16 Commits (b7747bbc9f49761b75ae6ae2bdaebda960cda37d)

Author	SHA1	Message	Date
Peter Dillinger	9f7801c5f1	Major Cache refactoring, CPU efficiency improvement (#10975) ... Summary: This is several refactorings bundled into one to avoid having to incrementally re-modify uses of Cache several times. Overall, there are breaking changes to Cache class, and it becomes more of low-level interface for implementing caches, especially block cache. New internal APIs make using Cache cleaner than before, and more insulated from block cache evolution. Hopefully, this is the last really big block cache refactoring, because of rather effectively decoupling the implementations from the uses. This change also removes the EXPERIMENTAL designation on the SecondaryCache support in Cache. It seems reasonably mature at this point but still subject to change/evolution (as I warn in the API docs for Cache). The high-level motivation for this refactoring is to minimize code duplication / compounding complexity in adding SecondaryCache support to HyperClockCache (in a later PR). Other benefits listed below. * static_cast lines of code +29 -35 (net removed 6) * reinterpret_cast lines of code +6 -32 (net removed 26) ## cache.h and secondary_cache.h * Always use CacheItemHelper with entries instead of just a Deleter. There are several motivations / justifications: * Simpler for implementations to deal with just one Insert and one Lookup. * Simpler and more efficient implementation because we don't have to track which entries are using helpers and which are using deleters * Gets rid of hack to classify cache entries by their deleter. Instead, the CacheItemHelper includes a CacheEntryRole. This simplifies a lot of code (cache_entry_roles.h almost eliminated). Fixes https://github.com/facebook/rocksdb/issues/9428. * Makes it trivial to adjust SecondaryCache behavior based on kind of block (e.g. don't re-compress filter blocks). * It is arguably less convenient for many direct users of Cache, but direct users of Cache are now rare with introduction of typed_cache.h (below). * I considered and rejected an alternative approach in which we reduce customizability by assuming each secondary cache compatible value starts with a Slice referencing the uncompressed block contents (already true or mostly true), but we apparently intend to stack secondary caches. Saving an entry from a compressed secondary to a lower tier requires custom handling offered by SaveToCallback, etc. * Make CreateCallback part of the helper and introduce CreateContext to work with it (alternative to https://github.com/facebook/rocksdb/issues/10562). This cleans up the interface while still allowing context to be provided for loading/parsing values into primary cache. This model works for async lookup in BlockBasedTable reader (reader owns a CreateContext) under the assumption that it always waits on secondary cache operations to finish. (Otherwise, the CreateContext could be destroyed while async operation depending on it continues.) This likely contributes most to the observed performance improvement because it saves an std::function backed by a heap allocation. * Use char* for serialized data, e.g. in SaveToCallback, where void* was confusingly used. (We use `char*` for serialized byte data all over RocksDB, with many advantages over `void*`. `memcpy` etc. are legacy APIs that should not be mimicked.) * Add a type alias Cache::ObjectPtr = void*, so that we can better indicate the intent of the void* when it is to be the object associated with a Cache entry. Related: started (but did not complete) a refactoring to move away from "value" of a cache entry toward "object" or "obj". (It is confusing to call Cache a key-value store (like DB) when it is really storing arbitrary in-memory objects, not byte strings.) * Remove unnecessary key param from DeleterFn. This is good for efficiency in HyperClockCache, which does not directly store the cache key in memory. (Alternative to https://github.com/facebook/rocksdb/issues/10774) * Add allocator to Cache DeleterFn. This is a kind of future-proofing change in case we get more serious about using the Cache allocator for memory tracked by the Cache. Right now, only the uncompressed block contents are allocated using the allocator, and a pointer to that allocator is saved as part of the cached object so that the deleter can use it. (See CacheAllocationPtr.) If in the future we are able to "flatten out" our Cache objects some more, it would be good not to have to track the allocator as part of each object. * Removes legacy `ApplyToAllCacheEntries` and changes `ApplyToAllEntries` signature for Deleter->CacheItemHelper change. ## typed_cache.h Adds various "typed" interfaces to the Cache as internal APIs, so that most uses of Cache can use simple type safe code without casting and without explicit deleters, etc. Almost all of the non-test, non-glue code uses of Cache have been migrated. (Follow-up work: CompressedSecondaryCache deserves deeper attention to migrate.) This change expands RocksDB's internal usage of metaprogramming and SFINAE (https://en.cppreference.com/w/cpp/language/sfinae). The existing usages of Cache are divided up at a high level into these new interfaces. See updated existing uses of Cache for examples of how these are used. * PlaceholderCacheInterface - Used for making cache reservations, with entries that have a charge but no value. * BasicTypedCacheInterface<TValue> - Used for primary cache storage of objects of type TValue, which can be cleaned up with std::default_delete<TValue>. The role is provided by TValue::kCacheEntryRole or given in an optional template parameter. * FullTypedCacheInterface<TValue, TCreateContext> - Used for secondary cache compatible storage of objects of type TValue. In addition to BasicTypedCacheInterface constraints, we require TValue::ContentSlice() to return persistable data. This simplifies usage for the normal case of simple secondary cache compatibility (can give you a Slice to the data already in memory). In addition to TCreateContext performing the role of Cache::CreateContext, it is also expected to provide a factory function for creating TValue. * For each of these, there's a "Shared" version (e.g. FullTypedSharedCacheInterface) that holds a shared_ptr to the Cache, rather than assuming external ownership by holding only a raw `Cache*`. These interfaces introduce specific handle types for each interface instantiation, so that it's easy to see what kind of object is controlled by a handle. (Ultimately, this might not be worth the extra complexity, but it seems OK so far.) Note: I attempted to make the cache 'charge' automatically inferred from the cache object type, such as by expecting an ApproximateMemoryUsage() function, but this is not so clean because there are cases where we need to compute the charge ahead of time and don't want to re-compute it. ## block_cache.h This header is essentially the replacement for the old block_like_traits.h. It includes various things to support block cache access with typed_cache.h for block-based table. ## block_based_table_reader.cc Before this change, accessing the block cache here was an awkward mix of static polymorphism (template TBlocklike) and switch-case on a dynamic BlockType value. This change mostly unifies on static polymorphism, relying on minor hacks in block_cache.h to distinguish variants of Block. We still check BlockType in some places (especially for stats, which could be improved in follow-up work) but at least the BlockType is a static constant from the template parameter. (No more awkward partial redundancy between static and dynamic info.) This likely contributes to the overall performance improvement, but hasn't been tested in isolation. The other key source of simplification here is a more unified system of creating block cache objects: for directly populating from primary cache and for promotion from secondary cache. Both use BlockCreateContext, for context and for factory functions. ## block_based_table_builder.cc, cache_dump_load_impl.cc Before this change, warming caches was super ugly code. Both of these source files had switch statements to basically transition from the dynamic BlockType world to the static TBlocklike world. None of that mess is needed anymore as there's a new, untyped WarmInCache function that handles all the details just as promotion from SecondaryCache would. (Fixes `TODO akanksha: Dedup below code` in block_based_table_builder.cc.) ## Everything else Mostly just updating Cache users to use new typed APIs when reasonably possible, or changed Cache APIs when not. Pull Request resolved: https://github.com/facebook/rocksdb/pull/10975 Test Plan: tests updated Performance test setup similar to https://github.com/facebook/rocksdb/issues/10626 (by cache size, LRUCache when not "hyper" for HyperClockCache): 34MB 1thread base.hyper -> kops/s: 0.745 io_bytes/op: 2.52504e+06 miss_ratio: 0.140906 max_rss_mb: 76.4844 34MB 1thread new.hyper -> kops/s: 0.751 io_bytes/op: 2.5123e+06 miss_ratio: 0.140161 max_rss_mb: 79.3594 34MB 1thread base -> kops/s: 0.254 io_bytes/op: 1.36073e+07 miss_ratio: 0.918818 max_rss_mb: 45.9297 34MB 1thread new -> kops/s: 0.252 io_bytes/op: 1.36157e+07 miss_ratio: 0.918999 max_rss_mb: 44.1523 34MB 32thread base.hyper -> kops/s: 7.272 io_bytes/op: 2.88323e+06 miss_ratio: 0.162532 max_rss_mb: 516.602 34MB 32thread new.hyper -> kops/s: 7.214 io_bytes/op: 2.99046e+06 miss_ratio: 0.168818 max_rss_mb: 518.293 34MB 32thread base -> kops/s: 3.528 io_bytes/op: 1.35722e+07 miss_ratio: 0.914691 max_rss_mb: 264.926 34MB 32thread new -> kops/s: 3.604 io_bytes/op: 1.35744e+07 miss_ratio: 0.915054 max_rss_mb: 264.488 233MB 1thread base.hyper -> kops/s: 53.909 io_bytes/op: 2552.35 miss_ratio: 0.0440566 max_rss_mb: 241.984 233MB 1thread new.hyper -> kops/s: 62.792 io_bytes/op: 2549.79 miss_ratio: 0.044043 max_rss_mb: 241.922 233MB 1thread base -> kops/s: 1.197 io_bytes/op: 2.75173e+06 miss_ratio: 0.103093 max_rss_mb: 241.559 233MB 1thread new -> kops/s: 1.199 io_bytes/op: 2.73723e+06 miss_ratio: 0.10305 max_rss_mb: 240.93 233MB 32thread base.hyper -> kops/s: 1298.69 io_bytes/op: 2539.12 miss_ratio: 0.0440307 max_rss_mb: 371.418 233MB 32thread new.hyper -> kops/s: 1421.35 io_bytes/op: 2538.75 miss_ratio: 0.0440307 max_rss_mb: 347.273 233MB 32thread base -> kops/s: 9.693 io_bytes/op: 2.77304e+06 miss_ratio: 0.103745 max_rss_mb: 569.691 233MB 32thread new -> kops/s: 9.75 io_bytes/op: 2.77559e+06 miss_ratio: 0.103798 max_rss_mb: 552.82 1597MB 1thread base.hyper -> kops/s: 58.607 io_bytes/op: 1449.14 miss_ratio: 0.0249324 max_rss_mb: 1583.55 1597MB 1thread new.hyper -> kops/s: 69.6 io_bytes/op: 1434.89 miss_ratio: 0.0247167 max_rss_mb: 1584.02 1597MB 1thread base -> kops/s: 60.478 io_bytes/op: 1421.28 miss_ratio: 0.024452 max_rss_mb: 1589.45 1597MB 1thread new -> kops/s: 63.973 io_bytes/op: 1416.07 miss_ratio: 0.0243766 max_rss_mb: 1589.24 1597MB 32thread base.hyper -> kops/s: 1436.2 io_bytes/op: 1357.93 miss_ratio: 0.0235353 max_rss_mb: 1692.92 1597MB 32thread new.hyper -> kops/s: 1605.03 io_bytes/op: 1358.04 miss_ratio: 0.023538 max_rss_mb: 1702.78 1597MB 32thread base -> kops/s: 280.059 io_bytes/op: 1350.34 miss_ratio: 0.023289 max_rss_mb: 1675.36 1597MB 32thread new -> kops/s: 283.125 io_bytes/op: 1351.05 miss_ratio: 0.0232797 max_rss_mb: 1703.83 Almost uniformly improving over base revision, especially for hot paths with HyperClockCache, up to 12% higher throughput seen (1597MB, 32thread, hyper). The improvement for that is likely coming from much simplified code for providing context for secondary cache promotion (CreateCallback/CreateContext), and possibly from less branching in block_based_table_reader. And likely a small improvement from not reconstituting key for DeleterFn. Reviewed By: anand1976 Differential Revision: D42417818 Pulled By: pdillinger fbshipit-source-id: f86bfdd584dce27c028b151ba56818ad14f7a432	2 years ago
Levi Tamasi	fe56cb9aa0	Eliminate some allocations/copies around the blob cache (#10647) ... Summary: Historically, `BlobFileReader` has returned the blob(s) read from the file in the `PinnableSlice` provided by the client. This interface was preserved when caching was implemented for blobs, which meant that the blob data was copied multiple times when caching was in use: first, into the client-provided `PinnableSlice` (by `BlobFileReader::SaveValue`), and then, into the object stored in the cache (by `BlobSource::PutBlobIntoCache`). The patch eliminates these copies and the related allocations by changing `BlobFileReader` so it returns its results in the form of heap-allocated `BlobContents` objects that can be directly inserted into the cache. The allocations backing these `BlobContents` objects are made using the blob cache's allocator if the blobs are to be inserted into the cache (i.e. if a cache is configured and the `fill_cache` read option is set). Note: this PR focuses on the common case when blobs are compressed; some further small optimizations are possible for uncompressed blobs. Pull Request resolved: https://github.com/facebook/rocksdb/pull/10647 Test Plan: `make check` Reviewed By: riversand963 Differential Revision: D39335185 Pulled By: ltamasi fbshipit-source-id: 464503d60a5520d654c8273ffb8efd5d1bcd7b36	2 years ago
Levi Tamasi	b07217da04	Pin the newly cached blob after insert (#10625) ... Summary: With the current code, when a blob isn't found in the cache and gets read from the blob file and then inserted into the cache, the application gets passed the self-contained `PinnableSlice` resulting from the blob file read. The patch changes this so that the `PinnableSlice` pins the cache entry instead in this case. Pull Request resolved: https://github.com/facebook/rocksdb/pull/10625 Test Plan: `make check` Reviewed By: pdillinger Differential Revision: D39220904 Pulled By: ltamasi fbshipit-source-id: cb9c62881e3523b1e9f614e00bf503bac2fe3b0a	2 years ago
Levi Tamasi	23376aa576	Improve the accounting of memory used by cached blobs (#10583) ... Summary: The patch improves the bookkeeping around the memory usage of cached blobs in two ways: 1) it uses `malloc_usable_size`, which accounts for allocator bin sizes etc., and 2) it also considers the memory usage of the `BlobContents` object in addition to the blob itself. Note: some unit tests had been relying on the cache charge being equal to the size of the cached blob; these were updated. Pull Request resolved: https://github.com/facebook/rocksdb/pull/10583 Test Plan: `make check` Reviewed By: riversand963 Differential Revision: D39060680 Pulled By: ltamasi fbshipit-source-id: 3583adce2b4ce6e84861f3fadccbfd2e5a3cc482	2 years ago
Levi Tamasi	3f57d84af4	Introduce a dedicated class to represent blob values (#10571) ... Summary: The patch introduces a new class called `BlobContents`, which represents a single uncompressed blob value. We currently use `std::string` for this purpose; `BlobContents` is somewhat smaller but the primary reason for a dedicated class is that it enables certain improvements and optimizations like eliding a copy when inserting a blob into the cache, using custom allocators, or more control over and better accounting of the memory usage of cached blobs (see https://github.com/facebook/rocksdb/issues/10484). (We plan to implement these in subsequent PRs.) Pull Request resolved: https://github.com/facebook/rocksdb/pull/10571 Test Plan: `make check` Reviewed By: riversand963 Differential Revision: D39000965 Pulled By: ltamasi fbshipit-source-id: f296eddf9dec4fc3e11cad525b462bdf63c78f96	2 years ago
Peter Dillinger	86a1e3e0e7	Derive cache keys from SST unique IDs (#10394) ... Summary: ... so that cache keys can be derived from DB manifest data before reading the file from storage--so that every part of the file can potentially go in a persistent cache. See updated comments in cache_key.cc for technical details. Importantly, the new cache key encoding uses some fancy but efficient math to pack data into the cache key without depending on the sizes of the various pieces. This simplifies some existing code creating cache keys, like cache warming before the file size is known. This should provide us an essentially permanent mapping between SST unique IDs and base cache keys, with the ability to "upgrade" SST unique IDs (and thus cache keys) with new SST format_versions. These cache keys are of similar, perhaps indistinguishable quality to the previous generation. Before this change (see "corrected" days between collision): ``` ./cache_bench -stress_cache_key -sck_keep_bits=43 18 collisions after 2 x 90 days, est 10 days between (1.15292e+19 corrected) ``` After this change (keep 43 bits, up through 50, to validate "trajectory" is ok on "corrected" days between collision): ``` 19 collisions after 3 x 90 days, est 14.2105 days between (1.63836e+19 corrected) 16 collisions after 5 x 90 days, est 28.125 days between (1.6213e+19 corrected) 15 collisions after 7 x 90 days, est 42 days between (1.21057e+19 corrected) 15 collisions after 17 x 90 days, est 102 days between (1.46997e+19 corrected) 15 collisions after 49 x 90 days, est 294 days between (2.11849e+19 corrected) 15 collisions after 62 x 90 days, est 372 days between (1.34027e+19 corrected) 15 collisions after 53 x 90 days, est 318 days between (5.72858e+18 corrected) 15 collisions after 309 x 90 days, est 1854 days between (1.66994e+19 corrected) ``` However, the change does modify (probably weaken) the "guaranteed unique" promise from this > SST files generated in a single process are guaranteed to have unique cache keys, unless/until number session ids * max file number = 2**86 to this (see https://github.com/facebook/rocksdb/issues/10388) > With the DB id limitation, we only have nice guaranteed unique cache keys for files generated in a single process until biggest session_id_counter and offset_in_file reach combined 64 bits I don't think this is a practical concern, though. Pull Request resolved: https://github.com/facebook/rocksdb/pull/10394 Test Plan: unit tests updated, see simulation results above Reviewed By: jay-zhuang Differential Revision: D38667529 Pulled By: pdillinger fbshipit-source-id: 49af3fe7f47e5b61162809a78b76c769fd519fba	2 years ago
Gang Liao	0b6bc101ba	Charge blob cache usage against the global memory limit (#10321) ... Summary: To help service owners to manage their memory budget effectively, we have been working towards counting all major memory users inside RocksDB towards a single global memory limit (see e.g. https://github.com/facebook/rocksdb/wiki/Write-Buffer-Manager#cost-memory-used-in-memtable-to-block-cache). The global limit is specified by the capacity of the block-based table's block cache, and is technically implemented by inserting dummy entries ("reservations") into the block cache. The goal of this task is to support charging the memory usage of the new blob cache against this global memory limit when the backing cache of the blob cache and the block cache are different. This PR is a part of https://github.com/facebook/rocksdb/issues/10156 Pull Request resolved: https://github.com/facebook/rocksdb/pull/10321 Reviewed By: ltamasi Differential Revision: D37913590 Pulled By: gangliao fbshipit-source-id: eaacf23907f82dc7d18964a3f24d7039a2937a72	2 years ago
Gang Liao	95ef007adc	Support using secondary cache with the blob cache (#10349) ... Summary: RocksDB supports a two-level cache hierarchy (see https://rocksdb.org/blog/2021/05/27/rocksdb-secondary-cache.html), where items evicted from the primary cache can be spilled over to the secondary cache, or items from the secondary cache can be promoted to the primary one. We have a CacheLib-based non-volatile secondary cache implementation that can be used to improve read latencies and reduce the amount of network bandwidth when using distributed file systems. In addition, we have recently implemented a compressed secondary cache that can be used as a replacement for the OS page cache when e.g. direct I/O is used. The goals of this task are to add support for using a secondary cache with the blob cache and to measure the potential performance gains using `db_bench`. This task is a part of https://github.com/facebook/rocksdb/issues/10156 Pull Request resolved: https://github.com/facebook/rocksdb/pull/10349 Reviewed By: ltamasi Differential Revision: D37896773 Pulled By: gangliao fbshipit-source-id: 7804619ce4a44b73d9e11ad606640f9385969c84	2 years ago
Gang Liao	c987eb4712	Eliminate the copying of blobs when serving reads from the cache (#10297) ... Summary: The blob cache enables an optimization on the read path: when a blob is found in the cache, we can avoid copying it into the buffer provided by the application. Instead, we can simply transfer ownership of the cache handle to the target `PinnableSlice`. (Note: this relies on the `Cleanable` interface, which is implemented by `PinnableSlice`.) This has the potential to save a lot of CPU, especially with large blob values. This task is a part of https://github.com/facebook/rocksdb/issues/10156 Pull Request resolved: https://github.com/facebook/rocksdb/pull/10297 Reviewed By: riversand963 Differential Revision: D37640311 Pulled By: gangliao fbshipit-source-id: 92de0e35cc703d06c87c5c1861cc2899ec52234a	3 years ago
Gang Liao	056e08d6c4	Enable blob caching for MultiGetBlob in RocksDB (#10272) ... Summary: - [x] Enabled blob caching for MultiGetBlob in RocksDB - [x] Refactored MultiGetBlob logic and interface in RocksDB - [x] Cleaned up Version::MultiGetBlob() and moved 'blob'-related code snippets into BlobSource - [x] Add End-to-end test cases in db_blob_basic_test and also add unit tests in blob_source_test This task is a part of https://github.com/facebook/rocksdb/issues/10156 Pull Request resolved: https://github.com/facebook/rocksdb/pull/10272 Reviewed By: ltamasi Differential Revision: D37558112 Pulled By: gangliao fbshipit-source-id: a73a6a94ffdee0024d5b2a39e6d1c1a7d38664db	3 years ago
Gang Liao	d7ebb58cb5	Add blob cache tickers, perf context statistics, and DB properties (#10203) ... Summary: In order to be able to monitor the performance of the new blob cache, we made the follow changes: - Add blob cache hit/miss/insertion tickers (see https://github.com/facebook/rocksdb/wiki/Statistics) - Extend the perf context similarly (see https://github.com/facebook/rocksdb/wiki/Perf-Context-and-IO-Stats-Context) - Implement new DB properties (see e.g. https://github.com/facebook/rocksdb/blob/main/include/rocksdb/db.h#L1042-L1051) that expose the capacity and current usage of the blob cache. This PR is a part of https://github.com/facebook/rocksdb/issues/10156 Pull Request resolved: https://github.com/facebook/rocksdb/pull/10203 Reviewed By: ltamasi Differential Revision: D37478658 Pulled By: gangliao fbshipit-source-id: d8ee3f41d47315ef725e4551226330b4b6832e40	3 years ago
Gang Liao	a1eb02f089	Change the semantics of bytes_read in GetBlob/MultiGetBlob for consistency (#10248) ... Summary: The `bytes_read` returned by the current BlobSource interface is ambiguous. The uncompressed blob size is returned if the cache hits. The size of the blob read from disk, presumably the compressed version, is returned if the cache misses. Two differing semantics might cause ambiguity and consistency issues. For example, this inconsistency causes the assertion failure (T124246362 and its hot fix is https://github.com/facebook/rocksdb/issues/10249). This goal is to require that the value of `byte read` always be an on-disk blob record size. Pull Request resolved: https://github.com/facebook/rocksdb/pull/10248 Reviewed By: ltamasi Differential Revision: D37470292 Pulled By: gangliao fbshipit-source-id: fbca521b2791d3674dbf2484cea5fcae2fdd94d2	3 years ago
Gang Liao	ba1f62ddfb	Read from blob cache first when MultiGetBlob() (#10225) ... Summary: There is currently no caching mechanism for blobs, which is not ideal especially when the database resides on remote storage (where we cannot rely on the OS page cache). As part of this task, we would like to make it possible for the application to configure a blob cache. Pull Request resolved: https://github.com/facebook/rocksdb/pull/10225 Test Plan: Add test cases for MultiGetBlob In this task, we added the new API MultiGetBlob() for BlobSource. This PR is a part of https://github.com/facebook/rocksdb/issues/10156 Reviewed By: ltamasi Differential Revision: D37358364 Pulled By: gangliao fbshipit-source-id: aff053a37615d96d768fb9aedde17da5618c7ae6	3 years ago
Gang Liao	deff48bcef	Add blob source to retrieve blobs in RocksDB (#10198) ... Summary: There is currently no caching mechanism for blobs, which is not ideal especially when the database resides on remote storage (where we cannot rely on the OS page cache). As part of this task, we would like to make it possible for the application to configure a blob cache. In this task, we formally introduced the blob source to RocksDB. BlobSource is a new abstraction layer that provides universal access to blobs, regardless of whether they are in the blob cache, secondary cache, or (remote) storage. Depending on user settings, it always fetch blobs from multi-tier cache and storage with minimal cost. Note: The new `MultiGetBlob()` implementation is not included in the current PR. To go faster, we aim to create a separate PR for it in parallel! This PR is a part of https://github.com/facebook/rocksdb/issues/10156 Pull Request resolved: https://github.com/facebook/rocksdb/pull/10198 Reviewed By: ltamasi Differential Revision: D37294735 Pulled By: gangliao fbshipit-source-id: 9cb50422d9dd1bc03798501c2778b6c7520c7a1e	3 years ago
Peter Dillinger	501543573a	Fix bad include (#10213) ... Summary: include "include/rocksdb/blah.h" is messing up some internal builds vs. include "rocksdb/blah." This fixes the bad case and adds a check for future instances. Pull Request resolved: https://github.com/facebook/rocksdb/pull/10213 Test Plan: back-port to 7.4 release candidate and watch internal build Reviewed By: hx235 Differential Revision: D37296202 Pulled By: pdillinger fbshipit-source-id: d7cc6b2c57d858dff0444f19320d83c8b4f9b185	3 years ago
Gang Liao	c965c9ef65	Read blob from blob cache if exists when GetBlob() (#10178) ... Summary: There is currently no caching mechanism for blobs, which is not ideal especially when the database resides on remote storage (where we cannot rely on the OS page cache). As part of this task, we would like to make it possible for the application to configure a blob cache. In this task, we added a new abstraction layer `BlobSource` to retrieve blobs from either blob cache or raw blob file. Note: For simplicity, the current PR only includes `GetBlob()`. `MultiGetBlob()` will be included in the next PR. This PR is a part of https://github.com/facebook/rocksdb/issues/10156 Pull Request resolved: https://github.com/facebook/rocksdb/pull/10178 Reviewed By: ltamasi Differential Revision: D37250507 Pulled By: gangliao fbshipit-source-id: 3fc4a55a0cea955a3147bdc7dba06430e377259b	3 years ago