Ensure that all in-memory records are checkpointed when not using --storage-tier #117
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Currently, a snapshot checkpoint in Tsavorite only takes a copy of records in mutable region (90% of memory) by default, since earlier records are expected to be flushed to disk and therefore available after recovery.
But when Garnet is configured to run as a cache, i.e., entirely in main memory, there is no backing device (rather, the backing device is a
NullDevice).This PR proposes for a snapshot checkpoint to include the immutable region of memory in this case. This will ensure that DBSIZE of Garnet in "cache mode" (i.e., not using
--storage-tier) before aSAVEand after a restart with--recoverwill be the same. That is, we will not lose the cache entries in the immutable region of memory.