Summary: Here are the major changes to the Merge Interface. It has been expanded to handle cases where the MergeOperator is not associative. It does so by stacking up merge operations while scanning through the key history (i.e.: during Get() or Compaction), until a valid Put/Delete/end-of-history is encountered; it then applies all of the merge operations in the correct sequence starting with the base/sentinel value. I have also introduced an "AssociativeMerge" function which allows the user to take advantage of associative merge operations (such as in the case of counters). The implementation will always attempt to merge the operations/operands themselves together when they are encountered, and will resort to the "stacking" method if and only if the "associative-merge" fails. This implementation is conjectured to allow MergeOperator to handle the general case, while still providing the user with the ability to take advantage of certain efficiencies in their own merge-operator / data-structure. NOTE: This is a preliminary diff. This must still go through a lot of review, revision, and testing. Feedback welcome! Test Plan: -This is a preliminary diff. I have only just begun testing/debugging it. -I will be testing this with the existing MergeOperator use-cases and unit-tests (counters, string-append, and redis-lists) -I will be "desk-checking" and walking through the code with the help gdb. -I will find a way of stress-testing the new interface / implementation using db_bench, db_test, merge_test, and/or db_stress. -I will ensure that my tests cover all cases: Get-Memtable, Get-Immutable-Memtable, Get-from-Disk, Iterator-Range-Scan, Flush-Memtable-to-L0, Compaction-L0-L1, Compaction-Ln-L(n+1), Put/Delete found, Put/Delete not-found, end-of-history, end-of-file, etc. -A lot of feedback from the reviewers. Reviewers: haobo, dhruba, zshao, emayanke Reviewed By: haobo CC: leveldb Differential Revision: https://reviews.facebook.net/D11499
217 lines
6.4 KiB
C++
217 lines
6.4 KiB
C++
// Copyright (c) 2012 Facebook.
|
|
|
|
|
|
#include "db/memtablelist.h"
|
|
|
|
#include <string>
|
|
#include "leveldb/db.h"
|
|
#include "db/memtable.h"
|
|
#include "leveldb/env.h"
|
|
#include "leveldb/iterator.h"
|
|
#include "util/coding.h"
|
|
|
|
namespace leveldb {
|
|
|
|
class InternalKeyComparator;
|
|
class Mutex;
|
|
class MemTableListIterator;
|
|
class VersionSet;
|
|
|
|
using std::list;
|
|
|
|
// Increase reference count on all underling memtables
|
|
void MemTableList::RefAll() {
|
|
for (list<MemTable*>::iterator it = memlist_.begin();
|
|
it != memlist_.end() ; ++it) {
|
|
(*it)->Ref();
|
|
}
|
|
}
|
|
|
|
// Drop reference count on all underling memtables
|
|
void MemTableList::UnrefAll() {
|
|
for (list<MemTable*>::iterator it = memlist_.begin();
|
|
it != memlist_.end() ; ++it) {
|
|
(*it)->Unref();
|
|
}
|
|
}
|
|
|
|
// Returns the total number of memtables in the list
|
|
int MemTableList::size() {
|
|
assert(num_flush_not_started_ <= size_);
|
|
return size_;
|
|
}
|
|
|
|
// Returns true if there is at least one memtable on which flush has
|
|
// not yet started.
|
|
bool MemTableList::IsFlushPending(int min_write_buffer_number_to_merge) {
|
|
if (num_flush_not_started_ >= min_write_buffer_number_to_merge) {
|
|
assert(imm_flush_needed.NoBarrier_Load() != nullptr);
|
|
return true;
|
|
}
|
|
return false;
|
|
}
|
|
|
|
// Returns the memtables that need to be flushed.
|
|
void MemTableList::PickMemtablesToFlush(std::vector<MemTable*>* ret) {
|
|
for (list<MemTable*>::reverse_iterator it = memlist_.rbegin();
|
|
it != memlist_.rend(); it++) {
|
|
MemTable* m = *it;
|
|
if (!m->flush_in_progress_) {
|
|
assert(!m->flush_completed_);
|
|
num_flush_not_started_--;
|
|
if (num_flush_not_started_ == 0) {
|
|
imm_flush_needed.Release_Store(nullptr);
|
|
}
|
|
m->flush_in_progress_ = true; // flushing will start very soon
|
|
ret->push_back(m);
|
|
}
|
|
}
|
|
}
|
|
|
|
// Record a successful flush in the manifest file
|
|
Status MemTableList::InstallMemtableFlushResults(
|
|
const std::vector<MemTable*> &mems,
|
|
VersionSet* vset, Status flushStatus,
|
|
port::Mutex* mu, Logger* info_log,
|
|
uint64_t file_number,
|
|
std::set<uint64_t>& pending_outputs) {
|
|
mu->AssertHeld();
|
|
|
|
// If the flush was not successful, then just reset state.
|
|
// Maybe a suceeding attempt to flush will be successful.
|
|
if (!flushStatus.ok()) {
|
|
for (MemTable* m : mems) {
|
|
assert(m->flush_in_progress_);
|
|
assert(m->file_number_ == 0);
|
|
|
|
m->flush_in_progress_ = false;
|
|
m->flush_completed_ = false;
|
|
m->edit_.Clear();
|
|
num_flush_not_started_++;
|
|
imm_flush_needed.Release_Store((void *)1);
|
|
pending_outputs.erase(file_number);
|
|
}
|
|
return flushStatus;
|
|
}
|
|
|
|
// flush was sucessful
|
|
bool first = true;
|
|
for (MemTable* m : mems) {
|
|
|
|
// All the edits are associated with the first memtable of this batch.
|
|
assert(first || m->GetEdits()->NumEntries() == 0);
|
|
first = false;
|
|
|
|
m->flush_completed_ = true;
|
|
m->file_number_ = file_number;
|
|
}
|
|
|
|
// if some other thread is already commiting, then return
|
|
Status s;
|
|
if (commit_in_progress_) {
|
|
return s;
|
|
}
|
|
|
|
// Only a single thread can be executing this piece of code
|
|
commit_in_progress_ = true;
|
|
|
|
// scan all memtables from the earliest, and commit those
|
|
// (in that order) that have finished flushing. Memetables
|
|
// are always committed in the order that they were created.
|
|
while (!memlist_.empty() && s.ok()) {
|
|
MemTable* m = memlist_.back(); // get the last element
|
|
if (!m->flush_completed_) {
|
|
break;
|
|
}
|
|
first = true;
|
|
|
|
Log(info_log,
|
|
"Level-0 commit table #%llu: started",
|
|
(unsigned long long)m->file_number_);
|
|
|
|
// this can release and reacquire the mutex.
|
|
s = vset->LogAndApply(&m->edit_, mu);
|
|
|
|
// All the later memtables that have the same filenum
|
|
// are part of the same batch. They can be committed now.
|
|
do {
|
|
if (s.ok()) { // commit new state
|
|
Log(info_log, "Level-0 commit table #%llu: done %s",
|
|
(unsigned long long)m->file_number_,
|
|
first ? "": "bulk");
|
|
memlist_.remove(m);
|
|
assert(m->file_number_ > 0);
|
|
|
|
// pending_outputs can be cleared only after the newly created file
|
|
// has been written to a committed version so that other concurrently
|
|
// executing compaction threads do not mistakenly assume that this
|
|
// file is not live.
|
|
pending_outputs.erase(m->file_number_);
|
|
m->Unref();
|
|
size_--;
|
|
} else {
|
|
//commit failed. setup state so that we can flush again.
|
|
Log(info_log, "Level-0 commit table #%llu: failed",
|
|
(unsigned long long)m->file_number_);
|
|
m->flush_completed_ = false;
|
|
m->flush_in_progress_ = false;
|
|
m->edit_.Clear();
|
|
num_flush_not_started_++;
|
|
pending_outputs.erase(m->file_number_);
|
|
m->file_number_ = 0;
|
|
imm_flush_needed.Release_Store((void *)1);
|
|
s = Status::IOError("Unable to commit flushed memtable");
|
|
}
|
|
first = false;
|
|
} while (!memlist_.empty() && (m = memlist_.back()) &&
|
|
m->file_number_ == file_number);
|
|
}
|
|
commit_in_progress_ = false;
|
|
return s;
|
|
}
|
|
|
|
// New memtables are inserted at the front of the list.
|
|
void MemTableList::Add(MemTable* m) {
|
|
assert(size_ >= num_flush_not_started_);
|
|
size_++;
|
|
memlist_.push_front(m);
|
|
num_flush_not_started_++;
|
|
if (num_flush_not_started_ == 1) {
|
|
imm_flush_needed.Release_Store((void *)1);
|
|
}
|
|
}
|
|
|
|
// Returns an estimate of the number of bytes of data in use.
|
|
size_t MemTableList::ApproximateMemoryUsage() {
|
|
size_t size = 0;
|
|
for (list<MemTable*>::iterator it = memlist_.begin();
|
|
it != memlist_.end(); ++it) {
|
|
size += (*it)->ApproximateMemoryUsage();
|
|
}
|
|
return size;
|
|
}
|
|
|
|
// Search all the memtables starting from the most recent one.
|
|
// Return the most recent value found, if any.
|
|
// Operands stores the list of merge operations to apply, so far.
|
|
bool MemTableList::Get(const LookupKey& key, std::string* value, Status* s,
|
|
std::deque<std::string>* operands,
|
|
const Options& options) {
|
|
for (list<MemTable*>::iterator it = memlist_.begin();
|
|
it != memlist_.end(); ++it) {
|
|
if ((*it)->Get(key, value, s, operands, options)) {
|
|
return true;
|
|
}
|
|
}
|
|
return false;
|
|
}
|
|
|
|
void MemTableList::GetMemTables(std::vector<MemTable*>* output) {
|
|
for (list<MemTable*>::iterator it = memlist_.begin();
|
|
it != memlist_.end(); ++it) {
|
|
output->push_back(*it);
|
|
}
|
|
}
|
|
|
|
} // namespace leveldb
|