sync_point.h"
namespace ROCKSDB_NAMESPACE {
CompactionIterator::CompactionIterator(
InternalIterator* input, const Comparator* cmp, MergeHelper* merge_helper,
SequenceNumber last_sequence, std::vector<SequenceNumber>* snapshots,
SequenceNumber earliest_write_conflict_snapshot,
SequenceNumber job_snapshot, const SnapshotChecker* snapshot_checker,
Env* env, bool report_detailed_time, bool expect_valid_internal_key,
CompactionRangeDelAggregator* range_del_agg,
BlobFileBuilder* blob_file_builder, bool allow_data_in_errors,
bool enforce_single_del_contracts,
const std::atomic<bool>& manual_compaction_canceled,
const Compaction* compaction, const CompactionFilter* compaction_filter,
const std::atomic<bool>* shutting_down,
const std::shared_ptr<Logger> info_log,
const std::string* full_history_ts_low,
const SequenceNumber preserve_time_min_seqno,
const SequenceNumber preclude_last_level_min_seqno)
: CompactionIterator(
input, cmp, merge_helper, last_sequence, snapshots,
earliest_write_conflict_snapshot, job_snapshot, snapshot_checker, env,
report_detailed_time, expect_valid_internal_key, range_del_agg,
blob_file_builder, allow_data_in_errors, enforce_single_del_contracts,
manual_compaction_canceled,
std::unique_ptr<CompactionProxy>(
compaction ? new RealCompaction(compaction) : nullptr),
compaction_filter, shutting_down, info_log, full_history_ts_low,
preserve_time_min_seqno, preclude_last_level_min_seqno) {}
CompactionIterator::CompactionIterator(
InternalIterator* input, const Comparator* cmp, MergeHelper* merge_helper,
SequenceNumber /*last_sequence*/, std::vector<SequenceNumber>* snapshots,
SequenceNumber earliest_write_conflict_snapshot,
SequenceNumber job_snapshot, const SnapshotChecker* snapshot_checker,
Env* env, bool report_detailed_time, bool expect_valid_internal_key,
CompactionRangeDelAggregator* range_del_agg,
BlobFileBuilder* blob_file_builder, bool allow_data_in_errors,
bool enforce_single_del_contracts,
const std::atomic<bool>& manual_compaction_canceled,
std::unique_ptr<CompactionProxy> compaction,
const CompactionFilter* compaction_filter,
const std::atomic<bool>* shutting_down,
const std::shared_ptr<Logger> info_log,
const std::string* full_history_ts_low,
const SequenceNumber preserve_time_min_seqno,
const SequenceNumber preclude_last_level_min_seqno)
: input_(input, cmp,
!compaction || compaction->DoesInputReferenceBlobFiles()),
cmp_(cmp),
merge_helper_(merge_helper),
snapshots_(snapshots),
earliest_write_conflict_snapshot_(earliest_write_conflict_snapshot),
job_snapshot_(job_snapshot),
snapshot_checker_(snapshot_checker),
env_(env),
clock_(env_->GetSystemClock().get()),
report_detailed_time_(report_detailed_time),
expect_valid_internal_key_(expect_valid_internal_key),
range_del_agg_(range_del_agg),
blob_file_builder_(blob_file_builder),
compaction_(std::move(compaction)),
compaction_filter_(compaction_filter),
shutting_down_(shutting_down),
manual_compaction_canceled_(manual_compaction_canceled),
bottommost_level_(!compaction_ ? false
: compaction_->bottommost_level() &&
!compaction_->allow_ingest_behind()),
// snapshots_ cannot be nullptr, but we will assert later in the body of
// the constructor.
visible_at_tip_(snapshots_ ? snapshots_->empty() : false),
earliest_snapshot_(!snapshots_ || snapshots_->empty()
? kMaxSequenceNumber
: snapshots_->at(0)),
info_log_(info_log),
allow_data_in_errors_(allow_data_in_errors),
enforce_single_del_contracts_(enforce_single_del_contracts),
timestamp_size_(cmp_ ? cmp_->timestamp_size() : 0),
full_history_ts_low_(full_history_ts_low),
current_user_key_sequence_(0),
current_user_key_snapshot_(0),
merge_out_iter_(merge_helper_),
blob_garbage_collection_cutoff_file_number_(
ComputeBlobGarbageCollectionCutoffFileNumber(compaction_.get())),
blob_fetcher_(CreateBlobFetcherIfNeeded(compaction_.get())),
prefetch_buffers_(
CreatePrefetchBufferCollectionIfNeeded(compaction_.get())),
current_key_committed_(false),
cmp_with_history_ts_low_(0),
level_(compaction_ == nullptr ? 0 : compaction_->level()),
preserve_time_min_seqno_(preserve_time_min_seqno),
preclude_last_level_min_seqno_(preclude_last_level_min_seqno) {
assert(snapshots_ != nullptr);
assert(preserve_time_min_seqno_ <= preclude_last_level_min_seqno_);
if (compaction_ != nullptr) {
level_ptrs_ = std::vector<size_t>(compaction_->number_levels(), 0);
}
#ifndef NDEBUG
// findEarliestVisibleSnapshot assumes this ordering.
for (size_t i = 1; i < snapshots_->size(); ++i) {
assert(snapshots_->at(i - 1) < snapshots_->at(i));
}
assert(timestamp_size_ == 0 || !full_history_ts_low_ ||
timestamp_size_ == full_history_ts_low_->size());
#endif
input_.SetPinnedItersMgr(&pinned_iters_mgr_);
TEST_SYNC_POINT_CALLBACK("CompactionIterator:AfterInit", compaction_.get());
}
CompactionIterator::~CompactionIterator() {
// input_ Iterator lifetime is longer than pinned_iters_mgr_ lifetime
input_.SetPinnedItersMgr(nullptr);
}
void CompactionIterator::ResetRecordCounts() {
iter_stats_.num_record_drop_user = 0;
iter_stats_.num_record_drop_hidden = 0;
iter_stats_.num_record_drop_obsolete = 0;
iter_stats_.num_record_drop_range_del = 0;
iter_stats_.num_range_del_drop_obsolete = 0;
iter_stats_.num_optimized_del_drop_obsolete = 0;
}
void CompactionIterator::SeekToFirst() {
NextFromInput();
PrepareOutput();
}
void CompactionIterator::Next() {
// If there is a merge output, return it before continuing to process the
// input.
if (merge_out_iter_.Valid()) {
merge_out_iter_.Next();
// Check if we returned all records of the merge output.
if (merge_out_iter_.Valid()) {
key_ = merge_out_iter_.key();
value_ = merge_out_iter_.value();
Status s = ParseInternalKey(key_, &ikey_, allow_data_in_errors_);
// MergeUntil stops when it encounters a corrupt key and does not
// include them in the result, so we expect the keys here to be valid.
if (!s.ok()) {
ROCKS_LOG_FATAL(
info_log_, "Invalid ikey %s in compaction. %s",
allow_data_in_errors_ ? key_.ToString(true).c_str() : "hidden",
s.getState());
assert(false);
}
// Keep current_key_ in sync.
current_key_.UpdateInternalKey(ikey_.sequence, ikey_.type);
key_ = current_key_.GetInternalKey();
ikey_.user_key = current_key_.GetUserKey();
validity_info_.SetValid(ValidContext::kMerge1);
} else {
// We consumed all pinned merge operands, release pinned iterators
pinned_iters_mgr_.ReleasePinnedData();
// MergeHelper moves the iterator to the first record after the merged
// records, so even though we reached the end of the merge output, we do
// not want to advance the iterator.
NextFromInput();
}
} else {
// Only advance the input iterator if there is no merge output and the
// iterator is not already at the next record.
if (!at_next_) {
AdvanceInputIter();
}
NextFromInput();
}
if (Valid()) {
// Record that we've outputted a record for the current key.
has_outputted_key_ = true;
}
PrepareOutput();
}
bool CompactionIterator::InvokeFilterIfNeeded(bool* need_skip,
Slice* skip_until) {
// TODO: support compaction filter for wide-column entities
if (!compaction_filter_ ||
(ikey_.type != kTypeValue && ikey_.type != kTypeBlobIndex)) {
return true;
}
bool error = false;
// If the user has specified a compaction filter and the sequence
// number is greater than any external snapshot, then invoke the
// filter. If the return value of the compaction filter is true,
// replace the entry with a deletion marker.
CompactionFilter::Decision filter = CompactionFilter::Decision::kUndetermined;
compaction_filter_value_.clear();
compaction_filter_skip_until_.Clear();
CompactionFilter::ValueType value_type =
ikey_.type == kTypeValue ? CompactionFilter::ValueType::kValue
: CompactionFilter::ValueType::kBlobIndex;
// Hack: pass internal key to BlobIndexCompactionFilter since it needs
// to get sequence number.
assert(compaction_filter_);
Slice& filter_key =
(ikey_.type == kTypeValue ||
!compaction_filter_->IsStackedBlobDbInternalCompactionFilter())
? ikey_.user_key
: key_;
{
StopWatchNano timer(clock_, report_detailed_time_);
if (kTypeBlobIndex == ikey_.type) {
filter = compaction_filter_->FilterBlobByKey(
level_, filter_key, &compaction_filter_value_,
compaction_filter_skip_until_.rep());
if (CompactionFilter::Decision::kUndetermined == filter &&
!compaction_filter_->IsStackedBlobDbInternalCompactionFilter()) {
if (compaction_ == nullptr) {
status_ =
Status::Corruption("Unexpected blob index outside of compaction");
validity_info_.Invalidate();
return false;
}
TEST_SYNC_POINT_CALLBACK(
"CompactionIterator::InvokeFilterIfNeeded::TamperWithBlobIndex",
&value_);
// For integrated BlobDB impl, CompactionIterator reads blob value.
// For Stacked BlobDB impl, the corresponding CompactionFilter's
// FilterV2 method should read the blob value.
BlobIndex blob_index;
Status s = blob_index.DecodeFrom(value_);
if (!s.ok()) {
status_ = s;
validity_info_.Invalidate();
return false;
}
FilePrefetchBuffer* prefetch_buffer =
prefetch_buffers_ ? prefetch_buffers_->GetOrCreatePrefetchBuffer(
blob_index.file_number())
: nullptr;
uint64_t bytes_read = 0;
assert(blob_fetcher_);
s = blob_fetcher_->FetchBlob(ikey_.user_key, blob_index,
prefetch_buffer, &blob_value_,
&bytes_read);
if (!s.ok()) {
status_ = s;
validity_info_.Invalidate();
return false;
}
++iter_stats_.num_blobs_read;
iter_stats_.total_blob_bytes_read += bytes_read;
value_type = CompactionFilter::ValueType::kValue;
}
}
if (CompactionFilter::Decision::kUndetermined == filter) {
filter = compaction_filter_->FilterV2(
level_, filter_key, value_type,
blob_value_.empty() ? value_ : blob_value_, &compaction_filter_value_,
compaction_filter_skip_until_.rep());
}
iter_stats_.total_filter_time +=
env_ != nullptr && report_detailed_time_ ? timer.ElapsedNanos() : 0;
}
if (CompactionFilter::Decision::kUndetermined == filter) {
// Should not reach here, since FilterV2 should never return kUndetermined.
status_ =
Status::NotSupported("FilterV2() should never return kUndetermined");
validity_info_.Invalidate();
return false;
}
if (filter == CompactionFilter::Decision::kRemoveAndSkipUntil &&
cmp_->Compare(*compaction_filter_skip_until_.rep(), ikey_.user_key) <=
0) {
// Can't skip to a key smaller than the current one.
// Keep the key as per FilterV2 documentation.
filter = CompactionFilter::Decision::kKeep;
}
if (filter == CompactionFilter::Decision::kRemove) {
// convert the current key to a delete; key_ is pointing into
// current_key_ at this point, so updating current_key_ updates key()
ikey_.type = kTypeDeletion;
current_key_.UpdateInternalKey(ikey_.sequence, kTypeDeletion);
// no value associated with delete
value_.clear();
iter_stats_.num_record_drop_user++;
} else if (filter == CompactionFilter::Decision::kPurge) {
// convert the current key to a single delete; key_ is pointing into
// current_key_ at this point, so updating current_key_ updates key()
ikey_.type = kTypeSingleDeletion;
current_key_.UpdateInternalKey(ikey_.sequence, kTypeSingleDeletion);
// no value associated with single delete
value_.clear();
iter_stats_.num_record_drop_user++;
} else if (filter == CompactionFilter::Decision::kChangeValue) {
if (ikey_.type == kTypeBlobIndex) {
// value transfer from blob file to inlined data
ikey_.type = kTypeValue;
current_key_.UpdateInternalKey(ikey_.sequence, ikey_.type);
}
value_ = compaction_filter_value_;
} else if (filter == CompactionFilter::Decision::kRemoveAndSkipUntil) {
*need_skip = true;
compaction_filter_skip_until_.ConvertFromUserKey(kMaxSequenceNumber,
kValueTypeForSeek);
*skip_until = compaction_filter_skip_until_.Encode();
} else if (filter == CompactionFilter::Decision::kChangeBlobIndex) {
// Only the StackableDB-based BlobDB impl's compaction filter should return
// kChangeBlobIndex. Decision about rewriting blob and changing blob index
// in the integrated BlobDB impl is made in subsequent call to
// PrepareOutput() and its callees.
if (!compaction_filter_->IsStackedBlobDbInternalCompactionFilter()) {
status_ = Status::NotSupported(
"Only stacked BlobDB's internal compaction filter can return "
"kChangeBlobIndex.");
validity_info_.Invalidate();
return false;
}
if (ikey_.type == kTypeValue) {
// value transfer from inlined data to blob file
ikey_.type = kTypeBlobIndex;
current_key_.UpdateInternalKey(ikey_.sequence, ikey_.type);
}
value_ = compaction_filter_value_;
} else if (filter == CompactionFilter::Decision::kIOError) {
if (!compaction_filter_->IsStackedBlobDbInternalCompactionFilter()) {
status_ = Status::NotSupported(
"CompactionFilter for integrated BlobDB should not return kIOError");
validity_info_.Invalidate();
return false;
}
status_ = Status::IOError("Failed to access blob during compaction filter");
error = true;
}
return !error;
}
void CompactionIterator::NextFromInput() {
at_next_ = false;
validity_info_.Invalidate();
while (!Valid() && input_.Valid() && !IsPausingManualCompaction() &&
!IsShuttingDown()) {
key_ = input_.key();
value_ = input_.value();
blob_value_.Reset();
iter_stats_.num_input_records++;
Status pik_status = ParseInternalKey(key_, &ikey_, allow_data_in_errors_);
if (!pik_status.ok()) {
iter_stats_.num_input_corrupt_records++;
// If `expect_valid_internal_key_` is false, return the corrupted key
// and let the caller decide what to do with it.
if (expect_valid_internal_key_) {
status_ = pik_status;
return;
}
key_ = current_key_.SetInternalKey(key_);
has_current_user_key_ = false;
current_user_key_sequence_ = kMaxSequenceNumber;
current_user_key_snapshot_ = 0;
validity_info_.SetValid(ValidContext::kParseKeyError);
break;
}
TEST_SYNC_POINT_CALLBACK("CompactionIterator:ProcessKV", &ikey_);
// Update input statistics
if (ikey_.type == kTypeDeletion || ikey_.type == kTypeSingleDeletion ||
ikey_.type == kTypeDeletionWithTimestamp) {
iter_stats_.num_input_deletion_records++;
}
iter_stats_.total_input_raw_key_bytes += key_.size();
iter_stats_.total_input_raw_value_bytes += value_.size();
// If need_skip is true, we should seek the input iterator
// to internal key skip_until and continue from there.
bool need_skip = false;
// Points either into compaction_filter_skip_until_ or into
// merge_helper_->compaction_filter_skip_until_.
Slice skip_until;
bool user_key_equal_without_ts = false;
int cmp_ts = 0;
if (has_current_user_key_) {
user_key_equal_without_ts =
cmp_->EqualWithoutTimestamp(ikey_.user_key, current_user_key_);
// if timestamp_size_ > 0, then curr_ts_ has been initialized by a
// previous key.
cmp_ts = timestamp_size_ ? cmp_->CompareTimestamp(
ExtractTimestampFromUserKey(
ikey_.user_key, timestamp_size_),
curr_ts_)
: 0;
}
// Check whether the user key changed. After this if statement current_key_
// is a copy of the current input key (maybe converted to a delete by the
// compaction filter). ikey_.user_key is pointing to the copy.
if (!has_current_user_key_ || !user_key_equal_without_ts || cmp_ts != 0) {
// First occurrence of this user key
// Copy key for output
key_ = current_key_.SetInternalKey(key_, &ikey_);
int prev_cmp_with_ts_low =
!full_history_ts_low_ ? 0
: curr_ts_.empty()
? 0
: cmp_->CompareTimestamp(curr_ts_, *full_history_ts_low_);
// If timestamp_size_ > 0, then copy from ikey_ to curr_ts_ for the use
// in next iteration to compare with the timestamp of next key.
UpdateTimestampAndCompareWithFullHistoryLow();
// If
// (1) !has_current_user_key_, OR
// (2) timestamp is disabled, OR
// (3) all history will be preserved, OR
// (4) user key (excluding timestamp) is different from previous key, OR
// (5) timestamp is NO older than *full_history_ts_low_, OR
// (6) timestamp is the largest one older than full_history_ts_low_,
// then current_user_key_ must be treated as a different user key.
// This means, if a user key (excluding ts) is the same as the previous
// user key, and its ts is older than *full_history_ts_low_, then we
// consider this key for GC, e.g. it may be dropped if certain conditions
// match.
if (!has_current_user_key_ || !timestamp_size_ || !full_history_ts_low_ ||
!user_key_equal_without_ts || cmp_with_history_ts_low_ >= 0 ||
prev_cmp_with_ts_low >= 0) {
// Initialize for future comparison for rule (A) and etc.
current_user_key_sequence_ = kMaxSequenceNumber;
current_user_key_snapshot_ = 0;
has_current_user_key_ = true;
}
current_user_key_ = ikey_.user_key;
has_outputted_key_ = false;
last_key_seq_zeroed_ = false;
current_key_committed_ = KeyCommitted(ikey_.sequence);
// Apply the compaction filter to the first committed version of the user
// key.
if (current_key_committed_ &&
!InvokeFilterIfNeeded(&need_skip, &skip_until)) {
break;
}
} else {
// Update the current key to reflect the new sequence number/type without
// copying the user key.
// TODO(rven): Compaction filter does not process keys in this path
// Need to have the compaction filter process multiple versions
// if we have versions on both sides of a snapshot
current_key_.UpdateInternalKey(ikey_.sequence, ikey_.type);
key_ = current_key_.GetInternalKey();
ikey_.user_key = current_key_.GetUserKey();
// Note that newer version of a key is ordered before older versions. If a
// newer version of a key is committed, so as the older version. No need
// to query snapshot_checker_ in that case.
if (UNLIKELY(!current_key_committed_)) {
assert(snapshot_checker_ != nullptr);
current_key_committed_ = KeyCommitted(ikey_.sequence);
// Apply the compaction filter to the first committed version of the
// user key.
if (current_key_committed_ &&
!InvokeFilterIfNeeded(&need_skip, &skip_until)) {
break;
}
}
}
if (UNLIKELY(!current_key_committed_)) {
assert(snapshot_checker_ != nullptr);
validity_info_.SetValid(ValidContext::kCurrentKeyUncommitted);
break;
}
// If there are no snapshots, then this kv affect visibility at tip.
// Otherwise, search though all existing snapshots to find the earliest
// snapshot that is affected by this kv.
SequenceNumber last_sequence = current_user_key_sequence_;
current_user_key_sequence_ = ikey_.sequence;
SequenceNumber last_snapshot = current_user_key_snapshot_;
SequenceNumber prev_snapshot = 0; // 0 means no previous snapshot
current_user_key_snapshot_ =
visible_at_tip_
? earliest_snapshot_
: findEarliestVisibleSnapshot(ikey_.sequence, &prev_snapshot);
if (need_skip) {
// This case is handled below.
} else if (clear_and_output_next_key_) {
// In the previous iteration we encountered a single delete that we could
// not compact out. We will keep this Put, but can drop it's data.
// (See Optimization 3, below.)
if (ikey_.type != kTypeValue && ikey_.type != kTypeBlobIndex &&
ikey_.type != kTypeWideColumnEntity) {
ROCKS_LOG_FATAL(info_log_, "Unexpected key %s for compaction output",
ikey_.DebugString(allow_data_in_errors_, true).c_str());
assert(false);
}
if (current_user_key_snapshot_ < last_snapshot) {
ROCKS_LOG_FATAL(info_log_,
"key %s, current_user_key_snapshot_ (%" PRIu64
") < last_snapshot (%" PRIu64 ")",
ikey_.DebugString(allow_data_in_errors_, true).c_str(),
current_user_key_snapshot_, last_snapshot);
assert(false);
}
if (ikey_.type == kTypeBlobIndex || ikey_.type == kTypeWideColumnEntity) {
ikey_.type = kTypeValue;
current_key_.UpdateInternalKey(ikey_.sequence, ikey_.type);
}
value_.clear();
validity_info_.SetValid(ValidContext::kKeepSDAndClearPut);
clear_and_output_next_key_ = false;
} else if (ikey_.type == kTypeSingleDeletion) {
// We can compact out a SingleDelete if:
// 1) We encounter the corresponding PUT -OR- we know that this key
// doesn't appear past this output level
// =AND=
// 2) We've already returned a record in this snapshot -OR-
// there are no earlier earliest_write_conflict_snapshot.
//
// A note about 2) above:
// we try to determine whether there is any earlier write conflict
// checking snapshot by calling DefinitelyInSnapshot() with seq and
// earliest_write_conflict_snapshot as arguments. For write-prepared
// and write-unprepared transactions, if earliest_write_conflict_snapshot
// is evicted from WritePreparedTxnDB::commit_cache, then
// DefinitelyInSnapshot(seq, earliest_write_conflict_snapshot) returns
// false, even if the seq is actually visible within
// earliest_write_conflict_snapshot. Consequently, CompactionIterator
// may try to zero out its sequence number, thus hitting assertion error
// in debug mode or cause incorrect DBIter return result.
// We observe that earliest_write_conflict_snapshot >= earliest_snapshot,
// and the seq zeroing logic depends on
// DefinitelyInSnapshot(seq, earliest_snapshot). Therefore, if we cannot
// determine whether seq is **definitely** in
// earliest_write_conflict_snapshot, then we can additionally check if
// seq is definitely in earliest_snapshot. If the latter holds, then the
// former holds too.
//
// Rule 1 is needed for SingleDelete correctness. Rule 2 is needed to
// allow Transactions to do write-conflict checking (if we compacted away
// all keys, then we wouldn't know that a write happened in this
// snapshot). If there is no earlier snapshot, then we know that there
// are no active transactions that need to know about any writes.
//
// Optimization 3:
// If we encounter a SingleDelete followed by a PUT and Rule 2 is NOT
// true, then we must output a SingleDelete. In this case, we will decide
// to also output the PUT. While we are compacting less by outputting the
// PUT now, hopefully this will lead to better compaction in the future
// when Rule 2 is later true (Ie, We are hoping we can later compact out
// both the SingleDelete and the Put, while we couldn't if we only
// outputted the SingleDelete now).
// In this case, we can save space by removing the PUT's value as it will
// never be read.
//
// Deletes and Merges are not supported on the same key that has a
// SingleDelete as it is not possible to correctly do any partial
// compaction of such a combination of operations. The result of mixing
// those operations for a given key is documented as being undefined. So
// we can choose how to handle such a combinations of operations. We will
// try to compact out as much as we can in these cases.
// We will report counts on these anomalous cases.
//
// Note: If timestamp is enabled, then record will be eligible for
// deletion, only if, along with above conditions (Rule 1 and Rule 2)
// full_history_ts_low_ is specified and timestamp for that key is less
// than *full_history_ts_low_. If it's not eligible for deletion, then we
// will output the SingleDelete. For Optimization 3 also, if
// full_history_ts_low_ is specified and timestamp for the key is less
// than *full_history_ts_low_ then only optimization will be applied.
// The easiest way to process a SingleDelete during iteration is to peek
// ahead at the next key.
const bool is_timestamp_eligible_for_gc =
(timestamp_size_ == 0 ||
(full_history_ts_low_ && cmp_with_history_ts_low_ < 0));
ParsedInternalKey next_ikey;
AdvanceInputIter();
// Check whether the next key exists, is not corrupt, and is the same key
// as the single delete.
if (input_.Valid() &&
ParseInternalKey(input_.key(), &next_ikey, allow_data_in_errors_)
.ok() &&
cmp_->EqualWithoutTimestamp(ikey_.user_key, next_ikey.user_key)) {
#ifndef NDEBUG
const Compaction* c =
compaction_ ? compaction_->real_compaction() : nullptr;
#endif
TEST_SYNC_POINT_CALLBACK(
"CompactionIterator::NextFromInput:SingleDelete:1",
const_cast<Compaction*>(c));
if (last_key_seq_zeroed_) {
++iter_stats_.num_record_drop_hidden;
++iter_stats_.num_record_drop_obsolete;
assert(bottommost_level_);
AdvanceInputIter();
} else if (prev_snapshot == 0 ||
DefinitelyNotInSnapshot(next_ikey.sequence, prev_snapshot)) {
// Check whether the next key belongs to the same snapshot as the
// SingleDelete.
TEST_SYNC_POINT_CALLBACK(
"CompactionIterator::NextFromInput:SingleDelete:2", nullptr);
if (next_ikey.type == kTypeSingleDeletion) {
// We encountered two SingleDeletes for same key in a row. This
// could be due to unexpected user input. If write-(un)prepared
// transaction is used, this could also be due to releasing an old
// snapshot between a Put and its matching SingleDelete.
// Skip the first SingleDelete and let the next iteration decide
// how to handle the second SingleDelete.
// First SingleDelete has been skipped since we already called
// input_.Next().
++iter_stats_.num_record_drop_obsolete;
++iter_stats_.num_single_del_mismatch;
} else if (next_ikey.type == kTypeDeletion) {
std::ostringstream oss;
oss << "Found SD and type: " << static_cast<int>(next_ikey.type)
<< " on the same key, violating the contract "
"of SingleDelete. Check your application to make sure the "
"application does not mix SingleDelete and Delete for "
"the same key. If you are using "
"write-prepared/write-unprepared transactions, and use "
"SingleDelete to delete certain keys, then make sure "
"TransactionDBOptions::rollback_deletion_type_callback is "
"configured properly. Mixing SD and DEL can lead to "
"undefined behaviors";
++iter_stats_.num_record_drop_obsolete;
++iter_stats_.num_single_del_mismatch;
if (enforce_single_del_contracts_) {
ROCKS_LOG_ERROR(info_log_, "%s", oss.str().c_str());
validity_info_.Invalidate();
status_ = Status::Corruption(oss.str());
return;
}
ROCKS_LOG_WARN(info_log_, "%s", oss.str().c_str());
} else if (!is_timestamp_eligible_for_gc) {
// We cannot drop the SingleDelete as timestamp is enabled, and
// timestamp of this key is greater than or equal to
// *full_history_ts_low_. We will output the SingleDelete.
validity_info_.SetValid(ValidContext::kKeepTsHistory);
} else if (has_outputted_key_ ||
DefinitelyInSnapshot(ikey_.sequence,
earliest_write_conflict_snapshot_) ||
(earliest_snapshot_ < earliest_write_conflict_snapshot_ &&
DefinitelyInSnapshot(ikey_.sequence,
earliest_snapshot_))) {
// Found a matching value, we can drop the single delete and the
// value. It is safe to drop both records since we've already
// outputted a key in this snapshot, or there is no earlier
// snapshot (Rule 2 above).
// Note: it doesn't matter whether the second key is a Put or if it
// is an unexpected Merge or Delete. We will compact it out
// either way. We will maintain counts of how many mismatches
// happened
if (next_ikey.type != kTypeValue &&
next_ikey.type != kTypeBlobIndex &&
next_ikey.type != kTypeWideColumnEntity) {
++iter_stats_.num_single_del_mismatch;
}
++iter_stats_.num_record_drop_hidden;
++iter_stats_.num_record_drop_obsolete;
// Already called input_.Next() once. Call it a second time to
// skip past the second key.
AdvanceInputIter();
} else {
// Found a matching value, but we cannot drop both keys since
// there is an earlier snapshot and we need to leave behind a record
// to know that a write happened in this snapshot (Rule 2 above).
// Clear the value and output the SingleDelete. (The value will be
// outputted on the next iteration.)
// Setting valid_ to true will output the current SingleDelete
validity_info_.SetValid(ValidContext::kKeepSDForConflictCheck);
// Set up the Put to be outputted in the next iteration.
// (Optimization 3).
clear_and_output_next_key_ = true;
TEST_SYNC_POINT_CALLBACK(
"CompactionIterator::NextFromInput:KeepSDForWW",
/*arg=*/nullptr);
}
} else {
// We hit the next snapshot without hitting a put, so the iterator
// returns the single delete.
validity_info_.SetValid(ValidContext::kKeepSDForSnapshot);
TEST_SYNC_POINT_CALLBACK(
"CompactionIterator::NextFromInput:SingleDelete:3",
const_cast<Compaction*>(c));
}
} else {
// We are at the end of the input, could not parse the next key, or hit
// a different key. The iterator returns the single delete if the key
// possibly exists beyond the current output level. We set
// has_current_user_key to false so that if the iterator is at the next
// key, we do not compare it again against the previous key at the next
// iteration. If the next key is corrupt, we return before the
// comparison, so the value of has_current_user_key does not matter.
has_current_user_key_ = false;
if (compaction_ != nullptr &&
DefinitelyInSnapshot(ikey_.sequence, earliest_snapshot_) &&
compaction_->KeyNotExistsBeyondOutputLevel(ikey_.user_key,
&level_ptrs_) &&
is_timestamp_eligible_for_gc) {
// Key doesn't exist outside of this range.
// Can compact out this SingleDelete.
++iter_stats_.num_record_drop_obsolete;
++iter_stats_.num_single_del_fallthru;
if (!bottommost_level_) {
++iter_stats_.num_optimized_del_drop_obsolete;
}
} else if (last_key_seq_zeroed_) {
// Skip.
++iter_stats_.num_record_drop_hidden;
++iter_stats_.num_record_drop_obsolete;
assert(bottommost_level_);
} else {
// Output SingleDelete
validity_info_.SetValid(ValidContext::kKeepSD);
}
}
if (Valid()) {
at_next_ = true;
}
} else if (last_snapshot == current_user_key_snapshot_ ||
(last_snapshot > 0 &&
last_snapshot < current_user_key_snapshot_)) {
// If the earliest snapshot is which this key is visible in
// is the same as the visibility of a previous instance of the
// same key, then this kv is not visible in any snapshot.
// Hidden by an newer entry for same user key
//
// Note: Dropping this key will not affect TransactionDB write-conflict
// checking since there has already been a record returned for this key
// in this snapshot.
if (last_sequence < current_user_key_sequence_) {
ROCKS_LOG_FATAL(info_log_,
"key %s, last_sequence (%" PRIu64
") < current_user_key_sequence_ (%" PRIu64 ")",
ikey_.DebugString(allow_data_in_errors_, true).c_str(),
last_sequence, current_user_key_sequence_);
assert(false);
}
++iter_stats_.num_record_drop_hidden; // rule (A)
AdvanceInputIter();
} else if (compaction_ != nullptr &&
(ikey_.type == kTypeDeletion ||
(ikey_.type == kTypeDeletionWithTimestamp &&
cmp_with_history_ts_low_ < 0)) &&
DefinitelyInSnapshot(ikey_.sequence, earliest_snapshot_) &&
compaction_->KeyNotExistsBeyondOutputLevel(ikey_.user_key,
&level_ptrs_)) {
// TODO(noetzli): This is the only place where we use compaction_
// (besides the constructor). We should probably get rid of this
// dependency and find a way to do similar filtering during flushes.
//
// For this user key:
// (1) there is no data in higher levels
// (2) data in lower levels will have larger sequence numbers
// (3) data in layers that are being compacted here and have
// smaller sequence numbers will be dropped in the next
// few iterations of this loop (by rule (A) above).
// Therefore this deletion marker is obsolete and can be dropped.
//
// Note: Dropping this Delete will not affect TransactionDB
// write-conflict checking since it is earlier than any snapshot.
//
// It seems that we can also drop deletion later than earliest snapshot
// given that:
// (1) The deletion is earlier than earliest_write_conflict_snapshot, and
// (2) No value exist earlier than the deletion.
//
// Note also that a deletion marker of type kTypeDeletionWithTimestamp
// will be treated as a different user key unless the timestamp is older
// than *full_history_ts_low_.
++iter_stats_.num_record_drop_obsolete;
if (!bottommost_level_) {
++iter_stats_.num_optimized_del_drop_obsolete;
}
AdvanceInputIter();
} else if ((ikey_.type == kTypeDeletion ||
(ikey_.type == kTypeDeletionWithTimestamp &&
cmp_with_history_ts_low_ < 0)) &&
bottommost_level_) {
// Handle the case where we have a delete key at the bottom most level
// We can skip outputting the key iff there are no subsequent puts for
// this key
assert(!compaction_ || compaction_->KeyNotExistsBeyondOutputLevel(
ikey_.user_key, &level_ptrs_));
ParsedInternalKey next_ikey;
AdvanceInputIter();
#ifndef NDEBUG
const Compaction* c =
compaction_ ? compaction_->real_compaction() : nullptr;
#endif
TEST_SYNC_POINT_CALLBACK(
"CompactionIterator::NextFromInput:BottommostDelete:1",
const_cast<Compaction*>(c));
// Skip over all versions of this key that happen to occur in the same
// snapshot range as the delete.
//
// Note that a deletion marker of type kTypeDeletionWithTimestamp will be
// considered to have a different user key unless the timestamp is older
// than *full_history_ts_low_.
while (!IsPausingManualCompaction() && !IsShuttingDown() &&
input_.Valid() &&
(ParseInternalKey(input_.key(), &next_ikey, allow_data_in_errors_)
.ok()) &&
cmp_->EqualWithoutTimestamp(ikey_.user_key, next_ikey.user_key) &&
(prev_snapshot == 0 ||
DefinitelyNotInSnapshot(next_ikey.sequence, prev_snapshot))) {
AdvanceInputIter();
}
// If you find you still need to output a row with this key, we need to
// output the delete too
if (input_.Valid() &&
(ParseInternalKey(input_.key(), &next_ikey, allow_data_in_errors_)
.ok()) &&
cmp_->EqualWithoutTimestamp(ikey_.user_key, next_ikey.user_key)) {
validity_info_.SetValid(ValidContext::kKeepDel);
at_next_ = true;
}
} else if (ikey_.type == kTypeMerge) {
if (!merge_helper_->HasOperator()) {
status_ = Status::InvalidArgument(
"merge_operator is not properly initialized.");
return;
}
pinned_iters_mgr_.StartPinning();
// We know the merge type entry is not hidden, otherwise we would
// have hit (A)
// We encapsulate the merge related state machine in a different
// object to minimize change to the existing flow.
Status s = merge_helper_->MergeUntil(
&input_, range_del_agg_, prev_snapshot, bottommost_level_,
allow_data_in_errors_, blob_fetcher_.get(), prefetch_buffers_.get(),
&iter_stats_);
merge_out_iter_.SeekToFirst();
if (!s.ok() && !s.IsMergeInProgress()) {
status_ = s;
return;
} else if (merge_out_iter_.Valid()) {
// NOTE: key, value, and ikey_ refer to old entries.
// These will be correctly set below.
key_ = merge_out_iter_.key();
value_ = merge_out_iter_.value();
pik_status = ParseInternalKey(key_, &ikey_, allow_data_in_errors_);
// MergeUntil stops when it encounters a corrupt key and does not
// include them in the result, so we expect the keys here to valid.
if (!pik_status.ok()) {
ROCKS_LOG_FATAL(
info_log_, "Invalid key %s in compaction. %s",
allow_data_in_errors_ ? key_.ToString(true).c_str() : "hidden",
pik_status.getState());
assert(false);
}
// Keep current_key_ in sync.
current_key_.UpdateInternalKey(ikey_.sequence, ikey_.type);
key_ = current_key_.GetInternalKey();
ikey_.user_key = current_key_.GetUserKey();
validity_info_.SetValid(ValidContext::kMerge2);
} else {
// all merge operands were filtered out. reset the user key, since the
// batch consumed by the merge operator should not shadow any keys
// coming after the merges
has_current_user_key_ = false;
pinned_iters_mgr_.ReleasePinnedData();
if (merge_helper_->FilteredUntil(&skip_until)) {
need_skip = true;
}
}
} else {
// 1. new user key -OR-
// 2. different snapshot stripe
// If user-defined timestamp is enabled, we consider keys for GC if they
// are below history_ts_low_. CompactionRangeDelAggregator::ShouldDelete()
// only considers range deletions that are at or below history_ts_low_ and
// trim_ts_. We drop keys here that are below history_ts_low_ and are
// covered by a range tombstone that is at or below history_ts_low_ and
// trim_ts.
bool should_delete = false;
if (!timestamp_size_ || cmp_with_history_ts_low_ < 0) {
should_delete = range_del_agg_->ShouldDelete(
key_, RangeDelPositioningMode::kForwardTraversal);
}
if (should_delete) {
++iter_stats_.num_record_drop_hidden;
++iter_stats_.num_record_drop_range_del;
AdvanceInputIter();
} else {
validity_info_.SetValid(ValidContext::kNewUserKey);
}
}
if (need_skip) {
SkipUntil(skip_until);
}
}
if (!Valid() && IsShuttingDown()) {
status_ = Status::ShutdownInProgress();
}
if (IsPausingManualCompaction()) {
status_ = Status::Incomplete(Status::SubCode::kManualCompactionPaused);
}
// Propagate corruption status from memtable itereator
if (!input_.Valid() && input_.status().IsCorruption()) {
status_ = input_.status();
}
}
bool CompactionIterator::ExtractLargeValueIfNeededImpl() {
if (!blob_file_builder_) {
return false;
}
blob_index_.clear();
const Status s = blob_file_builder_->Add(user_key(), value_, &blob_index_);
if (!s.ok()) {
status_ = s;
validity_info_.Invalidate();
return false;
}
if (blob_index_.empty()) {
return false;
}
value_ = blob_index_;
return true;
}
void CompactionIterator::ExtractLargeValueIfNeeded() {
assert(ikey_.type == kTypeValue);
if (!ExtractLargeValueIfNeededImpl()) {
return;
}
ikey_.type = kTypeBlobIndex;
current_key_.UpdateInternalKey(ikey_.sequence, ikey_.type);
}
void CompactionIterator::GarbageCollectBlobIfNeeded() {
assert(ikey_.type == kTypeBlobIndex);
if (!compaction_) {
return;
}
// GC for integrated BlobDB
if (compaction_->enable_blob_garbage_collection()) {
TEST_SYNC_POINT_CALLBACK(
"CompactionIterator::GarbageCollectBlobIfNeeded::TamperWithBlobIndex",
&value_);
BlobIndex blob_index;
{
const Status s = blob_index.DecodeFrom(value_);
if (!s.ok()) {
status_ = s;
validity_info_.Invalidate();
return;
}
}
if (blob_index.file_number() >=
blob_garbage_collection_cutoff_file_number_) {
return;
}
FilePrefetchBuffer* prefetch_buffer =
prefetch_buffers_ ? prefetch_buffers_->GetOrCreatePrefetchBuffer(
blob_index.file_number())
: nullptr;
uint64_t bytes_read = 0;
{
assert(blob_fetcher_);
const Status s = blob_fetcher_->FetchBlob(
user_key(), blob_index, prefetch_buffer, &blob_value_, &bytes_read);
if (!s.ok()) {
status_ = s;
validity_info_.Invalidate();
return;
}
}
++iter_stats_.num_blobs_read;
iter_stats_.total_blob_bytes_read += bytes_read;
++iter_stats_.num_blobs_relocated;
iter_stats_.total_blob_bytes_relocated += blob_index.size();
value_ = blob_value_;
if (ExtractLargeValueIfNeededImpl()) {
return;
}
ikey_.type = kTypeValue;
current_key_.UpdateInternalKey(ikey_.sequence, ikey_.type);
return;
}
// GC for stacked BlobDB
if (compaction_filter_ &&
compaction_filter_->IsStackedBlobDbInternalCompactionFilter()) {
const auto blob_decision = compaction_filter_->PrepareBlobOutput(
user_key(), value_, &compaction_filter_value_);
if (blob_decision == CompactionFilter::BlobDecision::kCorruption) {
status_ =
Status::Corruption("Corrupted blob reference encountered during GC");
validity_info_.Invalidate();
return;
}
if (blob_decision == CompactionFilter::BlobDecision::kIOError) {
status_ = Status::IOError("Could not relocate blob during GC");
validity_info_.Invalidate();
return;
}
if (blob_decision == CompactionFilter::BlobDecision::kChangeValue) {
value_ = compaction_filter_value_;
return;
}
}
}
void CompactionIterator::DecideOutputLevel() {
assert(compaction_->SupportsPerKeyPlacement());
#ifndef NDEBUG
// Could be overridden by unittest
PerKeyPlacementContext context(level_, ikey_.user_key, value_,
ikey_.sequence);
TEST_SYNC_POINT_CALLBACK("CompactionIterator::PrepareOutput.context",
&context);
output_to_penultimate_level_ = context.output_to_penultimate_level;
#endif /* !NDEBUG */
// if the key is newer than the cutoff sequence or within the earliest
// snapshot, it should output to the penultimate level.
if (ikey_.sequence > preclude_last_level_min_seqno_ ||
ikey_.sequence > earliest_snapshot_) {
output_to_penultimate_level_ = true;
}
if (output_to_penultimate_level_) {
// If it's decided to output to the penultimate level, but unsafe to do so,
// still output to the last level. For example, moving the data from a lower
// level to a higher level outside of the higher-level input key range is
// considered unsafe, because the key may conflict with higher-level SSTs
// not from this compaction.
// TODO: add statistic for declined output_to_penultimate_level
bool safe_to_penultimate_level =
compaction_->WithinPenultimateLevelOutputRange(ikey_.user_key);
if (!safe_to_penultimate_level) {
output_to_penultimate_level_ = false;
// It could happen when disable/enable `last_level_temperature` while
// holding a snapshot. When `last_level_temperature` is not set
// (==kUnknown), the data newer than any snapshot is pushed to the last
// level, but when the per_key_placement feature is enabled on the fly,
// the data later than the snapshot has to be moved to the penultimate
// level, which may or may not be safe. So the user needs to make sure all
// snapshot is released before enabling `last_level_temperature` feature
// We will migrate the feature to `last_level_temperature` and maybe make
// it not dynamically changeable.
if (ikey_.sequence > earliest_snapshot_) {
status_ = Status::Corruption(
"Unsafe to store Seq later than snapshot in the last level if "
"per_key_placement is enabled");
}
}
}
}
void CompactionIterator::PrepareOutput() {
if (Valid()) {
if (ikey_.type == kTypeValue) {
ExtractLargeValueIfNeeded();
} else if (ikey_.type == kTypeBlobIndex) {
GarbageCollectBlobIfNeeded();
}
if (compaction_ != nullptr && compaction_->SupportsPerKeyPlacement()) {
DecideOutputLevel();
}
// Zeroing out the sequence number leads to better compression.
// If this is the bottommost level (no files in lower levels)
// and the earliest snapshot is larger than this seqno
// and the userkey differs from the last userkey in compaction
// then we can squash the seqno to zero.
//
// This is safe for TransactionDB write-conflict checking since transactions
// only care about sequence number larger than any active snapshots.
//
// Can we do the same for levels above bottom level as long as
// KeyNotExistsBeyondOutputLevel() return true?
if (Valid() && compaction_ != nullptr &&
!compaction_->allow_ingest_behind() && bottommost_level_ &&
DefinitelyInSnapshot(ikey_.sequence, earliest_snapshot_) &&
ikey_.type != kTypeMerge && current_key_committed_ &&
!output_to_penultimate_level_ &&
ikey_.sequence < preserve_time_min_seqno_) {
if (ikey_.type == kTypeDeletion ||
(ikey_.type == kTypeSingleDeletion && timestamp_size_ == 0)) {
ROCKS_LOG_FATAL(
info_log_,
"Unexpected key %s for seq-zero optimization. "
"earliest_snapshot %" PRIu64
", earliest_write_conflict_snapshot %" PRIu64
" job_snapshot %" PRIu64
". timestamp_size: %d full_history_ts_low_ %s. validity %x",
ikey_.DebugString(allow_data_in_errors_, true).c_str(),
earliest_snapshot_, earliest_write_conflict_snapshot_,
job_snapshot_, static_cast<int>(timestamp_size_),
full_history_ts_low_ != nullptr
? Slice(*full_history_ts_low_).ToString(true).c_str()
: "null",
validity_info_.rep);
assert(false);
}
ikey_.sequence = 0;
last_key_seq_zeroed_ = true;
TEST_SYNC_POINT_CALLBACK("CompactionIterator::PrepareOutput:ZeroingSeq",
&ikey_);
if (!timestamp_size_) {
current_key_.UpdateInternalKey(0, ikey_.type);
} else if (full_history_ts_low_ && cmp_with_history_ts_low_ < 0) {
// We can also zero out timestamp for better compression.
// For the same user key (excluding timestamp), the timestamp-based
// history can be collapsed to save some space if the timestamp is
// older than *full_history_ts_low_.
const std::string kTsMin(timestamp_size_, static_cast<char>(0));
const Slice ts_slice = kTsMin;
ikey_.SetTimestamp(ts_slice);
current_key_.UpdateInternalKey(0, ikey_.type, &ts_slice);
}
}
}
}
inline SequenceNumber CompactionIterator::findEarliestVisibleSnapshot(
SequenceNumber in, SequenceNumber* prev_snapshot) {
assert(snapshots_->size());
if (snapshots_->size() == 0) {
ROCKS_LOG_FATAL(info_log_,
"No snapshot left in findEarliestVisibleSnapshot");
}
auto snapshots_iter =
std::lower_bound(snapshots_->begin(), snapshots_->end(), in);
assert(prev_snapshot != nullptr);
if (snapshots_iter == snapshots_->begin()) {
*prev_snapshot = 0;
} else {
*prev_snapshot = *std::prev(snapshots_iter);
if (*prev_snapshot >= in) {
ROCKS_LOG_FATAL(info_log_,
"*prev_snapshot (%" PRIu64 ") >= in (%" PRIu64
") in findEarliestVisibleSnapshot",
*prev_snapshot, in);
assert(false);
}
}
if (snapshot_checker_ == nullptr) {
return snapshots_iter != snapshots_->end() ? *snapshots_iter
: kMaxSequenceNumber;
}
bool has_released_snapshot = !released_snapshots_.empty();
for (; snapshots_iter != snapshots_->end(); ++snapshots_iter) {
auto cur = *snapshots_iter;
if (in > cur) {
ROCKS_LOG_FATAL(info_log_,
"in (%" PRIu64 ") > cur (%" PRIu64
") in findEarliestVisibleSnapshot",
in, cur);
assert(false);
}
// Skip if cur is in released_snapshots.
if (has_released_snapshot && released_snapshots_.count(cur) > 0) {
continue;
}
auto res = snapshot_checker_->CheckInSnapshot(in, cur);
if (res == SnapshotCheckerResult::kInSnapshot) {
return cur;
} else if (res == SnapshotCheckerResult::kSnapshotReleased) {
released_snapshots_.insert(cur);
}
*prev_snapshot = cur;
}
return kMaxSequenceNumber;
}
uint64_t CompactionIterator::ComputeBlobGarbageCollectionCutoffFileNumber(
const CompactionProxy* compaction) {
if (!compaction) {
return 0;
}
if (!compaction->enable_blob_garbage_collection()) {
return 0;
}
const Version* const version = compaction->input_version();
assert(version);
const VersionStorageInfo* const storage_info = version->storage_info();
assert(storage_info);
const auto& blob_files = storage_info->GetBlobFiles();
const size_t cutoff_index = static_cast<size_t>(
compaction->blob_garbage_collection_age_cutoff() * blob_files.size());
if (cutoff_index >= blob_files.size()) {
return std::numeric_limits<uint64_t>::max();
}
const auto& meta = blob_files[cutoff_index];
assert(meta);
return meta->GetBlobFileNumber();
}
std::unique_ptr<BlobFetcher> CompactionIterator::CreateBlobFetcherIfNeeded(
const CompactionProxy* compaction) {
if (!compaction) {
return nullptr;
}
const Version* const version = compaction->input_version();
if (!version) {
return nullptr;
}
ReadOptions read_options;
read_options.fill_cache = false;
return std::unique_ptr<BlobFetcher>(new BlobFetcher(version, read_options));
}
std::unique_ptr<PrefetchBufferCollection>
CompactionIterator::CreatePrefetchBufferCollectionIfNeeded(
const CompactionProxy* compaction) {
if (!compaction) {
return nullptr;
}
if (!compaction->input_version()) {
return nullptr;
}
if (compaction->allow_mmap_reads()) {
return nullptr;
}
const uint64_t readahead_size = compaction->blob_compaction_readahead_size();
if (!readahead_size) {
return nullptr;
}
return std::unique_ptr<PrefetchBufferCollection>(
new PrefetchBufferCollection(readahead_size));
}
} // namespace ROCKSDB_NAMESPACE