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opt(server): Short-circuit ExecuteAsync(). (#1601)

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* feat(server): Short-circuit ExecuteAsync().

* Do not leak (hopefully :)

* Add documentation about coordinator_index_

* Use ServerState::tlocal()->thread_index()
This commit is contained in:
Shahar Mike 2023-07-31 12:12:59 +03:00 • committed by GitHub
parent 4c85d5825d
commit fba0800081
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2 changed files with 15 additions and 6 deletions
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17
src/server/transaction.cc
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@ -136,7 +136,7 @@ void Transaction::InitShardData(absl::Span<const PerShardCache> shard_index, siz
sd.arg_count = si.args.size();
sd.arg_start = args_.size();
// Multi transactions can re-intitialize on different shards, so clear ACTIVE flag.
// Multi transactions can re-initialize on different shards, so clear ACTIVE flag.
if (multi_)
sd.local_mask &= ~ACTIVE;
@ -212,7 +212,7 @@ void Transaction::StoreKeysInArgs(KeyIndex key_index, bool rev_mapping) {
/**
*
* There are 4 options that we consider here:
* a. T spans a single shard and its not multi.
* a. T spans a single shard and it's not multi.
* unique_shard_id_ is predefined before the schedule() is called.
* In that case only a single thread will be scheduled and it will use shard_data[0] just because
* shard_data.size() = 1. Coordinator thread can access any data because there is a
@ -828,7 +828,7 @@ void Transaction::ExecuteAsync() {
// We do not necessarily Execute this transaction in 'cb' below. It well may be that it will be
// executed by the engine shard once it has been armed and coordinator thread will finish the
// transaction before engine shard thread stops accessing it. Therefore, we increase reference
// by number of callbacks accessesing 'this' to allow callbacks to execute shard->Execute(this);
// by number of callbacks accessing 'this' to allow callbacks to execute shard->Execute(this);
// safely.
use_count_.fetch_add(unique_shard_cnt_, memory_order_relaxed);
@ -844,6 +844,15 @@ void Transaction::ExecuteAsync() {
// IsArmedInShard in other threads.
run_count_.store(unique_shard_cnt_, memory_order_release);
// Execute inline when we can. We can't use coordinator_index_ because we may offload this
// function to run in a different thread.
if (unique_shard_cnt_ == 1 && ServerState::tlocal()->thread_index() == unique_shard_id_) {
DVLOG(1) << "Short-circuit ExecuteAsync " << DebugId();
EngineShard::tlocal()->PollExecution("exec_cb", this);
intrusive_ptr_release(this); // against use_count_.fetch_add above.
return;
}
// We verify seq lock has the same generation number. See below for more info.
auto cb = [seq, this] {
EngineShard* shard = EngineShard::tlocal();
@ -856,7 +865,7 @@ void Transaction::ExecuteAsync() {
DVLOG(3) << "PollExecCb " << DebugId() << " sid(" << shard->shard_id() << ") "
<< run_count_.load(memory_order_relaxed);
// We also make sure that for mult-operation transactions like Multi/Eval
// We also make sure that for multi-operation transactions like Multi/Eval
// this callback runs on a correct operation. We want to avoid a situation
// where the first operation is executed and the second operation is armed and
// now this callback from the previous operation finally runs and calls PollExecution.