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table: Avoid useless allocations when updating cache on memtable flush completion

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we're unconditionally using make_combined_mutation_source(), which causes extra
allocations, even if memtable was flushed into a single sstable, which is the
most common case. memtable will only be flushed into more than one sstable if
TWCS is used and memtable had old data written into it due to out-of-order
writes.

Signed-off-by: Raphael S. Carvalho <raphaelsc@scylladb.com>
Message-Id: <20210205182028.439948-1-raphaelsc@scylladb.com>
This commit is contained in:
Raphael S. Carvalho
2021-02-05 15:20:28 -03:00
committed by Avi Kivity
parent 7910e745bc
commit e1261d10f1
1 changed files with 11 additions and 6 deletions
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17
table.cc
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@@ -389,13 +389,18 @@ table::add_sstable_and_update_cache(sstables::shared_sstable sst) {
future<>
table::update_cache(lw_shared_ptr<memtable> m, std::vector<sstables::shared_sstable> ssts) {
std::vector<mutation_source> sources;
sources.reserve(ssts.size());
for (auto& sst : ssts) {
sources.push_back(sst->as_mutation_source());
mutation_source_opt ms_opt;
if (ssts.size() == 1) {
ms_opt = ssts.front()->as_mutation_source();
} else {
std::vector<mutation_source> sources;
sources.reserve(ssts.size());
for (auto& sst : ssts) {
sources.push_back(sst->as_mutation_source());
}
ms_opt = make_combined_mutation_source(std::move(sources));
}
auto new_ssts_ms = make_combined_mutation_source(std::move(sources));
auto adder = row_cache::external_updater([this, m, ssts = std::move(ssts), new_ssts_ms = std::move(new_ssts_ms)] () mutable {
auto adder = row_cache::external_updater([this, m, ssts = std::move(ssts), new_ssts_ms = std::move(*ms_opt)] () mutable {
for (auto& sst : ssts) {
add_sstable(sst);
}