rocksdb/table/cleanable_test.cc
Peter Dillinger 9d0cae7104 Eliminate unnecessary (slow) block cache Ref()ing in MultiGet (#9899)
Summary:
When MultiGet() determines that multiple query keys can be
served by examining the same data block in block cache (one Lookup()),
each PinnableSlice referring to data in that data block needs to hold
on to the block in cache so that they can be released at arbitrary
times by the API user. Historically this is accomplished with extra
calls to Ref() on the Handle from Lookup(), with each PinnableSlice
cleanup calling Release() on the Handle, but this creates extra
contention on the block cache for the extra Ref()s and Release()es,
especially because they hit the same cache shard repeatedly.

In the case of merge operands (possibly more cases?), the problem was
compounded by doing an extra Ref()+eventual Release() for each merge
operand for a key reusing a block (which could be the same key!), rather
than one Ref() per key. (Note: the non-shared case with `biter` was
already one per key.)

This change optimizes MultiGet not to rely on these extra, contentious
Ref()+Release() calls by instead, in the shared block case, wrapping
the cache Release() cleanup in a refcounted object referenced by the
PinnableSlices, such that after the last wrapped reference is released,
the cache entry is Release()ed. Relaxed atomic refcounts should be
much faster than mutex-guarded Ref() and Release(), and much less prone
to a performance cliff when MultiGet() does a lot of block sharing.

Note that I did not use std::shared_ptr, because that would require an
extra indirection object (shared_ptr itself new/delete) in order to
associate a ref increment/decrement with a Cleanable cleanup entry. (If
I assumed it was the size of two pointers, I could do some hackery to
make it work without the extra indirection, but that's too fragile.)

Some details:
* Fixed (removed) extra block cache tracing entries in cases of cache
entry reuse in MultiGet, but it's likely that in some other cases traces
are missing (XXX comment inserted)
* Moved existing implementations for cleanable.h from iterator.cc to
new cleanable.cc
* Improved API comments on Cleanable
* Added a public SharedCleanablePtr class to cleanable.h in case others
could benefit from the same pattern (potentially many Cleanables and/or
smart pointers referencing a shared Cleanable)
* Add a typedef for MultiGetContext::Mask
* Some variable renaming for clarity

Pull Request resolved: https://github.com/facebook/rocksdb/pull/9899

Test Plan:
Added unit tests for SharedCleanablePtr.

Greatly enhanced ability of existing tests to detect cache use-after-free.
* Release PinnableSlices from MultiGet as they are read rather than in
bulk (in db_test_util wrapper).
* In ASAN build, default to using a trivially small LRUCache for block_cache
so that entries are immediately erased when unreferenced. (Updated two
tests that depend on caching.) New ASAN testsuite running time seems
OK to me.

If I introduce a bug into my implementation where we skip the shared
cleanups on block reuse, ASAN detects the bug in
`db_basic_test *MultiGet*`. If I remove either of the above testing
enhancements, the bug is not detected.

Consider for follow-up work: manipulate or randomize ordering of
PinnableSlice use and release from MultiGet db_test_util wrapper. But in
typical cases, natural ordering gives pretty good functional coverage.

Performance test:
In the extreme (but possible) case of MultiGetting the same or adjacent keys
in a batch, throughput can improve by an order of magnitude.
`./db_bench -benchmarks=multireadrandom -db=/dev/shm/testdb -readonly -num=5 -duration=10 -threads=20 -multiread_batched -batch_size=200`
Before ops/sec, num=5: 1,384,394
Before ops/sec, num=500: 6,423,720
After ops/sec, num=500: 10,658,794
After ops/sec, num=5: 16,027,257

Also note that previously, with high parallelism, having query keys
concentrated in a single block was worse than spreading them out a bit. Now
concentrated in a single block is faster than spread out, which is hopefully
consistent with natural expectation.

Random query performance: with num=1000000, over 999 x 10s runs running before & after simultaneously (each -threads=12):
Before: multireadrandom [AVG    999 runs] : 1088699 (± 7344) ops/sec;  120.4 (± 0.8 ) MB/sec
After: multireadrandom [AVG    999 runs] : 1090402 (± 7230) ops/sec;  120.6 (± 0.8 ) MB/sec
Possibly better, possibly in the noise.

Reviewed By: anand1976

Differential Revision: D35907003

Pulled By: pdillinger

fbshipit-source-id: bbd244d703649a8ca12d476f2d03853ed9d1a17e
2022-04-26 21:59:24 -07:00

391 lines
9.2 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 "rocksdb/cleanable.h"
#include <gtest/gtest.h>
#include <functional>
#include "port/port.h"
#include "port/stack_trace.h"
#include "rocksdb/iostats_context.h"
#include "rocksdb/perf_context.h"
#include "test_util/testharness.h"
#include "test_util/testutil.h"
namespace ROCKSDB_NAMESPACE {
class CleanableTest : public testing::Test {};
// Use this to keep track of the cleanups that were actually performed
void Multiplier(void* arg1, void* arg2) {
int* res = reinterpret_cast<int*>(arg1);
int* num = reinterpret_cast<int*>(arg2);
*res *= *num;
}
// the first Cleanup is on stack and the rest on heap, so test with both cases
TEST_F(CleanableTest, Register) {
int n2 = 2, n3 = 3;
int res = 1;
{ Cleanable c1; }
// ~Cleanable
ASSERT_EQ(1, res);
res = 1;
{
Cleanable c1;
c1.RegisterCleanup(Multiplier, &res, &n2); // res = 2;
}
// ~Cleanable
ASSERT_EQ(2, res);
res = 1;
{
Cleanable c1;
c1.RegisterCleanup(Multiplier, &res, &n2); // res = 2;
c1.RegisterCleanup(Multiplier, &res, &n3); // res = 2 * 3;
}
// ~Cleanable
ASSERT_EQ(6, res);
// Test the Reset does cleanup
res = 1;
{
Cleanable c1;
c1.RegisterCleanup(Multiplier, &res, &n2); // res = 2;
c1.RegisterCleanup(Multiplier, &res, &n3); // res = 2 * 3;
c1.Reset();
ASSERT_EQ(6, res);
}
// ~Cleanable
ASSERT_EQ(6, res);
// Test Clenable is usable after Reset
res = 1;
{
Cleanable c1;
c1.RegisterCleanup(Multiplier, &res, &n2); // res = 2;
c1.Reset();
ASSERT_EQ(2, res);
c1.RegisterCleanup(Multiplier, &res, &n3); // res = 2 * 3;
}
// ~Cleanable
ASSERT_EQ(6, res);
}
// the first Cleanup is on stack and the rest on heap,
// so test all the combinations of them
TEST_F(CleanableTest, Delegation) {
int n2 = 2, n3 = 3, n5 = 5, n7 = 7;
int res = 1;
{
Cleanable c2;
{
Cleanable c1;
c1.RegisterCleanup(Multiplier, &res, &n2); // res = 2;
c1.DelegateCleanupsTo(&c2);
}
// ~Cleanable
ASSERT_EQ(1, res);
}
// ~Cleanable
ASSERT_EQ(2, res);
res = 1;
{
Cleanable c2;
{
Cleanable c1;
c1.DelegateCleanupsTo(&c2);
}
// ~Cleanable
ASSERT_EQ(1, res);
}
// ~Cleanable
ASSERT_EQ(1, res);
res = 1;
{
Cleanable c2;
{
Cleanable c1;
c1.RegisterCleanup(Multiplier, &res, &n2); // res = 2;
c1.RegisterCleanup(Multiplier, &res, &n3); // res = 2 * 3;
c1.DelegateCleanupsTo(&c2);
}
// ~Cleanable
ASSERT_EQ(1, res);
}
// ~Cleanable
ASSERT_EQ(6, res);
res = 1;
{
Cleanable c2;
c2.RegisterCleanup(Multiplier, &res, &n5); // res = 5;
{
Cleanable c1;
c1.RegisterCleanup(Multiplier, &res, &n2); // res = 2;
c1.RegisterCleanup(Multiplier, &res, &n3); // res = 2 * 3;
c1.DelegateCleanupsTo(&c2); // res = 2 * 3 * 5;
}
// ~Cleanable
ASSERT_EQ(1, res);
}
// ~Cleanable
ASSERT_EQ(30, res);
res = 1;
{
Cleanable c2;
c2.RegisterCleanup(Multiplier, &res, &n5); // res = 5;
c2.RegisterCleanup(Multiplier, &res, &n7); // res = 5 * 7;
{
Cleanable c1;
c1.RegisterCleanup(Multiplier, &res, &n2); // res = 2;
c1.RegisterCleanup(Multiplier, &res, &n3); // res = 2 * 3;
c1.DelegateCleanupsTo(&c2); // res = 2 * 3 * 5 * 7;
}
// ~Cleanable
ASSERT_EQ(1, res);
}
// ~Cleanable
ASSERT_EQ(210, res);
res = 1;
{
Cleanable c2;
c2.RegisterCleanup(Multiplier, &res, &n5); // res = 5;
c2.RegisterCleanup(Multiplier, &res, &n7); // res = 5 * 7;
{
Cleanable c1;
c1.RegisterCleanup(Multiplier, &res, &n2); // res = 2;
c1.DelegateCleanupsTo(&c2); // res = 2 * 5 * 7;
}
// ~Cleanable
ASSERT_EQ(1, res);
}
// ~Cleanable
ASSERT_EQ(70, res);
res = 1;
{
Cleanable c2;
c2.RegisterCleanup(Multiplier, &res, &n5); // res = 5;
c2.RegisterCleanup(Multiplier, &res, &n7); // res = 5 * 7;
{
Cleanable c1;
c1.DelegateCleanupsTo(&c2); // res = 5 * 7;
}
// ~Cleanable
ASSERT_EQ(1, res);
}
// ~Cleanable
ASSERT_EQ(35, res);
res = 1;
{
Cleanable c2;
c2.RegisterCleanup(Multiplier, &res, &n5); // res = 5;
{
Cleanable c1;
c1.DelegateCleanupsTo(&c2); // res = 5;
}
// ~Cleanable
ASSERT_EQ(1, res);
}
// ~Cleanable
ASSERT_EQ(5, res);
}
static void ReleaseStringHeap(void* s, void*) {
delete reinterpret_cast<const std::string*>(s);
}
class PinnableSlice4Test : public PinnableSlice {
public:
void TestStringIsRegistered(std::string* s) {
ASSERT_TRUE(cleanup_.function == ReleaseStringHeap);
ASSERT_EQ(cleanup_.arg1, s);
ASSERT_EQ(cleanup_.arg2, nullptr);
ASSERT_EQ(cleanup_.next, nullptr);
}
};
// Putting the PinnableSlice tests here due to similarity to Cleanable tests
TEST_F(CleanableTest, PinnableSlice) {
int n2 = 2;
int res = 1;
const std::string const_str = "123";
{
res = 1;
PinnableSlice4Test value;
Slice slice(const_str);
value.PinSlice(slice, Multiplier, &res, &n2);
std::string str;
str.assign(value.data(), value.size());
ASSERT_EQ(const_str, str);
}
// ~Cleanable
ASSERT_EQ(2, res);
{
res = 1;
PinnableSlice4Test value;
Slice slice(const_str);
{
Cleanable c1;
c1.RegisterCleanup(Multiplier, &res, &n2); // res = 2;
value.PinSlice(slice, &c1);
}
// ~Cleanable
ASSERT_EQ(1, res); // cleanups must have be delegated to value
std::string str;
str.assign(value.data(), value.size());
ASSERT_EQ(const_str, str);
}
// ~Cleanable
ASSERT_EQ(2, res);
{
PinnableSlice4Test value;
Slice slice(const_str);
value.PinSelf(slice);
std::string str;
str.assign(value.data(), value.size());
ASSERT_EQ(const_str, str);
}
{
PinnableSlice4Test value;
std::string* self_str_ptr = value.GetSelf();
self_str_ptr->assign(const_str);
value.PinSelf();
std::string str;
str.assign(value.data(), value.size());
ASSERT_EQ(const_str, str);
}
}
static void Decrement(void* intptr, void*) { --*static_cast<int*>(intptr); }
// Allow unit testing moved-from data
template <class T>
void MarkInitializedForClangAnalyze(T& t) {
// No net effect, but confuse analyzer. (Published advice doesn't work.)
char* p = reinterpret_cast<char*>(&t);
std::swap(*p, *p);
}
TEST_F(CleanableTest, SharedWrapCleanables) {
int val = 5;
Cleanable c1, c2;
c1.RegisterCleanup(&Decrement, &val, nullptr);
c1.RegisterCleanup(&Decrement, &val, nullptr);
ASSERT_TRUE(c1.HasCleanups());
ASSERT_FALSE(c2.HasCleanups());
SharedCleanablePtr scp1;
ASSERT_EQ(scp1.get(), nullptr);
// No-ops
scp1.RegisterCopyWith(&c2);
scp1.MoveAsCleanupTo(&c2);
ASSERT_FALSE(c2.HasCleanups());
c2.RegisterCleanup(&Decrement, &val, nullptr);
c2.RegisterCleanup(&Decrement, &val, nullptr);
c2.RegisterCleanup(&Decrement, &val, nullptr);
scp1.Allocate();
ASSERT_NE(scp1.get(), nullptr);
ASSERT_FALSE(scp1->HasCleanups());
// Copy ctor (alias scp2 = scp1)
SharedCleanablePtr scp2{scp1};
ASSERT_EQ(scp1.get(), scp2.get());
c1.DelegateCleanupsTo(&*scp1);
ASSERT_TRUE(scp1->HasCleanups());
ASSERT_TRUE(scp2->HasCleanups());
ASSERT_FALSE(c1.HasCleanups());
SharedCleanablePtr scp3;
ASSERT_EQ(scp3.get(), nullptr);
// Copy operator (alias scp3 = scp2 = scp1)
scp3 = scp2;
// Make scp2 point elsewhere
scp2.Allocate();
c2.DelegateCleanupsTo(&*scp2);
ASSERT_EQ(val, 5);
// Move operator, invoke old c2 cleanups
scp2 = std::move(scp1);
ASSERT_EQ(val, 2);
MarkInitializedForClangAnalyze(scp1);
ASSERT_EQ(scp1.get(), nullptr);
// Move ctor
{
SharedCleanablePtr scp4{std::move(scp3)};
MarkInitializedForClangAnalyze(scp3);
ASSERT_EQ(scp3.get(), nullptr);
ASSERT_EQ(scp4.get(), scp2.get());
scp2.Reset();
ASSERT_EQ(val, 2);
// invoke old c1 cleanups
}
ASSERT_EQ(val, 0);
}
TEST_F(CleanableTest, CleanableWrapShared) {
int val = 5;
SharedCleanablePtr scp1, scp2;
scp1.Allocate();
scp1->RegisterCleanup(&Decrement, &val, nullptr);
scp1->RegisterCleanup(&Decrement, &val, nullptr);
scp2.Allocate();
scp2->RegisterCleanup(&Decrement, &val, nullptr);
scp2->RegisterCleanup(&Decrement, &val, nullptr);
scp2->RegisterCleanup(&Decrement, &val, nullptr);
{
Cleanable c1;
{
Cleanable c2, c3;
scp1.RegisterCopyWith(&c1);
scp1.MoveAsCleanupTo(&c2);
ASSERT_TRUE(c1.HasCleanups());
ASSERT_TRUE(c2.HasCleanups());
ASSERT_EQ(scp1.get(), nullptr);
scp2.MoveAsCleanupTo(&c3);
ASSERT_TRUE(c3.HasCleanups());
ASSERT_EQ(scp2.get(), nullptr);
c2.Reset();
ASSERT_FALSE(c2.HasCleanups());
ASSERT_EQ(val, 5);
// invoke cleanups from scp2
}
ASSERT_EQ(val, 2);
// invoke cleanups from scp1
}
ASSERT_EQ(val, 0);
}
} // namespace ROCKSDB_NAMESPACE
int main(int argc, char** argv) {
ROCKSDB_NAMESPACE::port::InstallStackTraceHandler();
::testing::InitGoogleTest(&argc, argv);
return RUN_ALL_TESTS();
}