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# Description Gather most of the scattered `redisDb`-related code from the per-slot dict PR (#11695) and turn it to a new data structure, `kvstore`. i.e. it's a class that represents an array of dictionaries. # Motivation The main motivation is code cleanliness, the idea of using an array of dictionaries is very well-suited to becoming a self-contained data structure. This allowed cleaning some ugly code, among others: loops that run twice on the main dict and expires dict, and duplicate code for allocating and releasing this data structure. # Notes 1. This PR reverts the part of https://github.com/redis/redis/pull/12848 where the `rehashing` list is global (handling rehashing `dict`s is under the responsibility of `kvstore`, and should not be managed by the server) 2. This PR also replaces the type of `server.pubsubshard_channels` from `dict**` to `kvstore` (original PR: https://github.com/redis/redis/pull/12804). After that was done, server.pubsub_channels was also chosen to be a `kvstore` (with only one `dict`, which seems odd) just to make the code cleaner by making it the same type as `server.pubsubshard_channels`, see `pubsubtype.serverPubSubChannels` 3. the keys and expires kvstores are currenlty configured to allocate the individual dicts only when the first key is added (unlike before, in which they allocated them in advance), but they won't release them when the last key is deleted. Worth mentioning that due to the recent change the reply of DEBUG HTSTATS changed, in case no keys were ever added to the db. before: ``` 127.0.0.1:6379> DEBUG htstats 9 [Dictionary HT] Hash table 0 stats (main hash table): No stats available for empty dictionaries [Expires HT] Hash table 0 stats (main hash table): No stats available for empty dictionaries ``` after: ``` 127.0.0.1:6379> DEBUG htstats 9 [Dictionary HT] [Expires HT] ```