JoverZhang commented on code in PR #1681:
URL: https://github.com/apache/kvrocks/pull/1681#discussion_r1298602908
##########
src/types/redis_list.cc:
##########
@@ -392,6 +392,67 @@ rocksdb::Status List::Range(const Slice &user_key, int
start, int stop, std::vec
return rocksdb::Status::OK();
}
+rocksdb::Status List::Pos(const Slice &user_key, const Slice &elem, const
PosSpec &spec,
+ std::vector<int64_t> *indexes) {
+ assert(spec.rank != 0);
+ assert(!spec.count.has_value() || spec.count >= 0);
+ assert(spec.max_len >= 0);
+ indexes->clear();
+
+ std::string ns_key = AppendNamespacePrefix(user_key);
+ ListMetadata metadata(false);
+ rocksdb::Status s = GetMetadata(ns_key, &metadata);
+ if (!s.ok()) return s;
+
+ // A negative rank means start from the tail.
+ int64_t rank = spec.rank;
+ uint64_t start = metadata.head;
+ bool reversed = false;
+ if (rank < 0) {
+ rank = -rank;
+ start = metadata.tail - 1;
+ reversed = true;
+ }
+
+ std::string buf;
+ PutFixed64(&buf, start);
+ std::string start_key = InternalKey(ns_key, buf, metadata.version,
storage_->IsSlotIdEncoded()).Encode();
+ std::string prefix = InternalKey(ns_key, "", metadata.version,
storage_->IsSlotIdEncoded()).Encode();
+ std::string next_version_prefix = InternalKey(ns_key, "", metadata.version +
1, storage_->IsSlotIdEncoded()).Encode();
+
+ std::vector<uint64_t> to_delete_indexes;
+ rocksdb::ReadOptions read_options = storage_->DefaultScanOptions();
+ LatestSnapShot ss(storage_);
+ read_options.snapshot = ss.GetSnapShot();
+ rocksdb::Slice upper_bound(next_version_prefix);
+ read_options.iterate_upper_bound = &upper_bound;
+ rocksdb::Slice lower_bound(prefix);
+ read_options.iterate_lower_bound = &lower_bound;
+
+ auto list_len = static_cast<int64_t>(metadata.size);
+ int64_t max_len = spec.max_len;
+ int64_t count = spec.count.value_or(-1);
+ int64_t index = 0, matches = 0;
+
+ auto iter = util::UniqueIterator(storage_, read_options);
+ iter->Seek(start_key);
+ while (iter->Valid() && iter->key().starts_with(prefix) && (max_len == 0 ||
index < max_len)) {
+ if (iter->value() == elem) {
+ matches++;
+ if (matches >= rank) {
+ int64_t pos = !reversed ? index : list_len - index - 1;
+ indexes->push_back(pos);
+ if (count && matches - rank + 1 >= count) {
Review Comment:
Yeah, `count = -1 (by default)`. I took reference from Redis' implementation
of `LPOS` here. I did try removing this "trick" before, but I was never
successful, and it kinda feels flawless to me.
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