Summary:
Currently, when the block cache is used for the filter block, it is not
really the block itself that is stored in the cache but a FilterBlockReader
object. Since this object is not pure data (it has, for instance, pointers that
might dangle, including in one case a back pointer to the TableReader), it's not
really sharable. To avoid the issues around this, the current code erases the
cache entries when the TableReader is closed (which, BTW, is not sufficient
since a concurrent TableReader might have picked up the object in the meantime).
Instead of doing this, the patch moves the FilterBlockReader out of the cache
altogether, and decouples the filter reader object from the filter block.
In particular, instead of the TableReader owning, or caching/pinning the
FilterBlockReader (based on the customer's settings), with the change the
TableReader unconditionally owns the FilterBlockReader, which in turn
owns/caches/pins the filter block. This change also enables us to reuse the code
paths historically used for data blocks for filters as well.
Note:
Eviction statistics for filter blocks are temporarily broken. We plan to fix this in a
separate phase.
Pull Request resolved: https://github.com/facebook/rocksdb/pull/5504
Test Plan: make asan_check
Differential Revision: D16036974
Pulled By: ltamasi
fbshipit-source-id: 770f543c5fb4ed126fd1e04bfd3809cf4ff9c091
Summary:
CachableEntry is used in a variety of contexts: it may refer to a cached
object (i.e. an object in the block cache), an owned object, or an
unowned object; also, in some cases (most notably with iterators), the
responsibility of managing the pointed-to object gets handed off to
another object. Each of the above scenarios have different implications
for the lifecycle of the referenced object. For the most part, the patch
does not change the lifecycle of managed objects; however, it makes
these relationships explicit, and it also enables us to eliminate some
hacks and accident-prone code around releasing cache handles and
deleting/cleaning up objects. (The only places where the patch changes
how an objects are managed are the partitions of partitioned indexes and
filters.)
Pull Request resolved: https://github.com/facebook/rocksdb/pull/5252
Differential Revision: D15101358
Pulled By: ltamasi
fbshipit-source-id: 9eb59e9ae5a7230e3345789762d0ba1f189485be
Levi Tamasi