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fix(hset_family): Ensure empty hash sets are removed (#4873)

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When a search operation is performed on a hash set, expired fields are
removed as a side effect.

If at the end of such an operation the hash set becomes empty, its key
is removed from the database.

Signed-off-by: Abhijat Malviya <abhijat@dragonflydb.io>
This commit is contained in:
Abhijat Malviya 2025-04-09 12:25:43 +05:30 • committed by GitHub
parent 2d96a57edf
commit c129834cbf
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GPG key ID: B5690EEEBB952194
2 changed files with 104 additions and 26 deletions
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110
src/server/hset_family.cc
View file

@ -166,7 +166,7 @@ OpStatus IncrementValue(optional<string_view> prev_val, IncrByParam* param) {
param->emplace<int64_t>(new_val);
return OpStatus::OK;
};
}
OpStatus OpIncrBy(const OpArgs& op_args, string_view key, string_view field, IncrByParam* param) {
auto& db_slice = op_args.GetDbSlice();
@ -264,6 +264,62 @@ OpStatus OpIncrBy(const OpArgs& op_args, string_view key, string_view field, Inc
return OpStatus::OK;
}
struct KeyCleanup {
using CleanupFuncT = std::function<void(std::string_view)>;
explicit KeyCleanup(CleanupFuncT func, const std::string_view key_view)
: f{std::move(func)}, key{key_view} {
}
~KeyCleanup() {
if (armed) {
f(key);
}
}
void arm() {
armed = true;
}
CleanupFuncT f;
std::string key;
bool armed{false};
};
void DeleteKey(DbSlice& db_slice, const OpArgs& op_args, std::string_view key) {
if (auto del_it = db_slice.FindMutable(op_args.db_cntx, key, OBJ_HASH); del_it) {
del_it->post_updater.Run();
db_slice.Del(op_args.db_cntx, del_it->it);
if (op_args.shard->journal()) {
RecordJournal(op_args, "DEL"sv, {key});
}
}
}
std::pair<OpResult<DbSlice::ConstIterator>, KeyCleanup> FindReadOnly(DbSlice& db_slice,
const OpArgs& op_args,
std::string_view key) {
return std::pair{db_slice.FindReadOnly(op_args.db_cntx, key, OBJ_HASH),
KeyCleanup{[&](const auto& k) { DeleteKey(db_slice, op_args, k); }, key}};
}
// The find and contains functions perform the usual search on string maps, with the added argument
// KeyCleanup. This object is armed if the string map becomes empty during search due to keys being
// expired. An armed object on destruction removes the key which has just become empty.
StringMap::iterator Find(StringMap* sm, const std::string_view field, KeyCleanup& defer_cleanup) {
auto it = sm->Find(field);
if (sm->Empty()) {
defer_cleanup.arm();
}
return it;
}
bool Contains(StringMap* sm, const std::string_view field, KeyCleanup& defer_cleanup) {
auto result = sm->Contains(field);
if (sm->Empty()) {
defer_cleanup.arm();
}
return result;
}
OpResult<StringVec> OpScan(const OpArgs& op_args, std::string_view key, uint64_t* cursor,
const ScanOpts& scan_op) {
constexpr size_t HASH_TABLE_ENTRIES_FACTOR = 2; // return key/value
@ -274,7 +330,8 @@ OpResult<StringVec> OpScan(const OpArgs& op_args, std::string_view key, uint64_t
* of returning no or very few elements. (taken from redis code at db.c line 904 */
constexpr size_t INTERATION_FACTOR = 10;
auto find_res = op_args.GetDbSlice().FindReadOnly(op_args.db_cntx, key, OBJ_HASH);
DbSlice& db_slice = op_args.GetDbSlice();
auto [find_res, defer_cleanup] = FindReadOnly(db_slice, op_args, key);
if (!find_res) {
DVLOG(1) << "ScanOp: find failed: " << find_res << ", baling out";
@ -328,6 +385,10 @@ OpResult<StringVec> OpScan(const OpArgs& op_args, std::string_view key, uint64_t
do {
*cursor = sm->Scan(*cursor, scanCb);
} while (*cursor && max_iterations-- && res.size() < count);
if (sm->Empty()) {
defer_cleanup.arm();
}
}
return res;
@ -368,13 +429,15 @@ OpResult<uint32_t> OpDel(const OpArgs& op_args, string_view key, CmdArgList valu
StringMap* sm = GetStringMap(pv, op_args.db_cntx);
for (auto s : values) {
bool res = sm->Erase(ToSV(s));
if (res) {
if (sm->Erase(ToSV(s))) {
++deleted;
if (sm->UpperBoundSize() == 0) {
key_remove = true;
break;
}
}
// Even if the previous Erase op did not erase anything, it can remove expired fields as a
// side effect.
if (sm->Empty()) {
key_remove = true;
break;
}
}
}
@ -395,7 +458,7 @@ OpResult<vector<OptStr>> OpHMGet(const OpArgs& op_args, std::string_view key, Cm
DCHECK(!fields.empty());
auto& db_slice = op_args.GetDbSlice();
auto it_res = db_slice.FindReadOnly(op_args.db_cntx, key, OBJ_HASH);
auto [it_res, defer_cleanup] = FindReadOnly(db_slice, op_args, key);
if (!it_res)
return it_res.status();
@ -443,8 +506,7 @@ OpResult<vector<OptStr>> OpHMGet(const OpArgs& op_args, std::string_view key, Cm
StringMap* sm = GetStringMap(pv, op_args.db_cntx);
for (size_t i = 0; i < fields.size(); ++i) {
auto it = sm->Find(ToSV(fields[i]));
if (it != sm->end()) {
if (auto it = Find(sm, ToSV(fields[i]), defer_cleanup); it != sm->end()) {
result[i].emplace(it->second, sdslen(it->second));
}
}
@ -468,7 +530,7 @@ OpResult<uint32_t> OpLen(const OpArgs& op_args, string_view key) {
OpResult<int> OpExist(const OpArgs& op_args, string_view key, string_view field) {
auto& db_slice = op_args.GetDbSlice();
auto it_res = db_slice.FindReadOnly(op_args.db_cntx, key, OBJ_HASH);
auto [it_res, defer_cleanup] = FindReadOnly(db_slice, op_args, key);
if (!it_res) {
if (it_res.status() == OpStatus::KEY_NOTFOUND)
@ -486,13 +548,13 @@ OpResult<int> OpExist(const OpArgs& op_args, string_view key, string_view field)
DCHECK_EQ(kEncodingStrMap2, pv.Encoding());
StringMap* sm = GetStringMap(pv, op_args.db_cntx);
return sm->Contains(field) ? 1 : 0;
return Contains(sm, field, defer_cleanup) ? 1 : 0;
};
OpResult<string> OpGet(const OpArgs& op_args, string_view key, string_view field) {
auto& db_slice = op_args.GetDbSlice();
auto it_res = db_slice.FindReadOnly(op_args.db_cntx, key, OBJ_HASH);
auto [it_res, defer_cleanup] = FindReadOnly(db_slice, op_args, key);
if (!it_res)
return it_res.status();
@ -510,12 +572,11 @@ OpResult<string> OpGet(const OpArgs& op_args, string_view key, string_view field
DCHECK_EQ(pv.Encoding(), kEncodingStrMap2);
StringMap* sm = GetStringMap(pv, op_args.db_cntx);
auto it = sm->Find(field);
if (const auto it = Find(sm, field, defer_cleanup); it != sm->end()) {
return string(it->second, sdslen(it->second));
}
if (it == sm->end())
return OpStatus::KEY_NOTFOUND;
return string(it->second, sdslen(it->second));
return OpStatus::KEY_NOTFOUND;
}
OpResult<vector<string>> OpGetAll(const OpArgs& op_args, string_view key, uint8_t mask) {
@ -570,10 +631,7 @@ OpResult<vector<string>> OpGetAll(const OpArgs& op_args, string_view key, uint8_
// and the enconding is guaranteed to be a DenseSet since we only support expiring
// value with that enconding.
if (res.empty()) {
// post_updater will run immediately
auto it = db_slice.FindMutable(op_args.db_cntx, key).it;
db_slice.Del(op_args.db_cntx, it);
DeleteKey(db_slice, op_args, key);
}
return res;
@ -581,7 +639,7 @@ OpResult<vector<string>> OpGetAll(const OpArgs& op_args, string_view key, uint8_
OpResult<size_t> OpStrLen(const OpArgs& op_args, string_view key, string_view field) {
auto& db_slice = op_args.GetDbSlice();
auto it_res = db_slice.FindReadOnly(op_args.db_cntx, key, OBJ_HASH);
auto [it_res, defer_cleanup] = FindReadOnly(db_slice, op_args, key);
if (!it_res) {
if (it_res.status() == OpStatus::KEY_NOTFOUND)
@ -601,7 +659,7 @@ OpResult<size_t> OpStrLen(const OpArgs& op_args, string_view key, string_view fi
DCHECK_EQ(pv.Encoding(), kEncodingStrMap2);
StringMap* sm = GetStringMap(pv, op_args.db_cntx);
auto it = sm->Find(field);
auto it = Find(sm, field, defer_cleanup);
return it != sm->end() ? sdslen(it->second) : 0;
}

20
src/server/hset_family_test.cc
View file

@ -521,4 +521,24 @@ TEST_F(HSetFamilyTest, ScanAfterExpireSet) {
EXPECT_THAT(vec, Contains("avalue").Times(1));
}
TEST_F(HSetFamilyTest, KeyRemovedWhenEmpty) {
auto test_cmd = [&](const std::function<void()>& f, const std::string_view tag) {
EXPECT_THAT(Run({"HSET", "a", "afield", "avalue"}), IntArg(1));
EXPECT_THAT(Run({"HEXPIRE", "a", "1", "FIELDS", "1", "afield"}), IntArg(1));
AdvanceTime(1000);
EXPECT_THAT(Run({"EXISTS", "a"}), IntArg(1));
f();
EXPECT_THAT(Run({"EXISTS", "a"}), IntArg(0)) << "failed when testing " << tag;
};
test_cmd([&] { EXPECT_THAT(Run({"HGET", "a", "afield"}), ArgType(RespExpr::NIL)); }, "HGET");
test_cmd([&] { EXPECT_THAT(Run({"HGETALL", "a"}), RespArray(ElementsAre())); }, "HGETALL");
test_cmd([&] { EXPECT_THAT(Run({"HDEL", "a", "afield"}), IntArg(0)); }, "HDEL");
test_cmd([&] { EXPECT_THAT(Run({"HSCAN", "a", "0"}).GetVec()[0], "0"); }, "HSCAN");
test_cmd([&] { EXPECT_THAT(Run({"HMGET", "a", "afield"}), ArgType(RespExpr::NIL)); }, "HMGET");
test_cmd([&] { EXPECT_THAT(Run({"HEXISTS", "a", "afield"}), IntArg(0)); }, "HEXISTS");
test_cmd([&] { EXPECT_THAT(Run({"HSTRLEN", "a", "afield"}), IntArg(0)); }, "HSTRLEN");
}
} // namespace dfly