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Add a unit test to assert number of preads (#4657)

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Summary:
We used to have a bug, which caused every block to be read twice, and none of our tests caught it. Add a very simply unit test to make sure that when reading a data block, we only issue one pread against the SST file.
Pull Request resolved: https://github.com/facebook/rocksdb/pull/4657

Differential Revision: D13005260

Pulled By: siying

fbshipit-source-id: 03167b554ad2451192b1707415536d7d05e9026c
This commit is contained in:
Siying Dong 2018-11-13 12:47:52 -08:00 committed by Facebook Github Bot
parent 05dab3aacd
commit abb1a8fc23
1 changed files with 55 additions and 0 deletions
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55
db/db_test2.cc
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@ -2515,6 +2515,61 @@ TEST_F(DBTest2, LiveFilesOmitObsoleteFiles) {
rocksdb::SyncPoint::GetInstance()->DisableProcessing();
}
TEST_F(DBTest2, TestNumPread) {
Options options = CurrentOptions();
// disable block cache
BlockBasedTableOptions table_options;
table_options.no_block_cache = true;
options.table_factory.reset(NewBlockBasedTableFactory(table_options));
Reopen(options);
env_->count_random_reads_ = true;
env_->random_file_open_counter_.store(0);
ASSERT_OK(Put("bar", "foo"));
ASSERT_OK(Put("foo", "bar"));
ASSERT_OK(Flush());
// After flush, we'll open the file and read footer, meta block,
// property block and index block.
ASSERT_EQ(4, env_->random_read_counter_.Read());
ASSERT_EQ(1, env_->random_file_open_counter_.load());
// One pread per a normal data block read
env_->random_file_open_counter_.store(0);
env_->random_read_counter_.Reset();
ASSERT_EQ("bar", Get("foo"));
ASSERT_EQ(1, env_->random_read_counter_.Read());
// All files are already opened.
ASSERT_EQ(0, env_->random_file_open_counter_.load());
env_->random_file_open_counter_.store(0);
env_->random_read_counter_.Reset();
ASSERT_OK(Put("bar2", "foo2"));
ASSERT_OK(Put("foo2", "bar2"));
ASSERT_OK(Flush());
// After flush, we'll open the file and read footer, meta block,
// property block and index block.
ASSERT_EQ(4, env_->random_read_counter_.Read());
ASSERT_EQ(1, env_->random_file_open_counter_.load());
// Compaction needs two input blocks, which requires 2 preads, and
// generate a new SST file which needs 4 preads (footer, meta block,
// property block and index block). In total 6.
env_->random_file_open_counter_.store(0);
env_->random_read_counter_.Reset();
ASSERT_OK(db_->CompactRange(CompactRangeOptions(), nullptr, nullptr));
ASSERT_EQ(6, env_->random_read_counter_.Read());
// All compactin input files should have already been opened.
ASSERT_EQ(1, env_->random_file_open_counter_.load());
// One pread per a normal data block read
env_->random_file_open_counter_.store(0);
env_->random_read_counter_.Reset();
ASSERT_EQ("foo2", Get("bar2"));
ASSERT_EQ(1, env_->random_read_counter_.Read());
// SST files are already opened.
ASSERT_EQ(0, env_->random_file_open_counter_.load());
}
TEST_F(DBTest2, TraceAndReplay) {
Options options = CurrentOptions();
options.merge_operator = MergeOperators::CreatePutOperator();