Summary:
Use a customzied BlockBasedTableIterator and LevelIterator to replace current implementations leveraging two-level-iterator. Hope the customized logic will make code easier to understand. As a side effect, BlockBasedTableIterator reduces the allocation for the data block iterator object, and avoid the virtual function call to it, because we can directly reference BlockIter, a final class. Similarly, LevelIterator reduces virtual function call to the dummy iterator iterating the file metadata. It also enabled further optimization.
The upper bound check is also moved from index block to data block. This implementation fits this iterator better. After the change, forwared iterator is slightly optimized to ensure we trim those iterators.
The two-level-iterator now is only used by partitioned index, so it is simplified.
Closes https://github.com/facebook/rocksdb/pull/3406
Differential Revision: D6809041
Pulled By: siying
fbshipit-source-id: 7da3b9b1d3c8e9d9405302c15920af1fcaf50ffa
Summary:
`ReadBlockFromFile` uses a stack buffer to hold small data blocks before passing them to the compression library, which outputs uncompressed data in a heap buffer. In the case of `kNoCompression` there is a `memcpy` to copy from stack buffer to heap buffer.
This PR optimizes `ReadBlockFromFile` to skip the stack buffer for files whose blocks are known to be uncompressed. We determine this using the SST file property, "compression_name", if it's available.
Closes https://github.com/facebook/rocksdb/pull/3472
Differential Revision: D6920848
Pulled By: ajkr
fbshipit-source-id: 5c753e804efc178b9229ae5dbe6a4adc32031f07
Summary:
RandomizedHarnessTest enumerates different combinations of test type, compression type, restart interval, etc. For some combinations it takes very long to finish, causing the test to time out in test infrastructure.
This PR split the test input into smaller trunks in the hope that they will fit in the timeout window. Another possibility is to reduce `num_entries` of course
Closes https://github.com/facebook/rocksdb/pull/3467
Differential Revision: D6910235
Pulled By: miasantreble
fbshipit-source-id: 717246ee5d21a8a48ad82d4d9c04f9051a66f07f
Summary:
Previously `ReadBlockFromFile` for data blocks was only measured when reading a block to populate block cache. This PR adds the corresponding measurements for users who disabled block cache.
Closes https://github.com/facebook/rocksdb/pull/3442
Differential Revision: D6848671
Pulled By: ajkr
fbshipit-source-id: bb4bbe1797fa2cc1d9a5bad44891af2b55384b41
Summary:
ReadOptions.fill_cache is set in compaction inputs and can be set by users in their queries too. It tells RocksDB not to put a data block used to block cache.
The memory used by the data block is, however, not trackable by users.
To make the system more manageable, we can cost the block to block cache while using it, and then release it after using.
Closes https://github.com/facebook/rocksdb/pull/3333
Differential Revision: D6670230
Pulled By: miasantreble
fbshipit-source-id: ab848d3ed286bd081a13ee1903de357b56cbc308
Summary: Grandfather in super old lint issues to make a clean slate for moving forward that allows us to have stronger enforcement on new issues.
Reviewed By: yiwu-arbug
Differential Revision: D6821806
fbshipit-source-id: 22797d31ec58e9eb0255d3b66fedfcfcb0dc127c
Summary:
This change improves the performance of iterators doing long range scans (e.g. big/full table scans in MyRocks) by using readahead and prefetching additional data on each disk IO. This prefetching is automatically enabled on noticing more than 2 IOs for the same table file during iteration. The readahead size starts with 8KB and is exponentially increased on each additional sequential IO, up to a max of 256 KB. This helps in cutting down the number of IOs needed to complete the range scan.
Constraints:
- The prefetched data is stored by the OS in page cache. So this currently works only for non direct-reads use-cases i.e applications which use page cache. (Direct-I/O support will be enabled in a later PR).
- This gets currently enabled only when ReadOptions.readahead_size = 0 (which is the default value).
Thanks to siying for the original idea and implementation.
**Benchmarks:**
Data fill:
```
TEST_TMPDIR=/data/users/$USER/benchmarks/iter ./db_bench -benchmarks=fillrandom -num=1000000000 -compression_type="none" -level_compaction_dynamic_level_bytes
```
Do a long range scan: Seekrandom with large number of nexts
```
TEST_TMPDIR=/data/users/$USER/benchmarks/iter ./db_bench -benchmarks=seekrandom -duration=60 -num=1000000000 -use_existing_db -seek_nexts=10000 -statistics -histogram
```
Page cache was cleared before each experiment with the command:
```
sudo sh -c "echo 3 > /proc/sys/vm/drop_caches"
```
```
Before:
seekrandom : 34020.945 micros/op 29 ops/sec; 32.5 MB/s (1636 of 1999 found)
With this change:
seekrandom : 8726.912 micros/op 114 ops/sec; 126.8 MB/s (5702 of 6999 found)
```
~3.9X performance improvement.
Also verified with strace and gdb that the readahead size is increasing as expected.
```
strace -e readahead -f -T -t -p <db_bench process pid>
```
Closes https://github.com/facebook/rocksdb/pull/3282
Differential Revision: D6586477
Pulled By: sagar0
fbshipit-source-id: 8a118a0ed4594fbb7f5b1cafb242d7a4033cb58c
Summary:
This is a pre-cleaning up before a major block based table iterator refactoring. BlockBasedTable::NewDataBlockIterator() will always return BlockIter. This simplifies the logic and code and enable further refactoring and optimization.
Closes https://github.com/facebook/rocksdb/pull/3398
Differential Revision: D6780165
Pulled By: siying
fbshipit-source-id: 273f7dc896724f682c0118fb69a359d9cc4418b4
Summary:
* Fix DBTest.CompactRangeWithEmptyBottomLevel lite build failure
* Fix DBTest.AutomaticConflictsWithManualCompaction failure introduce by #3366
* Fix BlockBasedTableTest::IndexUncompressed should be disabled if snappy is disabled
* Fix ASAN failure with DBBasicTest::DBClose test
Closes https://github.com/facebook/rocksdb/pull/3373
Differential Revision: D6732313
Pulled By: yiwu-arbug
fbshipit-source-id: 1eb9b9d9a8d795f56188fa9770db9353f6fdedc5
Summary:
Re-use metadata for reading Compression Dictionary on BlockBased
table open, this saves two reads from disk.
This helps to our 999 percentile in 5.6.1 where prefetch buffer is not present.
Closes https://github.com/facebook/rocksdb/pull/3354
Differential Revision: D6695753
Pulled By: ajkr
fbshipit-source-id: bb8acd9e9e66e65b89c548ab8940570ae360333c
Summary:
BlockTest.BlockReadAmpBitmap is too slow and times out in some environments. Speed it up by:
(1) improve the way the verification is done. With this it is 5 times faster
(2) run fewer tests for large blocks. This cut it down by another 10 times.
Now it can finish in similar time as other tests.
Closes https://github.com/facebook/rocksdb/pull/3313
Differential Revision: D6643711
Pulled By: siying
fbshipit-source-id: c2397d666eab5421a78ca87e1e45491e0f832a6d
Summary:
NUMBER_BLOCK_DECOMPRESSED and NUMBER_BLOCK_COMPRESSED are not reported unless the stats level contain detailed timers, which is wrong. They are normal counters. Fix it.
Closes https://github.com/facebook/rocksdb/pull/3263
Differential Revision: D6552519
Pulled By: siying
fbshipit-source-id: 40899ccea7b2856bb39752616657c0bfd432f6f9
Summary:
Some call sites of BlockFetcher create temporary ReadOptions and pass to BlockFetcher. The temporary object will be gone after BlockFetcher construction but BlockFetcher keep its reference, causing stack-use-after-scope. Fixing it.
Closes https://github.com/facebook/rocksdb/pull/3258
Differential Revision: D6547152
Pulled By: yiwu-arbug
fbshipit-source-id: 6b49e9dd46bb72307f5d8f88ea15faacff35b9bc
Summary:
Divide ReadBlockContents() to multiple sub-functions. Maintaining the input and intermediate data in a new class BlockFetcher.
I hope in general it makes the code easier to maintain.
Another motivation to do it is to clearly divide the logic before file reading and after file reading. The refactor will help us evaluate how can we make I/O async in the future.
Closes https://github.com/facebook/rocksdb/pull/3244
Differential Revision: D6520983
Pulled By: siying
fbshipit-source-id: 338d90bc0338472d46be7a7682028dc9114b12e9
Summary:
table/block.cc:
420 }
CID 1396127 (#1 of 1): Uninitialized scalar field (UNINIT_CTOR)
7. uninit_member: Non-static class member restart_offset_ is not initialized in this constructor nor in any functions that it calls.
421}
table/block_based_table_builder.cc:
CID 1418259 (#1 of 1): Uninitialized scalar field (UNINIT_CTOR)
7. uninit_member: Non-static class member compressed_cache_key_prefix_size is not initialized in this constructor nor in any functions that it calls.
table/block_based_table_reader.h:
3. uninit_member: Non-static class member index_type is not initialized in this constructor nor in any functions that it calls.
CID 1396147 (#1 of 1): Uninitialized scalar field (UNINIT_CTOR)
5. uninit_member: Non-static class member hash_index_allow_collision is not initialized in this constructor nor in any functions that it calls.
413 global_seqno(kDisableGlobalSequenceNumber) {}
414
table/cuckoo_table_reader.cc:
55 if (hash_funs == user_props.end()) {
56 status_ = Status::Corruption("Number of hash functions not found");
5. uninit_member: Non-static class member is_last_level_ is not initialized in this constructor nor in any functions that it calls.
7. uninit_member: Non-static class member identity_as_first_hash_ is not initialized in this constructor nor in any functions that it calls.
9. uninit_member: Non-static class member use_module_hash_ is not initialized in this constructor nor in any functions that it calls.
11. uninit_member: Non-static class member num_hash_func_ is not initialized in this constructor nor in any functions that it calls.
13. uninit_member: Non-static class member key_length_ is not initialized in this constructor nor in any functions that it calls.
15. uninit_member: Non-static class member user_key_length_ is not initialized in this constructor nor in any functions that it calls.
17. uninit_member: Non-static class member value_length_ is not initialized in this constructor nor in any functions that it calls.
19. uninit_member: Non-static class member bucket_length_ is not initialized in this constructor nor in any functions that it calls.
21. uninit_member: Non-static class member cuckoo_block_size_ is not initialized in this constructor nor in any functions that it calls.
23. uninit_member: Non-static class member cuckoo_block_bytes_minus_one_ is not initialized in this constructor nor in any functions that it calls.
CID 1322785 (#2 of 2): Uninitialized scalar field (UNINIT_CTOR)
25. uninit_member: Non-static class member table_size_ is not initialized in this constructor nor in any functions that it calls.
57 return;
table/plain_table_index.h:
2. uninit_member: Non-static class member index_size_ is not initialized in this constructor nor in any functions that it calls.
CID 1322801 (#1 of 1): Uninitialized scalar field (UNINIT_CTOR)
4. uninit_member: Non-static class member sub_index_size_ is not initialized in this constructor nor in any functions that it calls.
128 huge_page_tlb_size_(huge_page_tlb_size) {}
129
Closes https://github.com/facebook/rocksdb/pull/3113
Differential Revision: D6505719
Pulled By: yiwu-arbug
fbshipit-source-id: 38f44d8f9dfefb4c2e25d83b8df25a5201c75618
Summary:
I started adding gflags support for cmake on linux and got frustrated that I'd need to duplicate the build_detect_platform logic, which determines namespace based on attempting compilation. We can do it differently -- use the GFLAGS_NAMESPACE macro if available, and if not, that indicates it's an old gflags version without configurable namespace so we can simply hardcode "google".
Closes https://github.com/facebook/rocksdb/pull/3212
Differential Revision: D6456973
Pulled By: ajkr
fbshipit-source-id: 3e6d5bde3ca00d4496a120a7caf4687399f5d656
Summary:
The ASCII output is almost always useless to me as the first '\0' byte in the key or value causes it to stop printing. Since all characters are already surrounded by spaces, "\ 0" (how we display a backslash followed by a zero) and "\0" (how this PR displays a null terminator) are distinguishable. My assumption is the value of seeing all the bytes outweighs the value of the alignment we had before, where we always had one character followed by one space.
Closes https://github.com/facebook/rocksdb/pull/3203
Differential Revision: D6428651
Pulled By: ajkr
fbshipit-source-id: aafc978a51e9ea029cfe3e763e2bb0e1751b9ccf
Summary:
Problem: Option string accepts only cache_size as parameter for block_cache which is specified as "block_cache=1M".
It doesn't accept other parameters like num_shards etc.
Changes :
1) ParseBlockBasedTableOption in block_based_table_factory is edited to accept cache options in the format "block_cache=<cache_size>:<num_shard_bits>:<strict_capacity_limit>:<high_pri_pool_ratio>".
Options other than cache_size are optional to maintain backward compatibility. The changes are valid for block_cache_compressed as well.
For example, "block_cache=1M:6:true:0.5", "block_cache=1M:6:true", "block_cache=1M:6" and "block_cache=1M" are all valid option strings.
2) Corresponding unit tests are added.
Closes https://github.com/facebook/rocksdb/pull/3108
Differential Revision: D6420997
Pulled By: sagar0
fbshipit-source-id: cdea8b785688d2802907974af27225ccc1c0cd43
Summary:
block_size_deviation is in percentage while the partition size is in bytes. The current code fails to take that into account resulting into very large target size for filter partitions.
Closes https://github.com/facebook/rocksdb/pull/3187
Differential Revision: D6376069
Pulled By: maysamyabandeh
fbshipit-source-id: 276546fc68f50e0da32c462abb46f6cf676db9b2
Summary:
We don't propagate TableProperty::oldest_key_time on compaction and just write the default value to SST files. It is more natural to default the value to 0.
Also revert db_sst_test back to before #2842.
Closes https://github.com/facebook/rocksdb/pull/3079
Differential Revision: D6165702
Pulled By: yiwu-arbug
fbshipit-source-id: ca3ce5928d96ae79a5beb12bb7d8c640a71478a0
Summary:
With FIFO compaction we would like to get the oldest data time for monitoring. The problem is we don't have timestamp for each key in the DB. As an approximation, we expose the earliest of sst file "creation_time" property.
My plan is to override the property with a more accurate value with blob db, where we actually have timestamp.
Closes https://github.com/facebook/rocksdb/pull/2842
Differential Revision: D5770600
Pulled By: yiwu-arbug
fbshipit-source-id: 03833c8f10bbfbee62f8ea5c0d03c0cafb5d853a
Summary:
Currently, RocksDB does not allow reopening a preexisting DB with no merge operator defined, with a merge operator defined. This means that if a DB ever want to add a merge operator, there's no way to do so currently.
Fix this by adding a new verification type `kByNameAllowFromNull` which will allow old values to be nullptr, and new values to be non-nullptr.
Closes https://github.com/facebook/rocksdb/pull/2958
Differential Revision: D5961131
Pulled By: lth
fbshipit-source-id: 06179bebd0d90db3d43690b5eb7345e2d5bab1eb
Summary:
Add kTypeBlobIndex value type, which will be used by blob db only, to insert a (key, blob_offset) KV pair. The purpose is to
1. Make it possible to open existing rocksdb instance as blob db. Existing value will be of kTypeIndex type, while value inserted by blob db will be of kTypeBlobIndex.
2. Make rocksdb able to detect if the db contains value written by blob db, if so return error.
3. Make it possible to have blob db optionally store value in SST file (with kTypeValue type) or as a blob value (with kTypeBlobIndex type).
The root db (DBImpl) basically pretended kTypeBlobIndex are normal value on write. On Get if is_blob is provided, return whether the value read is of kTypeBlobIndex type, or return Status::NotSupported() status if is_blob is not provided. On scan allow_blob flag is pass and if the flag is true, return wether the value is of kTypeBlobIndex type via iter->IsBlob().
Changes on blob db side will be in a separate patch.
Closes https://github.com/facebook/rocksdb/pull/2886
Differential Revision: D5838431
Pulled By: yiwu-arbug
fbshipit-source-id: 3c5306c62bc13bb11abc03422ec5cbcea1203cca
Summary:
In SST files, restart interval helps us search in data blocks. However, some meta blocks will be read sequentially, so there's no need for restart points. Restart interval will introduce extra space in the block (https://github.com/facebook/rocksdb/blob/master/table/block_builder.cc#L80). We will see if we can remove this redundant space. (Maybe set restart interval to infinite.)
Closes https://github.com/facebook/rocksdb/pull/2940
Differential Revision: D5930139
Pulled By: miasantreble
fbshipit-source-id: 92b1b23c15cffa90378343ac846b713623b19c21
Summary:
When using with compressed cache it is possible that the status is ok but the block is not actually added to the block cache. The patch takes this case into account.
Closes https://github.com/facebook/rocksdb/pull/2945
Differential Revision: D5937613
Pulled By: maysamyabandeh
fbshipit-source-id: 5428cf1115e5046b3d01ab78d26cb181122af4c6
Summary:
For every merge operand encountered for a key in the read path we now have the ability to decide whether to look further (to retrieve more merge operands for the key) or stop and invoke the merge operator to return the value. The user needs to override `ShouldMerge()` method with a condition to terminate search when true to avail this facility.
This has a couple of advantages:
1. It helps in limiting the number of merge operands that are looked at to compute a value as part of a user Get operation.
2. It allows to peek at a merge key-value to see if further merge operands need to look at.
Example: Limiting the number of merge operands that are looked at: Lets say you have 10 merge operands for a key spread over various levels. If you only want RocksDB to look at the latest two merge operands instead of all 10 to compute the value, it is now possible with this PR. You can set the condition in `ShouldMerge()` to return true when the size of the operand list is 2. Look at the example implementation in the unit test. Without this PR, a Get might look at all the 10 merge operands in different levels before invoking the merge-operator.
Added a new unit test.
Made sure that there is no perf regression by running benchmarks.
Command line to Load data:
```
TEST_TMPDIR=/dev/shm ./db_bench --benchmarks="mergerandom" --merge_operator="uint64add" --num=10000000
...
mergerandom : 12.861 micros/op 77757 ops/sec; 8.6 MB/s ( updates:10000000)
```
**ReadRandomMergeRandom bechmark results:**
Command line:
```
TEST_TMPDIR=/dev/shm ./db_bench --benchmarks="readrandommergerandom" --merge_operator="uint64add" --num=10000000
```
Base -- Without this code change (on commit fc7476b):
```
readrandommergerandom : 38.586 micros/op 25916 ops/sec; (reads:3001599 merges:6998401 total:10000000 hits:842235 maxlength:8)
```
With this code change:
```
readrandommergerandom : 38.653 micros/op 25870 ops/sec; (reads:3001599 merges:6998401 total:10000000 hits:842235 maxlength:8)
```
Closes https://github.com/facebook/rocksdb/pull/2923
Differential Revision: D5898239
Pulled By: sagar0
fbshipit-source-id: daefa325019f77968639a75c851d46352c2303ef
Summary:
A user encountered segfault on the call to `CacheDependencies()`, probably because `NewIndexIterator()` failed before populating `*index_entry`. Let's avoid the call in that case.
Closes https://github.com/facebook/rocksdb/pull/2939
Differential Revision: D5928611
Pulled By: ajkr
fbshipit-source-id: 484be453dbb00e5e160e9c6a1bc933df7d80f574
Summary:
Three small optimizations:
(1) iter_->IsKeyPinned() shouldn't be called if read_options.pin_data is not true. This may trigger function call all the way down the iterator tree.
(2) reuse the iterator key object in DBIter::FindNextUserEntryInternal(). The constructor of the class has some overheads.
(3) Move the switching direction logic in MergingIterator::Next() to a separate function.
These three in total improves readseq performance by about 3% in my benchmark setting.
Closes https://github.com/facebook/rocksdb/pull/2880
Differential Revision: D5829252
Pulled By: siying
fbshipit-source-id: 991aea10c6d6c3b43769cb4db168db62954ad1e3
Summary:
Merging iterator invokes InternalKeyComparator.Compare() frequently to heap merge. By making InternalKeyComparator final and merging iterator to directly use InternalKeyComparator rather than through Iterator interface, we can give compiler a choice to avoid one more virtual function call if possible. I ran readseq benchmark in memory-only use case to make sure the performance at least doesn't regress.
I have to disable the final key word in debug build, as a hack test class depends on overriding the class.
Closes https://github.com/facebook/rocksdb/pull/2860
Differential Revision: D5800461
Pulled By: siying
fbshipit-source-id: ab876f22a09bb5c560740911412336e0e25ccb53
Summary:
This patch instruments the read path to verify each read value against an optional ReadCallback class. If the value is rejected, the reader moves on to the next value. The WritePreparedTxn makes use of this feature to skip sequence numbers that are not in the read snapshot.
Closes https://github.com/facebook/rocksdb/pull/2850
Differential Revision: D5787375
Pulled By: maysamyabandeh
fbshipit-source-id: 49d808b3062ab35e7ae98ad388f659757794184c
Summary:
store a zero as the checksum when disabled since it's easier to keep block trailer a fixed length.
Closes https://github.com/facebook/rocksdb/pull/2781
Differential Revision: D5694702
Pulled By: ajkr
fbshipit-source-id: 69cea9da415778ba2b600dfd9d0dfc8cb5188ecd
Summary:
This is the warning that clang considers a bug and has been causing it to fail:
```
table/block_based_table_reader.cc:240:27: warning: Potential leak of memory pointed to by 'block.value'
for (; biter.Valid(); biter.Next()) {
^~~~~
```
Actually clang just doesn't have enough knowledge to statically determine it's safe. We can teach it using an assert.
Closes https://github.com/facebook/rocksdb/pull/2779
Differential Revision: D5691225
Pulled By: ajkr
fbshipit-source-id: 3f0d545bf44636953b30ee5243c63239e8f16d8e
Summary:
Allow `Slice` holding nullptr as a sentinel value but not in comparisons. This new restriction eliminates the need for the manual checks in 39ef900551, while still conforming to glibc's `memcmp` API. Thanks siying for the idea. Users may need to migrate, so mentioned it in HISTORY.md.
Closes https://github.com/facebook/rocksdb/pull/2777
Differential Revision: D5686016
Pulled By: ajkr
fbshipit-source-id: 03a2ca3fd9a0ebade9d0d5686c81d59a9534f563
Summary:
This is the continuation of https://github.com/facebook/rocksdb/pull/2661 for filter partitions. When pin_l0 is set (along with cache_xxx), then open table open the filter partitions are loaded into the cache and pinned there.
Closes https://github.com/facebook/rocksdb/pull/2766
Differential Revision: D5671098
Pulled By: maysamyabandeh
fbshipit-source-id: 174f24018f1d7f1129621e7380287b65b67d2115
Summary:
This fixes the existing logic for pinning l0 index partitions. The patch preloads the partitions into block cache and pin them if they belong to level 0 and pin_l0 is set.
The drawback is that it does many small IOs when preloading all the partitions into the cache is direct io is enabled. Working for a solution for that.
Closes https://github.com/facebook/rocksdb/pull/2661
Differential Revision: D5554010
Pulled By: maysamyabandeh
fbshipit-source-id: 1e6f32a3524d71355c77d4138516dcfb601ca7b2
Summary:
Right now, if direct I/O is enabled, prefetching the last 512KB cannot be applied, except compaction inputs or readahead is enabled for iterators. This can create a lot of I/O for HDD cases. To solve the problem, the 512KB is prefetched in block based table if direct I/O is enabled. The prefetched buffer is passed in totegher with random access file reader, so that we try to read from the buffer before reading from the file. This can be extended in the future to support flexible user iterator readahead too.
Closes https://github.com/facebook/rocksdb/pull/2708
Differential Revision: D5593091
Pulled By: siying
fbshipit-source-id: ee36ff6d8af11c312a2622272b21957a7b5c81e7
Summary:
We need a tool to check any sst file corruption in the db.
It will check all the sst files in current version and read all the blocks (data, meta, index) with checksum verification. If any verification fails, the function will return non-OK status.
Closes https://github.com/facebook/rocksdb/pull/2498
Differential Revision: D5324269
Pulled By: lightmark
fbshipit-source-id: 6f8a272008b722402a772acfc804524c9d1a483b
Summary:
Replace dynamic_cast<> so that users can choose to build with RTTI off, so that they can save several bytes per object, and get tiny more memory available.
Some nontrivial changes:
1. Add Comparator::GetRootComparator() to get around the internal comparator hack
2. Add the two experiemental functions to DB
3. Add TableFactory::GetOptionString() to avoid unnecessary casting to get the option string
4. Since 3 is done, move the parsing option functions for table factory to table factory files too, to be symmetric.
Closes https://github.com/facebook/rocksdb/pull/2645
Differential Revision: D5502723
Pulled By: siying
fbshipit-source-id: fd13cec5601cf68a554d87bfcf056f2ffa5fbf7c
Summary:
Breaking commit: d12691b86f
In the above commit, I moved the `TableCache` cleanup logic from `Version` destructor into `PurgeObsoleteFiles`. I missed cleaning up `TableCache` entries for the current `Version` during DB destruction.
This PR adds that logic to `VersionSet` destructor. One unfortunate side effect is now we're potentially deleting `TableReader`s after `column_family_set_.reset()`, which means we can't call `BlockBasedTableReader::Close` a second time as the block cache might already be destroyed.
Closes https://github.com/facebook/rocksdb/pull/2662
Differential Revision: D5515108
Pulled By: ajkr
fbshipit-source-id: 2cb820e19aa813e0d258d17f76b2d7b6b7ee0b18
