Add overhead of all DBs and rehashing dict count to info. (#12913)
Sometimes we need to make fast judgement about why Redis is suddenly taking more memory. One of the reasons is main DB's dicts doing rehashing. We may use `MEMORY STATS` to monitor the overhead memory of each DB, but there still lacks a total sum to show an overall trend. So this PR adds the total overhead of all DBs to `INFO MEMORY` section, together with the total count of rehashing DB dicts, providing some intuitive metrics about main dicts rehashing. This PR adds the following metrics to INFO MEMORY * `mem_overhead_db_hashtable_rehashing` - only size of ht[0] in dictionaries we're rehashing (i.e. the memory that's gonna get released soon) and a similar ones to MEMORY STATS: * `overhead.db.hashtable.lut` (complements the existing `overhead.hashtable.main` and `overhead.hashtable.expires` which also counts the `dictEntry` structs too) * `overhead.db.hashtable.rehashing` - temporary rehashing overhead. * `db.dict.rehashing.count` - number of top level dictionaries being rehashed. --------- Co-authored-by:zhaozhao.zz <zhaozhao.zz@alibaba-inc.com> Co-authored-by:
Oran Agra <oran@redislabs.com>
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