Yanqin Jin cd72f8974b Allow mutex to be released in GetAggregatedIntProperty (#7412)
Summary:
Current implementation holds db mutex while calling
`GetAggregatedIntProperty()`. For property kEstimateTableReadersMem,
this can be expensive, especially if the number of table readers is
high.
We can release and re-acquire db mutex if
property_info.need_out_of_mutex is true.

Pull Request resolved: https://github.com/facebook/rocksdb/pull/7412

Test Plan:
make check
COMPILE_WITH_ASAN=1 make check
COMPILE_WITH_TSAN=1 make check
Also test internally on a shadow host. Used bpf to verify the
excessively long db mutex holding no longer exists when applications
call GetApproximateMemoryUsageByType().

Reviewed By: jay-zhuang

Differential Revision: D23794824

Pulled By: riversand963

fbshipit-source-id: 6bc02a59fd25613d343a62cf817467c7122c9721
2020-09-22 12:37:16 -07:00
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