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Reduce arena allocations when materializing RocksDB range read results #13273

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Reduce arena allocations when materializing RocksDB range read results #13273

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98bd30e
perf(fdbclient): reduce arena allocations in MutationRef deep-copy co…
pchintar May 23, 2026
3d0286d
perf(kvstore): Reduce arena allocations for range read results
pchintar May 24, 2026
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17 changes: 15 additions & 2 deletions fdbclient/include/fdbclient/FDBTypes.h
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Original file line number Diff line number Diff line change
Expand Up @@ -455,10 +455,23 @@ struct KeyValueRef {
KeyRef key;
ValueRef value;
KeyValueRef() {}

KeyValueRef(const KeyRef& key, const ValueRef& value) : key(key), value(value) {}
KeyValueRef(Arena& a, const KeyValueRef& copyFrom) : key(a, copyFrom.key), value(a, copyFrom.value) {}

KeyValueRef(Arena& a, const KeyRef& key, const ValueRef& value) {
StringRef storage = makeString(key.size() + value.size(), a);
uint8_t* dst = mutateString(storage);

key.copyTo(dst);
value.copyTo(dst + key.size());

this->key = KeyRef(storage.begin(), key.size());
this->value = ValueRef(storage.begin() + key.size(), value.size());
}

KeyValueRef(Arena& a, const KeyValueRef& copyFrom) : KeyValueRef(a, copyFrom.key, copyFrom.value) {}

bool operator==(const KeyValueRef& r) const { return key == r.key && value == r.value; }
bool operator!=(const KeyValueRef& r) const { return key != r.key || value != r.value; }
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@saintstack saintstack May 29, 2026

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Good


int expectedSize() const { return key.expectedSize() + value.expectedSize(); }

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16 changes: 10 additions & 6 deletions fdbserver/kvstore/KeyValueStoreRocksDB.actor.cpp
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Original file line number Diff line number Diff line change
Expand Up @@ -1916,9 +1916,11 @@ struct RocksDBKeyValueStore : IKeyValueStore {
auto cursor = readIter.iter;
cursor->Seek(toSlice(a.keys.begin));
while (cursor->Valid() && toStringRef(cursor->key()) < a.keys.end) {
KeyValueRef kv(toStringRef(cursor->key()), toStringRef(cursor->value()));
accumulatedBytes += sizeof(KeyValueRef) + kv.expectedSize();
result.push_back_deep(result.arena(), kv);
KeyRef key = toStringRef(cursor->key());
ValueRef value = toStringRef(cursor->value());

accumulatedBytes += sizeof(KeyValueRef) + key.expectedSize() + value.expectedSize();
result.emplace_back_deep(result.arena(), key, value);
// Calling `cursor->Next()` is potentially expensive, so short-circut here just in case.
if (result.size() >= a.rowLimit || accumulatedBytes >= a.byteLimit) {
break;
Expand Down Expand Up @@ -1949,9 +1951,11 @@ struct RocksDBKeyValueStore : IKeyValueStore {
cursor->Prev();
}
while (cursor->Valid() && toStringRef(cursor->key()) >= a.keys.begin) {
KeyValueRef kv(toStringRef(cursor->key()), toStringRef(cursor->value()));
accumulatedBytes += sizeof(KeyValueRef) + kv.expectedSize();
result.push_back_deep(result.arena(), kv);
KeyRef key = toStringRef(cursor->key());
ValueRef value = toStringRef(cursor->value());

accumulatedBytes += sizeof(KeyValueRef) + key.expectedSize() + value.expectedSize();
result.emplace_back_deep(result.arena(), key, value);
// Calling `cursor->Prev()` is potentially expensive, so short-circut here just in case.
if (result.size() >= -a.rowLimit || accumulatedBytes >= a.byteLimit) {
break;
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16 changes: 10 additions & 6 deletions fdbserver/kvstore/KeyValueStoreShardedRocksDB.actor.cpp
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Original file line number Diff line number Diff line change
Expand Up @@ -1111,9 +1111,11 @@ int readRangeInDb(PhysicalShard* shard,
auto* cursor = readIter->iter.get();
cursor->Seek(toSlice(range.begin));
while (cursor->Valid() && toStringRef(cursor->key()) < range.end) {
KeyValueRef kv(toStringRef(cursor->key()), toStringRef(cursor->value()));
accumulatedBytes += sizeof(KeyValueRef) + kv.expectedSize();
result->push_back_deep(result->arena(), kv);
KeyRef key = toStringRef(cursor->key());
ValueRef value = toStringRef(cursor->value());

accumulatedBytes += sizeof(KeyValueRef) + key.expectedSize() + value.expectedSize();
result->emplace_back_deep(result->arena(), key, value);
// Calling `cursor->Next()` is potentially expensive, so short-circut here just in case.
if (result->size() >= rowLimit || accumulatedBytes >= byteLimit) {
break;
Expand All @@ -1128,9 +1130,11 @@ int readRangeInDb(PhysicalShard* shard,
cursor->Prev();
}
while (cursor->Valid() && toStringRef(cursor->key()) >= range.begin) {
KeyValueRef kv(toStringRef(cursor->key()), toStringRef(cursor->value()));
accumulatedBytes += sizeof(KeyValueRef) + kv.expectedSize();
result->push_back_deep(result->arena(), kv);
KeyRef key = toStringRef(cursor->key());
ValueRef value = toStringRef(cursor->value());

accumulatedBytes += sizeof(KeyValueRef) + key.expectedSize() + value.expectedSize();
result->emplace_back_deep(result->arena(), key, value);
// Calling `cursor->Prev()` is potentially expensive, so short-circuit here just in case.
if (result->size() >= -rowLimit || accumulatedBytes >= byteLimit) {
break;
Expand Down