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sstables: avoid calls to resize for vectors

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resize is considered harmful, since it will attempt to allocate memory
and initialize each element of the vector. This can cause reactor stalls
that correlates to latency peaks.

A better idiom is reserve first - so we know we will have enough memory
and won't have to move contents - and push_back/emplace_back each
individual member.

Signed-off-by: Glauber Costa <glauber@scylladb.com>
This commit is contained in:
Glauber Costa
2018-03-14 13:32:36 -04:00
parent 0d9488eae6
commit a33f0d6f92
1 changed files with 25 additions and 14 deletions
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39
sstables/sstables.cc
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@@ -428,7 +428,9 @@ parse(random_access_reader& in, Size& len, utils::chunked_vector<Members>& arr)
auto eoarr = [count, len] { return *count == len; };
return do_until(eoarr, [count, &in, &arr] {
return parse(in, arr[(*count)++]);
arr.emplace_back();
(*count)++;
return parse(in, arr.back());
});
}
@@ -443,7 +445,7 @@ parse(random_access_reader& in, Size& len, utils::chunked_vector<Members>& arr)
auto *nr = reinterpret_cast<const net::packed<Members> *>(buf.get());
for (size_t i = 0; i < now; ++i) {
arr[*done + i] = net::ntoh(nr[i]);
arr.push_back(net::ntoh(nr[i]));
}
*done += now;
return make_ready_future<stop_iteration>(*done == len ? stop_iteration::yes : stop_iteration::no);
@@ -458,7 +460,7 @@ future<> parse(random_access_reader& in, disk_array<Size, Members>& arr) {
auto len = make_lw_shared<Size>();
auto f = parse(in, *len);
return f.then([&in, &arr, len] {
arr.elements.resize(*len);
arr.elements.reserve(*len);
return parse(in, *len, arr.elements);
}).finally([len] {});
}
@@ -789,20 +791,25 @@ future<> parse(random_access_reader& in, utils::estimated_histogram& eh) {
if (length == 0) {
throw malformed_sstable_exception("Estimated histogram with zero size found. Can't continue!");
}
eh.bucket_offsets.resize(length - 1);
eh.buckets.resize(length);
eh.bucket_offsets.reserve(length - 1);
eh.buckets.reserve(length);
auto type_size = sizeof(uint64_t) * 2;
return in.read_exactly(length * type_size).then([&eh, length, type_size] (auto buf) {
check_buf_size(buf, length * type_size);
auto *nr = reinterpret_cast<const net::packed<uint64_t> *>(buf.get());
size_t j = 0;
for (size_t i = 0; i < length; ++i) {
eh.bucket_offsets[i == 0 ? 0 : i - 1] = net::ntoh(nr[j++]);
eh.buckets[i] = net::ntoh(nr[j++]);
}
return make_ready_future<>();
return do_with(size_t(0), [nr, &eh, length] (size_t& j) mutable {
return do_until([&eh, length] { return eh.buckets.size() == length; }, [nr, &eh, &j] () mutable {
auto offset = net::ntoh(nr[j++]);
auto bucket = net::ntoh(nr[j++]);
if (eh.buckets.size() > 0) {
eh.bucket_offsets.push_back(offset);
}
eh.buckets.push_back(bucket);
return make_ready_future<>();
});
});
});
});
}
@@ -817,13 +824,17 @@ inline void write(file_writer& out, const utils::estimated_histogram& eh) {
uint64_t buckets;
};
std::vector<element> elements;
elements.resize(eh.buckets.size());
elements.reserve(eh.buckets.size());
auto *offsets_nr = reinterpret_cast<const net::packed<uint64_t> *>(eh.bucket_offsets.data());
auto *buckets_nr = reinterpret_cast<const net::packed<uint64_t> *>(eh.buckets.data());
for (size_t i = 0; i < eh.buckets.size(); i++) {
elements[i].offsets = net::hton(offsets_nr[i == 0 ? 0 : i - 1]);
elements[i].buckets = net::hton(buckets_nr[i]);
auto offsets = net::hton(offsets_nr[i == 0 ? 0 : i - 1]);
auto buckets = net::hton(buckets_nr[i]);
elements.emplace_back(element{offsets, buckets});
if (need_preempt()) {
seastar::thread::yield();
}
}
auto p = reinterpret_cast<const char*>(elements.data());