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fix: support dump for external objects #4794

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merged 1 commit into from
Mar 18, 2025
Merged

fix: support dump for external objects #4794

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18 changes: 16 additions & 2 deletions src/server/generic_family.cc
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Original file line number Diff line number Diff line change
Expand Up @@ -31,7 +31,9 @@ extern "C" {
#include "server/rdb_save.h"
#include "server/search/doc_index.h"
#include "server/set_family.h"
#include "server/tiered_storage.h"
#include "server/transaction.h"
#include "util/fibers/future.h"
#include "util/varz.h"

ABSL_FLAG(uint32_t, dbnum, 16, "Number of databases");
Expand Down Expand Up @@ -524,9 +526,21 @@ OpResult<std::string> OpDump(const OpArgs& op_args, string_view key) {
if (IsValid(it)) {
DVLOG(1) << "Dump: key '" << key << "' successfully found, going to dump it";
io::StringSink sink;
SerializerBase::DumpObject(it->second, &sink);
return sink.str(); // TODO: Add rvalue overload to str()
const PrimeValue& pv = it->second;

if (pv.IsExternal() && !pv.IsCool()) {
util::fb2::Future<string> future =
op_args.shard->tiered_storage()->Read(op_args.db_cntx.db_index, key, pv);

CompactObj co(future.Get());
SerializerBase::DumpObject(co, &sink);
} else {
SerializerBase::DumpObject(it->second, &sink);
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@adiholden adiholden Mar 18, 2025 •
edited
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What is this cool thingy I dont remember this...

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it is very cool, actually. When we offload an object we may still keep it in-memory so if we hit it later, we can warm it up without hitting disk by moving it from the cool storage. Cool storage is just a FIFO queue of items and if we become low on memory we start discarding the oldest ones, making the values fully external.

}

return std::move(sink).str();
}

// fallback
DVLOG(1) << "Dump: '" << key << "' Not found";
return OpStatus::KEY_NOTFOUND;
Expand Down
9 changes: 8 additions & 1 deletion src/server/rdb_save.cc
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Expand Up @@ -243,7 +243,14 @@ std::error_code RdbSerializer::SaveValue(const PrimeValue& pv) {
if (opt_int) {
ec = SaveLongLongAsString(*opt_int);
} else {
ec = SaveString(pv.GetSlice(&tmp_str_));
if (pv.IsExternal()) {
if (pv.IsCool()) {
return SaveValue(pv.GetCool().record->value);
}
LOG(FATAL) << "External string not supported yet";
} else {
ec = SaveString(pv.GetSlice(&tmp_str_));
}
}
} else {
ec = SaveObject(pv);
Expand Down
5 changes: 2 additions & 3 deletions src/server/snapshot.cc
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Expand Up @@ -389,9 +389,8 @@ void SliceSnapshot::SerializeExternal(DbIndex db_index, PrimeKey key, const Prim
time_t expire_time, uint32_t mc_flags) {
// We prefer avoid blocking, so we just schedule a tiered read and append
// it to the delayed entries.
util::fb2::Future<string> future;
auto cb = [future](const std::string& v) mutable { future.Resolve(v); };
EngineShard::tlocal()->tiered_storage()->Read(db_index, key.ToString(), pv, std::move(cb));
util::fb2::Future<string> future =
EngineShard::tlocal()->tiered_storage()->Read(db_index, key.ToString(), pv);

delayed_entries_.push_back({db_index, std::move(key), std::move(future), expire_time, mc_flags});
++type_freq_map_[RDB_TYPE_STRING];
Expand Down
20 changes: 20 additions & 0 deletions src/server/tiered_storage_test.cc
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Expand Up @@ -355,4 +355,24 @@ TEST_F(TieredStorageTest, SetExistingExpire) {
}
}

TEST_F(TieredStorageTest, Dump) {
absl::FlagSaver saver;
SetFlag(&FLAGS_tiered_offload_threshold, 0.0f); // offload all values

// we want to test without cooling to trigger disk I/O on reads.
SetFlag(&FLAGS_tiered_experimental_cooling, false);

const int kNum = 10;
for (size_t i = 0; i < kNum; i++) {
Run({"SET", absl::StrCat("k", i), BuildString(3000)}); // big enough to trigger offloading.
}

ExpectConditionWithinTimeout([&] { return GetMetrics().tiered_stats.total_stashes == kNum; });

auto resp = Run({"DUMP", "k0"});
EXPECT_THAT(Run({"del", "k0"}), IntArg(1));
resp = Run({"restore", "k0", "0", facade::ToSV(resp.GetBuf())});
EXPECT_EQ(resp, "OK");
}

} // namespace dfly
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