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use c++17's try_emplace if available (#5696)

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Summary:
This avoids rehashing the key in TrackKey() in case the key is not already
in the map of tracked keys, which will happen at least once per key used in a
transaction.

Additionally fix two typos.
Pull Request resolved: https://github.com/facebook/rocksdb/pull/5696

Differential Revision: D17210178

Pulled By: lth

fbshipit-source-id: 7e2c28e9e505c1d1c1535d435250cf2b191a6fdf
This commit is contained in:
jsteemann 2019-09-05 13:57:59 -07:00 committed by Facebook Github Bot
parent 20dec1401f
commit 19e8c9b64f
2 changed files with 16 additions and 4 deletions
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16
utilities/transactions/transaction_base.cc
View File

@ -633,18 +633,30 @@ void TransactionBaseImpl::TrackKey(TransactionKeyMap* key_map, uint32_t cfh_id,
const std::string& key, SequenceNumber seq,
bool read_only, bool exclusive) {
auto& cf_key_map = (*key_map)[cfh_id];
#ifdef __cpp_lib_unordered_map_try_emplace
// use c++17's try_emplace if available, to avoid rehashing the key
// in case it is not already in the map
auto result = cf_key_map.try_emplace(key, seq);
auto iter = result.first;
if (!result.second &&
seq < iter->second.seq) {
// Now tracking this key with an earlier sequence number
iter->second.seq = seq;
}
#else
auto iter = cf_key_map.find(key);
if (iter == cf_key_map.end()) {
auto result = cf_key_map.emplace(key, TransactionKeyMapInfo(seq));
auto result = cf_key_map.emplace(key, seq);
iter = result.first;
} else if (seq < iter->second.seq) {
// Now tracking this key with an earlier sequence number
iter->second.seq = seq;
}
#endif
// else we do not update the seq. The smaller the tracked seq, the stronger it
// the guarantee since it implies from the seq onward there has not been a
// concurrent update to the key. So we update the seq if it implies stronger
// guarantees, i.e., if it is smaller than the existing trakced seq.
// guarantees, i.e., if it is smaller than the existing tracked seq.
if (read_only) {
iter->second.num_reads++;

4
utilities/transactions/transaction_util.cc
View File

@ -75,8 +75,8 @@ Status TransactionUtil::CheckKey(DBImpl* db_impl, SuperVersion* sv,
if (cache_only) {
result = Status::TryAgain(
"Transaction ould not check for conflicts as the MemTable does not "
"countain a long enough history to check write at SequenceNumber: ",
"Transaction could not check for conflicts as the MemTable does not "
"contain a long enough history to check write at SequenceNumber: ",
ToString(snap_seq));
}
} else if (snap_seq < earliest_seq || min_uncommitted <= earliest_seq) {