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rocksdb/utilities/transactions/write_prepared_txn_db.h
Alexander Zinoviev 32a6dd9a41 Add a new CPU time counter to compaction report (#4889) 
Summary:
Measure CPU time consumed for a compaction and report it in the stats report
Enable NowCPUNanos() to work for MacOS
Pull Request resolved: https://github.com/facebook/rocksdb/pull/4889

Differential Revision: D13701276

Pulled By: zinoale

fbshipit-source-id: 5024e5bbccd4dd10fd90d947870237f436445055
2019-01-29 17:24:00 -08:00

874 lines
38 KiB
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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).
#pragma once
#ifndef ROCKSDB_LITE
#ifndef __STDC_FORMAT_MACROS
#define __STDC_FORMAT_MACROS
#endif
#include <inttypes.h>
#include <mutex>
#include <queue>
#include <set>
#include <string>
#include <unordered_map>
#include <vector>
#include "db/db_iter.h"
#include "db/pre_release_callback.h"
#include "db/read_callback.h"
#include "db/snapshot_checker.h"
#include "rocksdb/db.h"
#include "rocksdb/options.h"
#include "rocksdb/utilities/transaction_db.h"
#include "util/set_comparator.h"
#include "util/string_util.h"
#include "utilities/transactions/pessimistic_transaction.h"
#include "utilities/transactions/pessimistic_transaction_db.h"
#include "utilities/transactions/transaction_lock_mgr.h"
#include "utilities/transactions/write_prepared_txn.h"
namespace rocksdb {
#define ROCKS_LOG_DETAILS(LGR, FMT, ...) \
; // due to overhead by default skip such lines
// ROCKS_LOG_DEBUG(LGR, FMT, ##__VA_ARGS__)
// A PessimisticTransactionDB that writes data to DB after prepare phase of 2PC.
// In this way some data in the DB might not be committed. The DB provides
// mechanisms to tell such data apart from committed data.
class WritePreparedTxnDB : public PessimisticTransactionDB {
public:
explicit WritePreparedTxnDB(
DB* db, const TransactionDBOptions& txn_db_options,
size_t snapshot_cache_bits = DEF_SNAPSHOT_CACHE_BITS,
size_t commit_cache_bits = DEF_COMMIT_CACHE_BITS)
: PessimisticTransactionDB(db, txn_db_options),
SNAPSHOT_CACHE_BITS(snapshot_cache_bits),
SNAPSHOT_CACHE_SIZE(static_cast<size_t>(1ull << SNAPSHOT_CACHE_BITS)),
COMMIT_CACHE_BITS(commit_cache_bits),
COMMIT_CACHE_SIZE(static_cast<size_t>(1ull << COMMIT_CACHE_BITS)),
FORMAT(COMMIT_CACHE_BITS) {
Init(txn_db_options);
}
explicit WritePreparedTxnDB(
StackableDB* db, const TransactionDBOptions& txn_db_options,
size_t snapshot_cache_bits = DEF_SNAPSHOT_CACHE_BITS,
size_t commit_cache_bits = DEF_COMMIT_CACHE_BITS)
: PessimisticTransactionDB(db, txn_db_options),
SNAPSHOT_CACHE_BITS(snapshot_cache_bits),
SNAPSHOT_CACHE_SIZE(static_cast<size_t>(1ull << SNAPSHOT_CACHE_BITS)),
COMMIT_CACHE_BITS(commit_cache_bits),
COMMIT_CACHE_SIZE(static_cast<size_t>(1ull << COMMIT_CACHE_BITS)),
FORMAT(COMMIT_CACHE_BITS) {
Init(txn_db_options);
}
virtual ~WritePreparedTxnDB();
virtual Status Initialize(
const std::vector<size_t>& compaction_enabled_cf_indices,
const std::vector<ColumnFamilyHandle*>& handles) override;
Transaction* BeginTransaction(const WriteOptions& write_options,
const TransactionOptions& txn_options,
Transaction* old_txn) override;
// Optimized version of ::Write that receives more optimization request such
// as skip_concurrency_control.
using PessimisticTransactionDB::Write;
Status Write(const WriteOptions& opts, const TransactionDBWriteOptimizations&,
WriteBatch* updates) override;
// Write the batch to the underlying DB and mark it as committed. Could be
// used by both directly from TxnDB or through a transaction.
Status WriteInternal(const WriteOptions& write_options, WriteBatch* batch,
size_t batch_cnt, WritePreparedTxn* txn);
using DB::Get;
virtual Status Get(const ReadOptions& options,
ColumnFamilyHandle* column_family, const Slice& key,
PinnableSlice* value) override;
using DB::MultiGet;
virtual std::vector<Status> MultiGet(
const ReadOptions& options,
const std::vector<ColumnFamilyHandle*>& column_family,
const std::vector<Slice>& keys,
std::vector<std::string>* values) override;
using DB::NewIterator;
virtual Iterator* NewIterator(const ReadOptions& options,
ColumnFamilyHandle* column_family) override;
using DB::NewIterators;
virtual Status NewIterators(
const ReadOptions& options,
const std::vector<ColumnFamilyHandle*>& column_families,
std::vector<Iterator*>* iterators) override;
// Check whether the transaction that wrote the value with sequence number seq
// is visible to the snapshot with sequence number snapshot_seq.
// Returns true if commit_seq <= snapshot_seq
// If the snapshot_seq is already released and snapshot_seq <= max, sets
// *snap_released to true and returns true as well.
inline bool IsInSnapshot(uint64_t prep_seq, uint64_t snapshot_seq,
uint64_t min_uncommitted = 0,
bool* snap_released = nullptr) const {
ROCKS_LOG_DETAILS(info_log_,
"IsInSnapshot %" PRIu64 " in %" PRIu64
" min_uncommitted %" PRIu64,
prep_seq, snapshot_seq, min_uncommitted);
// Caller is responsible to initialize snap_released.
assert(snap_released == nullptr || *snap_released == false);
// Here we try to infer the return value without looking into prepare list.
// This would help avoiding synchronization over a shared map.
// TODO(myabandeh): optimize this. This sequence of checks must be correct
// but not necessary efficient
if (prep_seq == 0) {
// Compaction will output keys to bottom-level with sequence number 0 if
// it is visible to the earliest snapshot.
ROCKS_LOG_DETAILS(
info_log_, "IsInSnapshot %" PRIu64 " in %" PRIu64 " returns %" PRId32,
prep_seq, snapshot_seq, 1);
return true;
}
if (snapshot_seq < prep_seq) {
// snapshot_seq < prep_seq <= commit_seq => snapshot_seq < commit_seq
ROCKS_LOG_DETAILS(
info_log_, "IsInSnapshot %" PRIu64 " in %" PRIu64 " returns %" PRId32,
prep_seq, snapshot_seq, 0);
return false;
}
if (prep_seq < min_uncommitted) {
ROCKS_LOG_DETAILS(info_log_,
"IsInSnapshot %" PRIu64 " in %" PRIu64
" returns %" PRId32
" because of min_uncommitted %" PRIu64,
prep_seq, snapshot_seq, 1, min_uncommitted);
return true;
}
auto indexed_seq = prep_seq % COMMIT_CACHE_SIZE;
CommitEntry64b dont_care;
CommitEntry cached;
bool exist = GetCommitEntry(indexed_seq, &dont_care, &cached);
if (exist && prep_seq == cached.prep_seq) {
// It is committed and also not evicted from commit cache
ROCKS_LOG_DETAILS(
info_log_, "IsInSnapshot %" PRIu64 " in %" PRIu64 " returns %" PRId32,
prep_seq, snapshot_seq, cached.commit_seq <= snapshot_seq);
return cached.commit_seq <= snapshot_seq;
}
// else it could be committed but not inserted in the map which could happen
// after recovery, or it could be committed and evicted by another commit,
// or never committed.
// At this point we dont know if it was committed or it is still prepared
auto max_evicted_seq = max_evicted_seq_.load(std::memory_order_acquire);
// max_evicted_seq_ when we did GetCommitEntry <= max_evicted_seq now
if (max_evicted_seq < prep_seq) {
// Not evicted from cache and also not present, so must be still prepared
ROCKS_LOG_DETAILS(
info_log_, "IsInSnapshot %" PRIu64 " in %" PRIu64 " returns %" PRId32,
prep_seq, snapshot_seq, 0);
return false;
}
if (!delayed_prepared_empty_.load(std::memory_order_acquire)) {
// We should not normally reach here
WPRecordTick(TXN_PREPARE_MUTEX_OVERHEAD);
ReadLock rl(&prepared_mutex_);
ROCKS_LOG_WARN(info_log_, "prepared_mutex_ overhead %" PRIu64,
static_cast<uint64_t>(delayed_prepared_.size()));
if (delayed_prepared_.find(prep_seq) != delayed_prepared_.end()) {
// This is the order: 1) delayed_prepared_commits_ update, 2) publish 3)
// delayed_prepared_ clean up. So check if it is the case of a late
// clenaup.
auto it = delayed_prepared_commits_.find(prep_seq);
if (it == delayed_prepared_commits_.end()) {
// Then it is not committed yet
ROCKS_LOG_DETAILS(info_log_,
"IsInSnapshot %" PRIu64 " in %" PRIu64
" returns %" PRId32,
prep_seq, snapshot_seq, 0);
return false;
} else {
ROCKS_LOG_DETAILS(info_log_,
"IsInSnapshot %" PRIu64 " in %" PRIu64
" commit: %" PRIu64 " returns %" PRId32,
prep_seq, snapshot_seq, it->second,
snapshot_seq <= it->second);
return it->second <= snapshot_seq;
}
}
}
// When advancing max_evicted_seq_, we move older entires from prepared to
// delayed_prepared_. Also we move evicted entries from commit cache to
// old_commit_map_ if it overlaps with any snapshot. Since prep_seq <=
// max_evicted_seq_, we have three cases: i) in delayed_prepared_, ii) in
// old_commit_map_, iii) committed with no conflict with any snapshot. Case
// (i) delayed_prepared_ is checked above
if (max_evicted_seq < snapshot_seq) { // then (ii) cannot be the case
// only (iii) is the case: committed
// commit_seq <= max_evicted_seq_ < snapshot_seq => commit_seq <
// snapshot_seq
ROCKS_LOG_DETAILS(
info_log_, "IsInSnapshot %" PRIu64 " in %" PRIu64 " returns %" PRId32,
prep_seq, snapshot_seq, 1);
return true;
}
// else (ii) might be the case: check the commit data saved for this
// snapshot. If there was no overlapping commit entry, then it is committed
// with a commit_seq lower than any live snapshot, including snapshot_seq.
if (old_commit_map_empty_.load(std::memory_order_acquire)) {
ROCKS_LOG_DETAILS(info_log_,
"IsInSnapshot %" PRIu64 " in %" PRIu64
" returns %" PRId32 " released=1",
prep_seq, snapshot_seq, 0);
assert(snap_released);
// This snapshot is not valid anymore. We cannot tell if prep_seq is
// committed before or after the snapshot. Return true but also set
// snap_released to true.
*snap_released = true;
return true;
}
{
// We should not normally reach here unless sapshot_seq is old. This is a
// rare case and it is ok to pay the cost of mutex ReadLock for such old,
// reading transactions.
WPRecordTick(TXN_OLD_COMMIT_MAP_MUTEX_OVERHEAD);
ReadLock rl(&old_commit_map_mutex_);
auto prep_set_entry = old_commit_map_.find(snapshot_seq);
bool found = prep_set_entry != old_commit_map_.end();
if (found) {
auto& vec = prep_set_entry->second;
found = std::binary_search(vec.begin(), vec.end(), prep_seq);
} else {
// coming from compaction
ROCKS_LOG_DETAILS(info_log_,
"IsInSnapshot %" PRIu64 " in %" PRIu64
" returns %" PRId32 " released=1",
prep_seq, snapshot_seq, 0);
// This snapshot is not valid anymore. We cannot tell if prep_seq is
// committed before or after the snapshot. Return true but also set
// snap_released to true.
assert(snap_released);
*snap_released = true;
return true;
}
if (!found) {
ROCKS_LOG_DETAILS(info_log_,
"IsInSnapshot %" PRIu64 " in %" PRIu64
" returns %" PRId32,
prep_seq, snapshot_seq, 1);
return true;
}
}
// (ii) it the case: it is committed but after the snapshot_seq
ROCKS_LOG_DETAILS(
info_log_, "IsInSnapshot %" PRIu64 " in %" PRIu64 " returns %" PRId32,
prep_seq, snapshot_seq, 0);
return false;
}
// Add the transaction with prepare sequence seq to the prepared list
void AddPrepared(uint64_t seq);
// Remove the transaction with prepare sequence seq from the prepared list
void RemovePrepared(const uint64_t seq, const size_t batch_cnt = 1);
// Add the transaction with prepare sequence prepare_seq and comtit sequence
// commit_seq to the commit map. loop_cnt is to detect infinite loops.
void AddCommitted(uint64_t prepare_seq, uint64_t commit_seq,
uint8_t loop_cnt = 0);
struct CommitEntry {
uint64_t prep_seq;
uint64_t commit_seq;
CommitEntry() : prep_seq(0), commit_seq(0) {}
CommitEntry(uint64_t ps, uint64_t cs) : prep_seq(ps), commit_seq(cs) {}
bool operator==(const CommitEntry& rhs) const {
return prep_seq == rhs.prep_seq && commit_seq == rhs.commit_seq;
}
};
struct CommitEntry64bFormat {
explicit CommitEntry64bFormat(size_t index_bits)
: INDEX_BITS(index_bits),
PREP_BITS(static_cast<size_t>(64 - PAD_BITS - INDEX_BITS)),
COMMIT_BITS(static_cast<size_t>(64 - PREP_BITS)),
COMMIT_FILTER(static_cast<uint64_t>((1ull << COMMIT_BITS) - 1)),
DELTA_UPPERBOUND(static_cast<uint64_t>((1ull << COMMIT_BITS))) {}
// Number of higher bits of a sequence number that is not used. They are
// used to encode the value type, ...
const size_t PAD_BITS = static_cast<size_t>(8);
// Number of lower bits from prepare seq that can be skipped as they are
// implied by the index of the entry in the array
const size_t INDEX_BITS;
// Number of bits we use to encode the prepare seq
const size_t PREP_BITS;
// Number of bits we use to encode the commit seq.
const size_t COMMIT_BITS;
// Filter to encode/decode commit seq
const uint64_t COMMIT_FILTER;
// The value of commit_seq - prepare_seq + 1 must be less than this bound
const uint64_t DELTA_UPPERBOUND;
};
// Prepare Seq (64 bits) = PAD ... PAD PREP PREP ... PREP INDEX INDEX ...
// INDEX Delta Seq (64 bits) = 0 0 0 0 0 0 0 0 0 0 0 0 DELTA DELTA ...
// DELTA DELTA Encoded Value = PREP PREP .... PREP PREP DELTA DELTA
// ... DELTA DELTA PAD: first bits of a seq that is reserved for tagging and
// hence ignored PREP/INDEX: the used bits in a prepare seq number INDEX: the
// bits that do not have to be encoded (will be provided externally) DELTA:
// prep seq - commit seq + 1 Number of DELTA bits should be equal to number of
// index bits + PADs
struct CommitEntry64b {
constexpr CommitEntry64b() noexcept : rep_(0) {}
CommitEntry64b(const CommitEntry& entry, const CommitEntry64bFormat& format)
: CommitEntry64b(entry.prep_seq, entry.commit_seq, format) {}
CommitEntry64b(const uint64_t ps, const uint64_t cs,
const CommitEntry64bFormat& format) {
assert(ps < static_cast<uint64_t>(
(1ull << (format.PREP_BITS + format.INDEX_BITS))));
assert(ps <= cs);
uint64_t delta = cs - ps + 1; // make initialized delta always >= 1
// zero is reserved for uninitialized entries
assert(0 < delta);
assert(delta < format.DELTA_UPPERBOUND);
if (delta >= format.DELTA_UPPERBOUND) {
throw std::runtime_error(
"commit_seq >> prepare_seq. The allowed distance is " +
ToString(format.DELTA_UPPERBOUND) + " commit_seq is " +
ToString(cs) + " prepare_seq is " + ToString(ps));
}
rep_ = (ps << format.PAD_BITS) & ~format.COMMIT_FILTER;
rep_ = rep_ | delta;
}
// Return false if the entry is empty
bool Parse(const uint64_t indexed_seq, CommitEntry* entry,
const CommitEntry64bFormat& format) {
uint64_t delta = rep_ & format.COMMIT_FILTER;
// zero is reserved for uninitialized entries
assert(delta < static_cast<uint64_t>((1ull << format.COMMIT_BITS)));
if (delta == 0) {
return false; // initialized entry would have non-zero delta
}
assert(indexed_seq < static_cast<uint64_t>((1ull << format.INDEX_BITS)));
uint64_t prep_up = rep_ & ~format.COMMIT_FILTER;
prep_up >>= format.PAD_BITS;
const uint64_t& prep_low = indexed_seq;
entry->prep_seq = prep_up | prep_low;
entry->commit_seq = entry->prep_seq + delta - 1;
return true;
}
private:
uint64_t rep_;
};
// Struct to hold ownership of snapshot and read callback for cleanup.
struct IteratorState;
std::shared_ptr<std::map<uint32_t, const Comparator*>> GetCFComparatorMap() {
return cf_map_;
}
std::shared_ptr<std::map<uint32_t, ColumnFamilyHandle*>> GetCFHandleMap() {
return handle_map_;
}
void UpdateCFComparatorMap(
const std::vector<ColumnFamilyHandle*>& handles) override;
void UpdateCFComparatorMap(ColumnFamilyHandle* handle) override;
virtual const Snapshot* GetSnapshot() override;
SnapshotImpl* GetSnapshotInternal(bool for_ww_conflict_check);
protected:
virtual Status VerifyCFOptions(
const ColumnFamilyOptions& cf_options) override;
private:
friend class WritePreparedCommitEntryPreReleaseCallback;
friend class WritePreparedTransactionTest_IsInSnapshotTest_Test;
friend class WritePreparedTransactionTest_CheckAgainstSnapshotsTest_Test;
friend class WritePreparedTransactionTest_CommitMapTest_Test;
friend class
WritePreparedTransactionTest_ConflictDetectionAfterRecoveryTest_Test;
friend class SnapshotConcurrentAccessTest_SnapshotConcurrentAccessTest_Test;
friend class WritePreparedTransactionTestBase;
friend class PreparedHeap_BasicsTest_Test;
friend class PreparedHeap_EmptyAtTheEnd_Test;
friend class PreparedHeap_Concurrent_Test;
friend class WritePreparedTxn;
friend class WritePreparedTxnDBMock;
friend class WritePreparedTransactionTest_AdvanceMaxEvictedSeqBasicTest_Test;
friend class
WritePreparedTransactionTest_AdvanceMaxEvictedSeqWithDuplicatesTest_Test;
friend class WritePreparedTransactionTest_AdvanceSeqByOne_Test;
friend class WritePreparedTransactionTest_BasicRecoveryTest_Test;
friend class WritePreparedTransactionTest_DoubleSnapshot_Test;
friend class WritePreparedTransactionTest_IsInSnapshotEmptyMapTest_Test;
friend class WritePreparedTransactionTest_IsInSnapshotReleased_Test;
friend class WritePreparedTransactionTest_NewSnapshotLargerThanMax_Test;
friend class WritePreparedTransactionTest_MaxCatchupWithNewSnapshot_Test;
friend class WritePreparedTransactionTest_OldCommitMapGC_Test;
friend class WritePreparedTransactionTest_RollbackTest_Test;
friend class WriteUnpreparedTxnDB;
friend class WriteUnpreparedTransactionTest_RecoveryTest_Test;
void Init(const TransactionDBOptions& /* unused */);
void WPRecordTick(uint32_t ticker_type) const {
RecordTick(db_impl_->immutable_db_options_.statistics.get(), ticker_type);
}
// A heap with the amortized O(1) complexity for erase. It uses one extra heap
// to keep track of erased entries that are not yet on top of the main heap.
class PreparedHeap {
std::priority_queue<uint64_t, std::vector<uint64_t>, std::greater<uint64_t>>
heap_;
std::priority_queue<uint64_t, std::vector<uint64_t>, std::greater<uint64_t>>
erased_heap_;
// True when testing crash recovery
bool TEST_CRASH_ = false;
friend class WritePreparedTxnDB;
public:
~PreparedHeap() {
if (!TEST_CRASH_) {
assert(heap_.empty());
assert(erased_heap_.empty());
}
}
bool empty() { return heap_.empty(); }
uint64_t top() { return heap_.top(); }
void push(uint64_t v) { heap_.push(v); }
void pop() {
heap_.pop();
while (!heap_.empty() && !erased_heap_.empty() &&
// heap_.top() > erased_heap_.top() could happen if we have erased
// a non-existent entry. Ideally the user should not do that but we
// should be resilient against it.
heap_.top() >= erased_heap_.top()) {
if (heap_.top() == erased_heap_.top()) {
heap_.pop();
}
uint64_t erased __attribute__((__unused__));
erased = erased_heap_.top();
erased_heap_.pop();
// No duplicate prepare sequence numbers
assert(erased_heap_.empty() || erased_heap_.top() != erased);
}
while (heap_.empty() && !erased_heap_.empty()) {
erased_heap_.pop();
}
}
void erase(uint64_t seq) {
if (!heap_.empty()) {
if (seq < heap_.top()) {
// Already popped, ignore it.
} else if (heap_.top() == seq) {
pop();
assert(heap_.empty() || heap_.top() != seq);
} else { // (heap_.top() > seq)
// Down the heap, remember to pop it later
erased_heap_.push(seq);
}
}
}
};
void TEST_Crash() override { prepared_txns_.TEST_CRASH_ = true; }
// Get the commit entry with index indexed_seq from the commit table. It
// returns true if such entry exists.
bool GetCommitEntry(const uint64_t indexed_seq, CommitEntry64b* entry_64b,
CommitEntry* entry) const;
// Rewrite the entry with the index indexed_seq in the commit table with the
// commit entry <prep_seq, commit_seq>. If the rewrite results into eviction,
// sets the evicted_entry and returns true.
bool AddCommitEntry(const uint64_t indexed_seq, const CommitEntry& new_entry,
CommitEntry* evicted_entry);
// Rewrite the entry with the index indexed_seq in the commit table with the
// commit entry new_entry only if the existing entry matches the
// expected_entry. Returns false otherwise.
bool ExchangeCommitEntry(const uint64_t indexed_seq,
CommitEntry64b& expected_entry,
const CommitEntry& new_entry);
// Increase max_evicted_seq_ from the previous value prev_max to the new
// value. This also involves taking care of prepared txns that are not
// committed before new_max, as well as updating the list of live snapshots at
// the time of updating the max. Thread-safety: this function can be called
// concurrently. The concurrent invocations of this function is equivalent to
// a serial invocation in which the last invocation is the one with the
// largest new_max value.
void AdvanceMaxEvictedSeq(const SequenceNumber& prev_max,
const SequenceNumber& new_max);
inline SequenceNumber SmallestUnCommittedSeq() {
// Since we update the prepare_heap always from the main write queue via
// PreReleaseCallback, the prepared_txns_.top() indicates the smallest
// prepared data in 2pc transactions. For non-2pc transactions that are
// written in two steps, we also update prepared_txns_ at the first step
// (via the same mechanism) so that their uncommitted data is reflected in
// SmallestUnCommittedSeq.
ReadLock rl(&prepared_mutex_);
// Since we are holding the mutex, and GetLatestSequenceNumber is updated
// after prepared_txns_ are, the value of GetLatestSequenceNumber would
// reflect any uncommitted data that is not added to prepared_txns_ yet.
// Otherwise, if there is no concurrent txn, this value simply reflects that
// latest value in the memtable.
if (!delayed_prepared_.empty()) {
assert(!delayed_prepared_empty_.load());
return *delayed_prepared_.begin();
}
if (prepared_txns_.empty()) {
return db_impl_->GetLatestSequenceNumber() + 1;
} else {
return std::min(prepared_txns_.top(),
db_impl_->GetLatestSequenceNumber() + 1);
}
}
// Enhance the snapshot object by recording in it the smallest uncommitted seq
inline void EnhanceSnapshot(SnapshotImpl* snapshot,
SequenceNumber min_uncommitted) {
assert(snapshot);
snapshot->min_uncommitted_ = min_uncommitted;
}
virtual const std::vector<SequenceNumber> GetSnapshotListFromDB(
SequenceNumber max);
// Will be called by the public ReleaseSnapshot method. Does the maintenance
// internal to WritePreparedTxnDB
void ReleaseSnapshotInternal(const SequenceNumber snap_seq);
// Update the list of snapshots corresponding to the soon-to-be-updated
// max_evicted_seq_. Thread-safety: this function can be called concurrently.
// The concurrent invocations of this function is equivalent to a serial
// invocation in which the last invocation is the one with the largest
// version value.
void UpdateSnapshots(const std::vector<SequenceNumber>& snapshots,
const SequenceNumber& version);
// Check the new list of new snapshots against the old one to see if any of
// the snapshots are released and to do the cleanup for the released snapshot.
void CleanupReleasedSnapshots(
const std::vector<SequenceNumber>& new_snapshots,
const std::vector<SequenceNumber>& old_snapshots);
// Check an evicted entry against live snapshots to see if it should be kept
// around or it can be safely discarded (and hence assume committed for all
// snapshots). Thread-safety: this function can be called concurrently. If it
// is called concurrently with multiple UpdateSnapshots, the result is the
// same as checking the intersection of the snapshot list before updates with
// the snapshot list of all the concurrent updates.
void CheckAgainstSnapshots(const CommitEntry& evicted);
// Add a new entry to old_commit_map_ if prep_seq <= snapshot_seq <
// commit_seq. Return false if checking the next snapshot(s) is not needed.
// This is the case if none of the next snapshots could satisfy the condition.
// next_is_larger: the next snapshot will be a larger value
bool MaybeUpdateOldCommitMap(const uint64_t& prep_seq,
const uint64_t& commit_seq,
const uint64_t& snapshot_seq,
const bool next_is_larger);
// A trick to increase the last visible sequence number by one and also wait
// for the in-flight commits to be visible.
void AdvanceSeqByOne();
// The list of live snapshots at the last time that max_evicted_seq_ advanced.
// The list stored into two data structures: in snapshot_cache_ that is
// efficient for concurrent reads, and in snapshots_ if the data does not fit
// into snapshot_cache_. The total number of snapshots in the two lists
std::atomic<size_t> snapshots_total_ = {};
// The list sorted in ascending order. Thread-safety for writes is provided
// with snapshots_mutex_ and concurrent reads are safe due to std::atomic for
// each entry. In x86_64 architecture such reads are compiled to simple read
// instructions. 128 entries
static const size_t DEF_SNAPSHOT_CACHE_BITS = static_cast<size_t>(7);
const size_t SNAPSHOT_CACHE_BITS;
const size_t SNAPSHOT_CACHE_SIZE;
std::unique_ptr<std::atomic<SequenceNumber>[]> snapshot_cache_;
// 2nd list for storing snapshots. The list sorted in ascending order.
// Thread-safety is provided with snapshots_mutex_.
std::vector<SequenceNumber> snapshots_;
// The list of all snapshots: snapshots_ + snapshot_cache_. This list although
// redundant but simplifies CleanupOldSnapshots implementation.
// Thread-safety is provided with snapshots_mutex_.
std::vector<SequenceNumber> snapshots_all_;
// The version of the latest list of snapshots. This can be used to avoid
// rewriting a list that is concurrently updated with a more recent version.
SequenceNumber snapshots_version_ = 0;
// A heap of prepared transactions. Thread-safety is provided with
// prepared_mutex_.
PreparedHeap prepared_txns_;
// 8m entry, 64MB size
static const size_t DEF_COMMIT_CACHE_BITS = static_cast<size_t>(23);
const size_t COMMIT_CACHE_BITS;
const size_t COMMIT_CACHE_SIZE;
const CommitEntry64bFormat FORMAT;
// commit_cache_ must be initialized to zero to tell apart an empty index from
// a filled one. Thread-safety is provided with commit_cache_mutex_.
std::unique_ptr<std::atomic<CommitEntry64b>[]> commit_cache_;
// The largest evicted *commit* sequence number from the commit_cache_. If a
// seq is smaller than max_evicted_seq_ is might or might not be present in
// commit_cache_. So commit_cache_ must first be checked before consulting
// with max_evicted_seq_.
std::atomic<uint64_t> max_evicted_seq_ = {};
// Order: 1) update future_max_evicted_seq_ = new_max, 2)
// GetSnapshotListFromDB(new_max), max_evicted_seq_ = new_max. Since
// GetSnapshotInternal guarantess that the snapshot seq is larger than
// future_max_evicted_seq_, this guarantes that if a snapshot is not larger
// than max has already being looked at via a GetSnapshotListFromDB(new_max).
std::atomic<uint64_t> future_max_evicted_seq_ = {};
// Advance max_evicted_seq_ by this value each time it needs an update. The
// larger the value, the less frequent advances we would have. We do not want
// it to be too large either as it would cause stalls by doing too much
// maintenance work under the lock.
size_t INC_STEP_FOR_MAX_EVICTED = 1;
// A map from old snapshots (expected to be used by a few read-only txns) to
// prepared sequence number of the evicted entries from commit_cache_ that
// overlaps with such snapshot. These are the prepared sequence numbers that
// the snapshot, to which they are mapped, cannot assume to be committed just
// because it is no longer in the commit_cache_. The vector must be sorted
// after each update.
// Thread-safety is provided with old_commit_map_mutex_.
std::map<SequenceNumber, std::vector<SequenceNumber>> old_commit_map_;
// A set of long-running prepared transactions that are not finished by the
// time max_evicted_seq_ advances their sequence number. This is expected to
// be empty normally. Thread-safety is provided with prepared_mutex_.
std::set<uint64_t> delayed_prepared_;
// Commit of a delayed prepared: 1) update commit cache, 2) update
// delayed_prepared_commits_, 3) publish seq, 3) clean up delayed_prepared_.
// delayed_prepared_commits_ will help us tell apart the unprepared txns from
// the ones that are committed but not cleaned up yet.
std::unordered_map<SequenceNumber, SequenceNumber> delayed_prepared_commits_;
// Update when delayed_prepared_.empty() changes. Expected to be true
// normally.
std::atomic<bool> delayed_prepared_empty_ = {true};
// Update when old_commit_map_.empty() changes. Expected to be true normally.
std::atomic<bool> old_commit_map_empty_ = {true};
mutable port::RWMutex prepared_mutex_;
mutable port::RWMutex old_commit_map_mutex_;
mutable port::RWMutex commit_cache_mutex_;
mutable port::RWMutex snapshots_mutex_;
// A cache of the cf comparators
// Thread safety: since it is a const it is safe to read it concurrently
std::shared_ptr<std::map<uint32_t, const Comparator*>> cf_map_;
// A cache of the cf handles
// Thread safety: since the handle is read-only object it is a const it is
// safe to read it concurrently
std::shared_ptr<std::map<uint32_t, ColumnFamilyHandle*>> handle_map_;
};
class WritePreparedTxnReadCallback : public ReadCallback {
public:
WritePreparedTxnReadCallback(WritePreparedTxnDB* db, SequenceNumber snapshot,
SequenceNumber min_uncommitted)
: db_(db), snapshot_(snapshot), min_uncommitted_(min_uncommitted) {}
// Will be called to see if the seq number visible; if not it moves on to
// the next seq number.
inline virtual bool IsVisible(SequenceNumber seq) override {
return db_->IsInSnapshot(seq, snapshot_, min_uncommitted_);
}
private:
WritePreparedTxnDB* db_;
SequenceNumber snapshot_;
SequenceNumber min_uncommitted_;
};
class AddPreparedCallback : public PreReleaseCallback {
public:
AddPreparedCallback(WritePreparedTxnDB* db, size_t sub_batch_cnt,
bool two_write_queues)
: db_(db),
sub_batch_cnt_(sub_batch_cnt),
two_write_queues_(two_write_queues) {
(void)two_write_queues_; // to silence unused private field warning
}
virtual Status Callback(SequenceNumber prepare_seq,
bool is_mem_disabled) override {
#ifdef NDEBUG
(void)is_mem_disabled;
#endif
assert(!two_write_queues_ || !is_mem_disabled); // implies the 1st queue
for (size_t i = 0; i < sub_batch_cnt_; i++) {
db_->AddPrepared(prepare_seq + i);
}
return Status::OK();
}
private:
WritePreparedTxnDB* db_;
size_t sub_batch_cnt_;
bool two_write_queues_;
};
class WritePreparedCommitEntryPreReleaseCallback : public PreReleaseCallback {
public:
// includes_data indicates that the commit also writes non-empty
// CommitTimeWriteBatch to memtable, which needs to be committed separately.
WritePreparedCommitEntryPreReleaseCallback(WritePreparedTxnDB* db,
DBImpl* db_impl,
SequenceNumber prep_seq,
size_t prep_batch_cnt,
size_t data_batch_cnt = 0,
bool publish_seq = true)
: db_(db),
db_impl_(db_impl),
prep_seq_(prep_seq),
prep_batch_cnt_(prep_batch_cnt),
data_batch_cnt_(data_batch_cnt),
includes_data_(data_batch_cnt_ > 0),
publish_seq_(publish_seq) {
assert((prep_batch_cnt_ > 0) != (prep_seq == kMaxSequenceNumber)); // xor
assert(prep_batch_cnt_ > 0 || data_batch_cnt_ > 0);
}
virtual Status Callback(SequenceNumber commit_seq,
bool is_mem_disabled) override {
#ifdef NDEBUG
(void)is_mem_disabled;
#endif
assert(includes_data_ || prep_seq_ != kMaxSequenceNumber);
const uint64_t last_commit_seq = LIKELY(data_batch_cnt_ <= 1)
? commit_seq
: commit_seq + data_batch_cnt_ - 1;
if (prep_seq_ != kMaxSequenceNumber) {
for (size_t i = 0; i < prep_batch_cnt_; i++) {
db_->AddCommitted(prep_seq_ + i, last_commit_seq);
}
} // else there was no prepare phase
if (includes_data_) {
assert(data_batch_cnt_);
// Commit the data that is accompanied with the commit request
for (size_t i = 0; i < data_batch_cnt_; i++) {
// For commit seq of each batch use the commit seq of the last batch.
// This would make debugging easier by having all the batches having
// the same sequence number.
db_->AddCommitted(commit_seq + i, last_commit_seq);
}
}
if (db_impl_->immutable_db_options().two_write_queues && publish_seq_) {
assert(is_mem_disabled); // implies the 2nd queue
// Publish the sequence number. We can do that here assuming the callback
// is invoked only from one write queue, which would guarantee that the
// publish sequence numbers will be in order, i.e., once a seq is
// published all the seq prior to that are also publishable.
db_impl_->SetLastPublishedSequence(last_commit_seq);
}
// else SequenceNumber that is updated as part of the write already does the
// publishing
return Status::OK();
}
private:
WritePreparedTxnDB* db_;
DBImpl* db_impl_;
// kMaxSequenceNumber if there was no prepare phase
SequenceNumber prep_seq_;
size_t prep_batch_cnt_;
size_t data_batch_cnt_;
// Either because it is commit without prepare or it has a
// CommitTimeWriteBatch
bool includes_data_;
// Should the callback also publishes the commit seq number
bool publish_seq_;
};
// For two_write_queues commit both the aborted batch and the cleanup batch and
// then published the seq
class WritePreparedRollbackPreReleaseCallback : public PreReleaseCallback {
public:
WritePreparedRollbackPreReleaseCallback(WritePreparedTxnDB* db,
DBImpl* db_impl,
SequenceNumber prep_seq,
SequenceNumber rollback_seq,
size_t prep_batch_cnt)
: db_(db),
db_impl_(db_impl),
prep_seq_(prep_seq),
rollback_seq_(rollback_seq),
prep_batch_cnt_(prep_batch_cnt) {
assert(prep_seq != kMaxSequenceNumber);
assert(rollback_seq != kMaxSequenceNumber);
assert(prep_batch_cnt_ > 0);
}
virtual Status Callback(SequenceNumber commit_seq,
bool is_mem_disabled) override {
assert(is_mem_disabled); // implies the 2nd queue
#ifdef NDEBUG
(void)is_mem_disabled;
#endif
const uint64_t last_commit_seq = commit_seq;
db_->AddCommitted(rollback_seq_, last_commit_seq);
for (size_t i = 0; i < prep_batch_cnt_; i++) {
db_->AddCommitted(prep_seq_ + i, last_commit_seq);
}
db_impl_->SetLastPublishedSequence(last_commit_seq);
return Status::OK();
}
private:
WritePreparedTxnDB* db_;
DBImpl* db_impl_;
SequenceNumber prep_seq_;
SequenceNumber rollback_seq_;
size_t prep_batch_cnt_;
};
// Count the number of sub-batches inside a batch. A sub-batch does not have
// duplicate keys.
struct SubBatchCounter : public WriteBatch::Handler {
explicit SubBatchCounter(std::map<uint32_t, const Comparator*>& comparators)
: comparators_(comparators), batches_(1) {}
std::map<uint32_t, const Comparator*>& comparators_;
using CFKeys = std::set<Slice, SetComparator>;
std::map<uint32_t, CFKeys> keys_;
size_t batches_;
size_t BatchCount() { return batches_; }
void AddKey(const uint32_t cf, const Slice& key);
void InitWithComp(const uint32_t cf);
Status MarkNoop(bool) override { return Status::OK(); }
Status MarkEndPrepare(const Slice&) override { return Status::OK(); }
Status MarkCommit(const Slice&) override { return Status::OK(); }
Status PutCF(uint32_t cf, const Slice& key, const Slice&) override {
AddKey(cf, key);
return Status::OK();
}
Status DeleteCF(uint32_t cf, const Slice& key) override {
AddKey(cf, key);
return Status::OK();
}
Status SingleDeleteCF(uint32_t cf, const Slice& key) override {
AddKey(cf, key);
return Status::OK();
}
Status MergeCF(uint32_t cf, const Slice& key, const Slice&) override {
AddKey(cf, key);
return Status::OK();
}
Status MarkBeginPrepare(bool) override { return Status::OK(); }
Status MarkRollback(const Slice&) override { return Status::OK(); }
bool WriteAfterCommit() const override { return false; }
};
} // namespace rocksdb
#endif // ROCKSDB_LITE
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