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Avoid unnecessary reads of uncompression dictionary in MultiGet (#6906) 

Summary:
We may sometimes read the uncompression dictionary when its not
necessary, when we lookup a key in an SST file but the index indicates
the key is not present. This can happen with index_type 3.
Pull Request resolved: https://github.com/facebook/rocksdb/pull/6906

Test Plan: make check

Reviewed By: cheng-chang

Differential Revision: D21828944

Pulled By: anand1976

fbshipit-source-id: 7aef4f0a39548d0874eafefd2687006d2652f9bb
This commit is contained in:
anand76 2020-06-01 19:41:58 -07:00 committed by Facebook GitHub Bot
parent 02f59ed669
commit 66942e8158
1 changed files with 18 additions and 12 deletions
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30
table/block_based/block_based_table_reader.cc
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@ -2441,18 +2441,7 @@ void BlockBasedTable::MultiGet(const ReadOptions& read_options,
CachableEntry<UncompressionDict> uncompression_dict;
Status uncompression_dict_status;
if (rep_->uncompression_dict_reader) {
uncompression_dict_status =
rep_->uncompression_dict_reader->GetOrReadUncompressionDictionary(
nullptr /* prefetch_buffer */, no_io,
sst_file_range.begin()->get_context, &lookup_context,
&uncompression_dict);
}
const UncompressionDict& dict = uncompression_dict.GetValue()
? *uncompression_dict.GetValue()
: UncompressionDict::GetEmptyDict();
bool uncompression_dict_inited = false;
size_t total_len = 0;
ReadOptions ro = read_options;
ro.read_tier = kBlockCacheTier;
@ -2481,6 +2470,15 @@ void BlockBasedTable::MultiGet(const ReadOptions& read_options,
continue;
}
if (!uncompression_dict_inited && rep_->uncompression_dict_reader) {
uncompression_dict_status =
rep_->uncompression_dict_reader->GetOrReadUncompressionDictionary(
nullptr /* prefetch_buffer */, no_io,
sst_file_range.begin()->get_context, &lookup_context,
&uncompression_dict);
uncompression_dict_inited = true;
}
if (!uncompression_dict_status.ok()) {
assert(!uncompression_dict_status.IsNotFound());
*(miter->s) = uncompression_dict_status;
@ -2504,6 +2502,9 @@ void BlockBasedTable::MultiGet(const ReadOptions& read_options,
BlockHandle handle = v.handle;
BlockCacheLookupContext lookup_data_block_context(
TableReaderCaller::kUserMultiGet);
const UncompressionDict& dict = uncompression_dict.GetValue()
? *uncompression_dict.GetValue()
: UncompressionDict::GetEmptyDict();
Status s = RetrieveBlock(
nullptr, ro, handle, dict, &(results.back()), BlockType::kData,
miter->get_context, &lookup_data_block_context,
@ -2523,6 +2524,11 @@ void BlockBasedTable::MultiGet(const ReadOptions& read_options,
if (total_len) {
char* scratch = nullptr;
const UncompressionDict& dict = uncompression_dict.GetValue()
? *uncompression_dict.GetValue()
: UncompressionDict::GetEmptyDict();
assert(uncompression_dict_inited || !rep_->uncompression_dict_reader);
assert(uncompression_dict_status.ok());
// If using direct IO, then scratch is not used, so keep it nullptr.
// If the blocks need to be uncompressed and we don't need the
// compressed blocks, then we can use a contiguous block of