write_thread.cc
// Copyright (c) 2013, Facebook, Inc. All rights reserved.
// This source code is licensed under the BSD-style license found in the
// LICENSE file in the root directory of this source tree. An additional grant
// of patent rights can be found in the PATENTS file in the same directory.
#include "db/write_thread.h"
namespace rocksdb {
Status WriteThread::EnterWriteThread(WriteThread::Writer* w,
uint64_t expiration_time) {
// the following code block pushes the current writer "w" into the writer
// queue "writers_" and wait until one of the following conditions met:
// 1. the job of "w" has been done by some other writers.
// 2. "w" becomes the first writer in "writers_"
// 3. "w" timed-out.
writers_.push_back(w);
bool timed_out = false;
while (!w->done && w != writers_.front()) {
if (expiration_time == 0) {
w->cv.Wait();
} else if (w->cv.TimedWait(expiration_time)) {
if (w->in_batch_group) {
// then it means the front writer is currently doing the
// write on behalf of this "timed-out" writer. Then it
// should wait until the write completes.
expiration_time = 0;
} else {
timed_out = true;
break;
}
}
}
if (timed_out) {
#ifndef NDEBUG
bool found = false;
#endif
for (auto iter = writers_.begin(); iter != writers_.end(); iter++) {
if (*iter == w) {
writers_.erase(iter);
#ifndef NDEBUG
found = true;
#endif
break;
}
}
#ifndef NDEBUG
assert(found);
#endif
// writers_.front() might still be in cond_wait without a time-out.
// As a result, we need to signal it to wake it up. Otherwise no
// one else will wake him up, and RocksDB will hang.
if (!writers_.empty()) {
writers_.front()->cv.Signal();
}
return Status::TimedOut();
}
return Status::OK();
}
void WriteThread::ExitWriteThread(WriteThread::Writer* w,
WriteThread::Writer* last_writer,
Status status) {
// Pop out the current writer and all writers being pushed before the
// current writer from the writer queue.
while (!writers_.empty()) {
Writer* ready = writers_.front();
writers_.pop_front();
if (ready != w) {
ready->status = status;
ready->done = true;
ready->cv.Signal();
}
if (ready == last_writer) break;
}
// Notify new head of write queue
if (!writers_.empty()) {
writers_.front()->cv.Signal();
}
}
// This function will be called only when the first writer succeeds.
// All writers in the to-be-built batch group will be processed.
//
// REQUIRES: Writer list must be non-empty
// REQUIRES: First writer must have a non-nullptr batch
void WriteThread::BuildBatchGroup(WriteThread::Writer** last_writer,
autovector<WriteBatch*>* write_batch_group) {
assert(!writers_.empty());
Writer* first = writers_.front();
assert(first->batch != nullptr);
size_t size = WriteBatchInternal::ByteSize(first->batch);
write_batch_group->push_back(first->batch);
// Allow the group to grow up to a maximum size, but if the
// original write is small, limit the growth so we do not slow
// down the small write too much.
size_t max_size = 1 << 20;
if (size <= (128<<10)) {
max_size = size + (128<<10);
}
*last_writer = first;
std::deque<Writer*>::iterator iter = writers_.begin();
++iter; // Advance past "first"
for (; iter != writers_.end(); ++iter) {
Writer* w = *iter;
if (w->sync && !first->sync) {
// Do not include a sync write into a batch handled by a non-sync write.
break;
}
if (!w->disableWAL && first->disableWAL) {
// Do not include a write that needs WAL into a batch that has
// WAL disabled.
break;
}
if (w->timeout_hint_us < first->timeout_hint_us) {
// Do not include those writes with shorter timeout. Otherwise, we might
// execute a write that should instead be aborted because of timeout.
break;
}
if (w->batch == nullptr) {
// Do not include those writes with nullptr batch. Those are not writes,
// those are something else. They want to be alone
break;
}
size += WriteBatchInternal::ByteSize(w->batch);
if (size > max_size) {
// Do not make batch too big
break;
}
write_batch_group->push_back(w->batch);
w->in_batch_group = true;
*last_writer = w;
}
}
} // namespace rocksdb