rocksdb/db/compaction_iterator.cc
Mikhail Antonov 7fe3b32896 Added support for differential snapshots
Summary:
The motivation for this PR is to add to RocksDB support for differential (incremental) snapshots, as snapshot of the DB changes between two points in time (one can think of it as diff between to sequence numbers, or the diff D which can be thought of as an SST file or just set of KVs that can be applied to sequence number S1 to get the database to the state at sequence number S2).

This feature would be useful for various distributed storages layers built on top of RocksDB, as it should help reduce resources (time and network bandwidth) needed to recover and rebuilt DB instances as replicas in the context of distributed storages.

From the API standpoint that would like client app requesting iterator between (start seqnum) and current DB state, and reading the "diff".

This is a very draft PR for initial review in the discussion on the approach, i'm going to rework some parts and keep updating the PR.

For now, what's done here according to initial discussions:

Preserving deletes:
 - We want to be able to optionally preserve recent deletes for some defined period of time, so that if a delete came in recently and might need to be included in the next incremental snapshot it would't get dropped by a compaction. This is done by adding new param to Options (preserve deletes flag) and new variable to DB Impl where we keep track of the sequence number after which we don't want to drop tombstones, even if they are otherwise eligible for deletion.
 - I also added a new API call for clients to be able to advance this cutoff seqnum after which we drop deletes; i assume it's more flexible to let clients control this, since otherwise we'd need to keep some kind of timestamp < -- > seqnum mapping inside the DB, which sounds messy and painful to support. Clients could make use of it by periodically calling GetLatestSequenceNumber(), noting the timestamp, doing some calculation and figuring out by how much we need to advance the cutoff seqnum.
 - Compaction codepath in compaction_iterator.cc has been modified to avoid dropping tombstones with seqnum > cutoff seqnum.

Iterator changes:
 - couple params added to ReadOptions, to optionally allow client to request internal keys instead of user keys (so that client can get the latest value of a key, be it delete marker or a put), as well as min timestamp and min seqnum.

TableCache changes:
 - I modified table_cache code to be able to quickly exclude SST files from iterators heep if creation_time on the file is less then iter_start_ts as passed in ReadOptions. That would help a lot in some DB settings (like reading very recent data only or using FIFO compactions), but not so much for universal compaction with more or less long iterator time span.

What's left:

 - Still looking at how to best plug that inside DBIter codepath. So far it seems that FindNextUserKeyInternal only parses values as UserKeys, and iter->key() call generally returns user key. Can we add new API to DBIter as internal_key(), and modify this internal method to optionally set saved_key_ to point to the full internal key? I don't need to store actual seqnum there, but I do need to store type.
Closes https://github.com/facebook/rocksdb/pull/2999

Differential Revision: D6175602

Pulled By: mikhail-antonov

fbshipit-source-id: c779a6696ee2d574d86c69cec866a3ae095aa900
2017-11-01 18:56:43 -07:00

644 lines
26 KiB
C++

// 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_iterator.h"
#include "db/snapshot_checker.h"
#include "port/likely.h"
#include "rocksdb/listener.h"
#include "table/internal_iterator.h"
namespace rocksdb {
#ifndef ROCKSDB_LITE
CompactionEventListener::CompactionListenerValueType fromInternalValueType(
ValueType vt) {
switch (vt) {
case kTypeDeletion:
return CompactionEventListener::CompactionListenerValueType::kDelete;
case kTypeValue:
return CompactionEventListener::CompactionListenerValueType::kValue;
case kTypeMerge:
return CompactionEventListener::CompactionListenerValueType::
kMergeOperand;
case kTypeSingleDeletion:
return CompactionEventListener::CompactionListenerValueType::
kSingleDelete;
case kTypeRangeDeletion:
return CompactionEventListener::CompactionListenerValueType::kRangeDelete;
case kTypeBlobIndex:
return CompactionEventListener::CompactionListenerValueType::kBlobIndex;
default:
assert(false);
return CompactionEventListener::CompactionListenerValueType::kInvalid;
}
}
#endif // ROCKSDB_LITE
CompactionIterator::CompactionIterator(
InternalIterator* input, const Comparator* cmp, MergeHelper* merge_helper,
SequenceNumber last_sequence, std::vector<SequenceNumber>* snapshots,
SequenceNumber earliest_write_conflict_snapshot,
const SnapshotChecker* snapshot_checker, Env* env,
bool expect_valid_internal_key, RangeDelAggregator* range_del_agg,
const Compaction* compaction, const CompactionFilter* compaction_filter,
CompactionEventListener* compaction_listener,
const std::atomic<bool>* shutting_down,
const SequenceNumber preserve_deletes_seqnum)
: CompactionIterator(
input, cmp, merge_helper, last_sequence, snapshots,
earliest_write_conflict_snapshot, snapshot_checker, env,
expect_valid_internal_key, range_del_agg,
std::unique_ptr<CompactionProxy>(
compaction ? new CompactionProxy(compaction) : nullptr),
compaction_filter, compaction_listener, shutting_down,
preserve_deletes_seqnum) {}
CompactionIterator::CompactionIterator(
InternalIterator* input, const Comparator* cmp, MergeHelper* merge_helper,
SequenceNumber last_sequence, std::vector<SequenceNumber>* snapshots,
SequenceNumber earliest_write_conflict_snapshot,
const SnapshotChecker* snapshot_checker, Env* env,
bool expect_valid_internal_key, RangeDelAggregator* range_del_agg,
std::unique_ptr<CompactionProxy> compaction,
const CompactionFilter* compaction_filter,
CompactionEventListener* compaction_listener,
const std::atomic<bool>* shutting_down,
const SequenceNumber preserve_deletes_seqnum
)
: input_(input),
cmp_(cmp),
merge_helper_(merge_helper),
snapshots_(snapshots),
earliest_write_conflict_snapshot_(earliest_write_conflict_snapshot),
snapshot_checker_(snapshot_checker),
env_(env),
expect_valid_internal_key_(expect_valid_internal_key),
range_del_agg_(range_del_agg),
compaction_(std::move(compaction)),
compaction_filter_(compaction_filter),
#ifndef ROCKSDB_LITE
compaction_listener_(compaction_listener),
#endif // ROCKSDB_LITE
shutting_down_(shutting_down),
preserve_deletes_seqnum_(preserve_deletes_seqnum),
ignore_snapshots_(false),
current_user_key_sequence_(0),
current_user_key_snapshot_(0),
merge_out_iter_(merge_helper_),
current_key_committed_(false) {
assert(compaction_filter_ == nullptr || compaction_ != nullptr);
bottommost_level_ =
compaction_ == nullptr ? false : compaction_->bottommost_level();
if (compaction_ != nullptr) {
level_ptrs_ = std::vector<size_t>(compaction_->number_levels(), 0);
}
if (snapshots_->size() == 0) {
// optimize for fast path if there are no snapshots
visible_at_tip_ = true;
earliest_snapshot_ = kMaxSequenceNumber;
latest_snapshot_ = 0;
} else {
visible_at_tip_ = false;
earliest_snapshot_ = snapshots_->at(0);
latest_snapshot_ = snapshots_->back();
}
if (compaction_filter_ != nullptr) {
if (compaction_filter_->IgnoreSnapshots()) {
ignore_snapshots_ = true;
}
} else {
ignore_snapshots_ = false;
}
input_->SetPinnedItersMgr(&pinned_iters_mgr_);
}
CompactionIterator::~CompactionIterator() {
// input_ Iteartor 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();
bool valid_key __attribute__((__unused__));
valid_key = ParseInternalKey(key_, &ikey_);
// 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.
assert(valid_key);
// Keep current_key_ in sync.
current_key_.UpdateInternalKey(ikey_.sequence, ikey_.type);
key_ = current_key_.GetInternalKey();
ikey_.user_key = current_key_.GetUserKey();
valid_ = true;
} 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_) {
input_->Next();
}
NextFromInput();
}
if (valid_) {
// Record that we've outputted a record for the current key.
has_outputted_key_ = true;
}
PrepareOutput();
}
void CompactionIterator::InvokeFilterIfNeeded(bool* need_skip,
Slice* skip_until) {
if (compaction_filter_ != nullptr && ikey_.type == kTypeValue &&
(visible_at_tip_ || ikey_.sequence > latest_snapshot_ ||
ignore_snapshots_)) {
// 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;
compaction_filter_value_.clear();
compaction_filter_skip_until_.Clear();
{
StopWatchNano timer(env_, true);
filter = compaction_filter_->FilterV2(
compaction_->level(), ikey_.user_key,
CompactionFilter::ValueType::kValue, value_,
&compaction_filter_value_, compaction_filter_skip_until_.rep());
iter_stats_.total_filter_time +=
env_ != nullptr ? timer.ElapsedNanos() : 0;
}
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::kChangeValue) {
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();
}
}
}
void CompactionIterator::NextFromInput() {
at_next_ = false;
valid_ = false;
while (!valid_ && input_->Valid() && !IsShuttingDown()) {
key_ = input_->key();
value_ = input_->value();
iter_stats_.num_input_records++;
if (!ParseInternalKey(key_, &ikey_)) {
// If `expect_valid_internal_key_` is false, return the corrupted key
// and let the caller decide what to do with it.
// TODO(noetzli): We should have a more elegant solution for this.
if (expect_valid_internal_key_) {
assert(!"Corrupted internal key not expected.");
status_ = Status::Corruption("Corrupted internal key not expected.");
break;
}
key_ = current_key_.SetInternalKey(key_);
has_current_user_key_ = false;
current_user_key_sequence_ = kMaxSequenceNumber;
current_user_key_snapshot_ = 0;
iter_stats_.num_input_corrupt_records++;
valid_ = true;
break;
}
// Update input statistics
if (ikey_.type == kTypeDeletion || ikey_.type == kTypeSingleDeletion) {
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;
// 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_ ||
!cmp_->Equal(ikey_.user_key, current_user_key_)) {
// First occurrence of this user key
// Copy key for output
key_ = current_key_.SetInternalKey(key_, &ikey_);
current_user_key_ = ikey_.user_key;
has_current_user_key_ = true;
has_outputted_key_ = false;
current_user_key_sequence_ = kMaxSequenceNumber;
current_user_key_snapshot_ = 0;
current_key_committed_ =
(snapshot_checker_ == nullptr ||
snapshot_checker_->IsInSnapshot(ikey_.sequence, kMaxSequenceNumber));
#ifndef ROCKSDB_LITE
if (compaction_listener_) {
compaction_listener_->OnCompaction(compaction_->level(), ikey_.user_key,
fromInternalValueType(ikey_.type),
value_, ikey_.sequence, true);
}
#endif // !ROCKSDB_LITE
// Apply the compaction filter to the first committed version of the user
// key.
if (current_key_committed_) {
InvokeFilterIfNeeded(&need_skip, &skip_until);
}
} else {
#ifndef ROCKSDB_LITE
if (compaction_listener_) {
compaction_listener_->OnCompaction(compaction_->level(), ikey_.user_key,
fromInternalValueType(ikey_.type),
value_, ikey_.sequence, false);
}
#endif // ROCKSDB_LITE
// 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_ =
snapshot_checker_->IsInSnapshot(ikey_.sequence, kMaxSequenceNumber);
// Apply the compaction filter to the first committed version of the
// user key.
if (current_key_committed_) {
InvokeFilterIfNeeded(&need_skip, &skip_until);
}
}
}
if (UNLIKELY(!current_key_committed_)) {
assert(snapshot_checker_ != nullptr);
valid_ = true;
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 __attribute__((__unused__));
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.)
assert(ikey_.type == kTypeValue);
assert(current_user_key_snapshot_ == last_snapshot);
value_.clear();
valid_ = true;
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.
//
// 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.
// The easiest way to process a SingleDelete during iteration is to peek
// ahead at the next key.
ParsedInternalKey next_ikey;
input_->Next();
// 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) &&
cmp_->Equal(ikey_.user_key, next_ikey.user_key)) {
// Check whether the next key belongs to the same snapshot as the
// SingleDelete.
if (prev_snapshot == 0 || next_ikey.sequence > prev_snapshot) {
if (next_ikey.type == kTypeSingleDeletion) {
// We encountered two SingleDeletes in a row. This could be due to
// unexpected user input.
// 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 ((ikey_.sequence <= earliest_write_conflict_snapshot_) ||
has_outputted_key_) {
// 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) {
++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.
input_->Next();
} 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
valid_ = true;
// Set up the Put to be outputted in the next iteration.
// (Optimization 3).
clear_and_output_next_key_ = true;
}
} else {
// We hit the next snapshot without hitting a put, so the iterator
// returns the single delete.
valid_ = true;
}
} 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 && ikey_.sequence <= earliest_snapshot_ &&
compaction_->KeyNotExistsBeyondOutputLevel(ikey_.user_key,
&level_ptrs_)) {
// 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 {
// Output SingleDelete
valid_ = true;
}
}
if (valid_) {
at_next_ = true;
}
} else if (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
// TODO(noetzli): why not > ?
//
// 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.
assert(last_sequence >= current_user_key_sequence_);
++iter_stats_.num_record_drop_hidden; // (A)
input_->Next();
} else if (compaction_ != nullptr && ikey_.type == kTypeDeletion &&
ikey_.sequence <= earliest_snapshot_ &&
ikeyNotNeededForIncrementalSnapshot() &&
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.
++iter_stats_.num_record_drop_obsolete;
if (!bottommost_level_) {
++iter_stats_.num_optimized_del_drop_obsolete;
}
input_->Next();
} 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_);
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();
bool valid_key __attribute__((__unused__));
valid_key = ParseInternalKey(key_, &ikey_);
// MergeUntil stops when it encounters a corrupt key and does not
// include them in the result, so we expect the keys here to valid.
assert(valid_key);
// Keep current_key_ in sync.
current_key_.UpdateInternalKey(ikey_.sequence, ikey_.type);
key_ = current_key_.GetInternalKey();
ikey_.user_key = current_key_.GetUserKey();
valid_ = true;
} 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
bool should_delete = range_del_agg_->ShouldDelete(
key_, RangeDelAggregator::RangePositioningMode::kForwardTraversal);
if (should_delete) {
++iter_stats_.num_record_drop_hidden;
++iter_stats_.num_record_drop_range_del;
input_->Next();
} else {
valid_ = true;
}
}
if (need_skip) {
input_->Seek(skip_until);
}
}
if (!valid_ && IsShuttingDown()) {
status_ = Status::ShutdownInProgress();
}
}
void CompactionIterator::PrepareOutput() {
// 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.
if ((compaction_ != nullptr &&
!compaction_->allow_ingest_behind()) &&
ikeyNotNeededForIncrementalSnapshot() &&
bottommost_level_ && valid_ && ikey_.sequence <= earliest_snapshot_ &&
(snapshot_checker_ == nullptr || LIKELY(snapshot_checker_->IsInSnapshot(
ikey_.sequence, earliest_snapshot_))) &&
ikey_.type != kTypeMerge &&
!cmp_->Equal(compaction_->GetLargestUserKey(), ikey_.user_key)) {
assert(ikey_.type != kTypeDeletion && ikey_.type != kTypeSingleDeletion);
ikey_.sequence = 0;
current_key_.UpdateInternalKey(0, ikey_.type);
}
}
inline SequenceNumber CompactionIterator::findEarliestVisibleSnapshot(
SequenceNumber in, SequenceNumber* prev_snapshot) {
assert(snapshots_->size());
SequenceNumber prev = kMaxSequenceNumber;
for (const auto cur : *snapshots_) {
assert(prev == kMaxSequenceNumber || prev <= cur);
if (cur >= in && (snapshot_checker_ == nullptr ||
snapshot_checker_->IsInSnapshot(in, cur))) {
*prev_snapshot = prev == kMaxSequenceNumber ? 0 : prev;
return cur;
}
prev = cur;
assert(prev < kMaxSequenceNumber);
}
*prev_snapshot = prev;
return kMaxSequenceNumber;
}
// used in 2 places - prevents deletion markers to be dropped if they may be
// needed and disables seqnum zero-out in PrepareOutput for recent keys.
inline bool CompactionIterator::ikeyNotNeededForIncrementalSnapshot() {
return (!compaction_->preserve_deletes()) ||
(ikey_.sequence < preserve_deletes_seqnum_);
}
} // namespace rocksdb