Summary:
Move WritePreparedTxnDB from pessimistic_transaction_db.h to its own header, write_prepared_txn_db.h
Closes https://github.com/facebook/rocksdb/pull/3114
Differential Revision: D6220987
Pulled By: maysamyabandeh
fbshipit-source-id: 18893fb4fdc6b809fe117dabb544080f9b4a301b
Summary:
It's also defined in db/dbformat.cc per 7fe3b32896
Closes https://github.com/facebook/rocksdb/pull/3111
Differential Revision: D6219140
Pulled By: ajkr
fbshipit-source-id: 0f2b14e41457334a4665c6b7e3f42f1a060a0f35
Summary:
Implements ValidateSnapshot for WritePrepared txns and also adds a unit test to clarify the contract of this function.
Closes https://github.com/facebook/rocksdb/pull/3101
Differential Revision: D6199405
Pulled By: maysamyabandeh
fbshipit-source-id: ace509934c307ea5d26f4bbac5f836d7c80fd240
Summary:
The motivation for this PR is to add to RocksDB support for differential (incremental) snapshots, as snapshot of the DB changes between two points in time (one can think of it as diff between to sequence numbers, or the diff D which can be thought of as an SST file or just set of KVs that can be applied to sequence number S1 to get the database to the state at sequence number S2).
This feature would be useful for various distributed storages layers built on top of RocksDB, as it should help reduce resources (time and network bandwidth) needed to recover and rebuilt DB instances as replicas in the context of distributed storages.
From the API standpoint that would like client app requesting iterator between (start seqnum) and current DB state, and reading the "diff".
This is a very draft PR for initial review in the discussion on the approach, i'm going to rework some parts and keep updating the PR.
For now, what's done here according to initial discussions:
Preserving deletes:
- We want to be able to optionally preserve recent deletes for some defined period of time, so that if a delete came in recently and might need to be included in the next incremental snapshot it would't get dropped by a compaction. This is done by adding new param to Options (preserve deletes flag) and new variable to DB Impl where we keep track of the sequence number after which we don't want to drop tombstones, even if they are otherwise eligible for deletion.
- I also added a new API call for clients to be able to advance this cutoff seqnum after which we drop deletes; i assume it's more flexible to let clients control this, since otherwise we'd need to keep some kind of timestamp < -- > seqnum mapping inside the DB, which sounds messy and painful to support. Clients could make use of it by periodically calling GetLatestSequenceNumber(), noting the timestamp, doing some calculation and figuring out by how much we need to advance the cutoff seqnum.
- Compaction codepath in compaction_iterator.cc has been modified to avoid dropping tombstones with seqnum > cutoff seqnum.
Iterator changes:
- couple params added to ReadOptions, to optionally allow client to request internal keys instead of user keys (so that client can get the latest value of a key, be it delete marker or a put), as well as min timestamp and min seqnum.
TableCache changes:
- I modified table_cache code to be able to quickly exclude SST files from iterators heep if creation_time on the file is less then iter_start_ts as passed in ReadOptions. That would help a lot in some DB settings (like reading very recent data only or using FIFO compactions), but not so much for universal compaction with more or less long iterator time span.
What's left:
- Still looking at how to best plug that inside DBIter codepath. So far it seems that FindNextUserKeyInternal only parses values as UserKeys, and iter->key() call generally returns user key. Can we add new API to DBIter as internal_key(), and modify this internal method to optionally set saved_key_ to point to the full internal key? I don't need to store actual seqnum there, but I do need to store type.
Closes https://github.com/facebook/rocksdb/pull/2999
Differential Revision: D6175602
Pulled By: mikhail-antonov
fbshipit-source-id: c779a6696ee2d574d86c69cec866a3ae095aa900
Summary:
GetCommitTimeWriteBatch is currently used to store some state as part of commit in 2PC. In MyRocks it is specifically used to store some data that would be needed only during recovery. So it is not need to be stored in memtable right after each commit.
This patch enables an optimization to write the GetCommitTimeWriteBatch only to the WAL. The batch will be written to memtable during recovery when the WAL is replayed. To cover the case when WAL is deleted after memtable flush, the batch is also buffered and written to memtable right before each memtable flush.
Closes https://github.com/facebook/rocksdb/pull/3071
Differential Revision: D6148023
Pulled By: maysamyabandeh
fbshipit-source-id: 2d09bae5565abe2017c0327421010d5c0d55eaa7
Summary:
The collapse of duplicate keys in write batch needs to sort the indexes of duplicate keys since it only checks the index in the batch with the head of the list of duplicate keys.
Closes https://github.com/facebook/rocksdb/pull/3093
Differential Revision: D6186800
Pulled By: maysamyabandeh
fbshipit-source-id: abc9ae8c2f1840445a5584f925cf86ecc6f37154
Summary:
* cleanup num_concurrent_simple_blobs. We don't do concurrent writes (by taking write_mutex_) so it doesn't make sense to have multiple non TTL files open. We can revisit later when we want to improve writes.
* cleanup eviction callback. we don't have plan to use it now.
* rename s/open_simple_blob_files_/open_non_ttl_file_/ and s/open_blob_files_/open_ttl_files_/ to avoid confusion.
Closes https://github.com/facebook/rocksdb/pull/3088
Differential Revision: D6182598
Pulled By: yiwu-arbug
fbshipit-source-id: 99e6f5e01fa66d31309cdb06ce48502464bac6ad
Summary:
There seems to be a typo mistake in env ReuseWritableFile func
where status is being returned twice.
Closes https://github.com/facebook/rocksdb/pull/3099
Differential Revision: D6196204
Pulled By: ajkr
fbshipit-source-id: abb6e3e1c1e772dd485fc39e7f1b9d502fa188fe
Summary:
- Release all snapshots before crashing and reopening the DB. Without this, we may attempt to release snapshots from an old DB using a new DB. That tripped an assertion.
- Release multiple snapshots in the same operation if needed. Without this, we would sometimes leak snapshots.
Closes https://github.com/facebook/rocksdb/pull/3098
Differential Revision: D6194923
Pulled By: ajkr
fbshipit-source-id: b9c89bcca7ebcbb6c7802c616f9d1175a005aadf
Summary:
The assertion was caught by `MySQLStyleTransactionTest/MySQLStyleTransactionTest.TransactionStressTest/5` when run in a loop. The caller doesn't track whether the released snapshot is oldest, so let this function handle that case.
Closes https://github.com/facebook/rocksdb/pull/3080
Differential Revision: D6185257
Pulled By: ajkr
fbshipit-source-id: 4b3015c11db5d31e46521a00af568546ef4558cd
Summary:
write_options.sync = true and write_options.disableWAL is incompatible. When WAL is disabled, we are not able to persist the write immediately. Return an error in this case to avoid misuse of the options.
Closes https://github.com/facebook/rocksdb/pull/3086
Differential Revision: D6176822
Pulled By: yiwu-arbug
fbshipit-source-id: 1eb10028c14fe7d7c13c8bc12c0ef659f75aa071
Summary:
Problem was in bottommost compaction, when an L0->L0 compaction happened and L0 was bottommost. Then we'd preserve tombstones according to `Compaction::KeyNotExistsBeyondOutputLevel`, while zeroing seqnum according to `CompactionIterator::PrepareOutput`, thus triggering the assertion in `PrepareOutput`. To fix, we can just drop tombstones in L0->L0 when the output is "bottommost", i.e., the compaction includes the oldest L0 file and there's nothing at lower levels.
Closes https://github.com/facebook/rocksdb/pull/3085
Differential Revision: D6175742
Pulled By: ajkr
fbshipit-source-id: 8ab19a2e001496f362e9eb0a71757e2f6ecfdb3b
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:
SstFileManager move files that need to be deleted into a trash directory.
Deprecate this behaviour and instead add ".trash" extension to files that need to be deleted
Closes https://github.com/facebook/rocksdb/pull/2970
Differential Revision: D5976805
Pulled By: IslamAbdelRahman
fbshipit-source-id: 27374ece4315610b2792c30ffcd50232d4c9a343
Summary:
Changing blob file format and some code cleanup around the change. The change with blob log format are:
* Remove timestamp field in blob file header, blob file footer and blob records. The field is not being use and often confuse with expiration field.
* Blob file header now come with column family id, which always equal to default column family id. It leaves room for future support of column family.
* Compression field in blob file header now is a standalone byte (instead of compact encode with flags field)
* Blob file footer now come with its own crc.
* Key length now being uint64_t instead of uint32_t
* Blob CRC now checksum both key and value (instead of value only).
* Some reordering of the fields.
The list of cleanups:
* Better inline comments in blob_log_format.h
* rename ttlrange_t and snrange_t to ExpirationRange and SequenceRange respectively.
* simplify blob_db::Reader
* Move crc checking logic to inside blob_log_format.cc
Closes https://github.com/facebook/rocksdb/pull/3081
Differential Revision: D6171304
Pulled By: yiwu-arbug
fbshipit-source-id: e4373e0d39264441b7e2fbd0caba93ddd99ea2af
Summary:
db/column_family.h :
79 ColumnFamilyHandleInternal()
CID 1322806 (#1 of 1): Uninitialized pointer field (UNINIT_CTOR)
2. uninit_member: Non-static class member internal_cfd_ is not initialized in this constructor nor in any functions that it calls.
80 : ColumnFamilyHandleImpl(nullptr, nullptr, nullptr) {}
db/compacted_db_impl.cc:
18CompactedDBImpl::CompactedDBImpl(
19 const DBOptions& options, const std::string& dbname)
20 : DBImpl(options, dbname) {
2. uninit_member: Non-static class member cfd_ is not initialized in this constructor nor in any functions that it calls.
4. uninit_member: Non-static class member version_ is not initialized in this constructor nor in any functions that it calls.
CID 1396120 (#1 of 1): Uninitialized pointer field (UNINIT_CTOR)
6. uninit_member: Non-static class member user_comparator_ is not initialized in this constructor nor in any functions that it calls.
21}
db/compaction_iterator.cc:
9. uninit_member: Non-static class member current_user_key_sequence_ is not initialized in this constructor nor in any functions that it calls.
11. uninit_member: Non-static class member current_user_key_snapshot_ is not initialized in this constructor nor in any functions that it calls.
CID 1419855 (#1 of 1): Uninitialized scalar field (UNINIT_CTOR)
13. uninit_member: Non-static class member current_key_committed_ is not initialized in this constructor nor in any functions that it calls.
Closes https://github.com/facebook/rocksdb/pull/3084
Differential Revision: D6172999
Pulled By: sagar0
fbshipit-source-id: 084d73393faf8022c01359cfb445807b6a782460
Summary:
228MutableDBOptions::MutableDBOptions()
229 : max_background_jobs(2),
230 base_background_compactions(-1),
231 max_background_compactions(-1),
232 avoid_flush_during_shutdown(false),
233 delayed_write_rate(2 * 1024U * 1024U),
234 max_total_wal_size(0),
235 delete_obsolete_files_period_micros(6ULL * 60 * 60 * 1000000),
236 stats_dump_period_sec(600),
2. uninit_member: Non-static class member bytes_per_sync is not initialized in this constructor nor in any functions that it calls.
CID 1419857 (#1 of 1): Uninitialized scalar field (UNINIT_CTOR)
4. uninit_member: Non-static class member wal_bytes_per_sync is not initialized in this constructor nor in any functions that it calls.
237 max_open_files(-1) {}
Closes https://github.com/facebook/rocksdb/pull/3069
Differential Revision: D6170424
Pulled By: ajkr
fbshipit-source-id: 1f94e86b87611ad2330b8b1707911150978d68b8
Summary:
- for `SeekToFirst()`, just convert it to a regular `Seek()` if lower bound is specified
- for operations that iterate backwards over user keys (`SeekForPrev`, `SeekToLast`, `Prev`), change `PrevInternal` to check whether user key went below lower bound every time the user key changes -- same approach we use to ensure we stay within a prefix when `prefix_same_as_start=true`.
Closes https://github.com/facebook/rocksdb/pull/3074
Differential Revision: D6158654
Pulled By: ajkr
fbshipit-source-id: cb0e3a922e2650d2cd4d1c6e1c0f1e8b729ff518
Summary:
Adding the `min_blob_size` option to allow storing small values in base db (in LSM tree) together with the key. The goal is to improve performance for small values, while taking advantage of blob db's low write amplification for large values.
Also adding expiration timestamp to blob index. It will be useful to evict stale blob indexes in base db by adding a compaction filter. I'll work on the compaction filter in future patches.
See blob_index.h for the new blob index format. There are 4 cases when writing a new key:
* small value w/o TTL: put in base db as normal value (i.e. ValueType::kTypeValue)
* small value w/ TTL: put (type, expiration, value) to base db.
* large value w/o TTL: write value to blob log and put (type, file, offset, size, compression) to base db.
* large value w/TTL: write value to blob log and put (type, expiration, file, offset, size, compression) to base db.
Closes https://github.com/facebook/rocksdb/pull/3066
Differential Revision: D6142115
Pulled By: yiwu-arbug
fbshipit-source-id: 9526e76e19f0839310a3f5f2a43772a4ad182cd0
Summary:
When snapshots are held for a long time, files may reach the bottom level containing overwritten/deleted keys. We previously had no mechanism to trigger compaction on such files. This particularly impacted DBs that write to different parts of the keyspace over time, as such files would never be naturally compacted due to second-last level files moving down. This PR introduces a mechanism for bottommost files to be recompacted upon releasing all snapshots that prevent them from dropping their deleted/overwritten keys.
- Changed `CompactionPicker` to compact files in `BottommostFilesMarkedForCompaction()`. These are the last choice when picking. Each file will be compacted alone and output to the same level in which it originated. The goal of this type of compaction is to rewrite the data excluding deleted/overwritten keys.
- Changed `ReleaseSnapshot()` to recompute the bottom files marked for compaction when the oldest existing snapshot changes, and schedule a compaction if needed. We cache the value that oldest existing snapshot needs to exceed in order for another file to be marked in `bottommost_files_mark_threshold_`, which allows us to avoid recomputing marked files for most snapshot releases.
- Changed `VersionStorageInfo` to track the list of bottommost files, which is recomputed every time the version changes by `UpdateBottommostFiles()`. The list of marked bottommost files is first computed in `ComputeBottommostFilesMarkedForCompaction()` when the version changes, but may also be recomputed when `ReleaseSnapshot()` is called.
- Extracted core logic of `Compaction::IsBottommostLevel()` into `VersionStorageInfo::RangeMightExistAfterSortedRun()` since logic to check whether a file is bottommost is now necessary outside of compaction.
Closes https://github.com/facebook/rocksdb/pull/3009
Differential Revision: D6062044
Pulled By: ajkr
fbshipit-source-id: 123d201cf140715a7d5928e8b3cb4f9cd9f7ad21
Summary:
I found that we continue accepting writes even when the blob db goes beyond the configured blob directory size limit. Now, we return an error for writes on reaching `blob_dir_size` limit and if `is_fifo` is set to false. (We cannot just drop any file when `is_fifo` is true.)
Deleting the oldest file when `is_fifo` is true will be handled in a later PR.
Closes https://github.com/facebook/rocksdb/pull/3060
Differential Revision: D6136156
Pulled By: sagar0
fbshipit-source-id: 2f11cb3f2eedfa94524fbfa2613dd64bfad7a23c
Summary:
When doing a Seek() or SeekForPrev() we should stop the moment we see a key with a different prefix as start if ReadOptions:: prefix_same_as_start was set to true
Right now we don't stop if we encounter a tombstone outside the prefix while executing SeekForPrev()
Closes https://github.com/facebook/rocksdb/pull/3067
Differential Revision: D6149638
Pulled By: IslamAbdelRahman
fbshipit-source-id: 7f659862d2bf552d3c9104a360c79439ceba2f18
Summary:
A few simple changes to allow RocksDB to be built on OpenBSD. Let me know if any further changes are needed.
Closes https://github.com/facebook/rocksdb/pull/3061
Differential Revision: D6138800
Pulled By: ajkr
fbshipit-source-id: a13a17b5dc051e6518bd56a8c5efd1d24dd81b0c
Summary:
Java's `Status.SubCode` was out of sync with `include/rocksdb/status.h:SubCode`.
When running out of disc space this led to an `IllegalArgumentException` because of an invalid status code, rather than just returning the corresponding status code without an exception.
I added the missing status codes.
By this, we keep the behaviour of throwing an `IllegalArgumentException` in case of newly added status codes that are defined in C but not in Java.
We could think of an alternative strategy: add in Java another code "UnknownCode" which acts as a catch-all for all those status codes that are not yet mirrored from C to Java. This approach would never throw an exception but simply return a non-OK status-code.
I think the current approach of throwing an Exception in case of a C/Java inconsistency is fine, but if you have some opinion on the alternative strategy, then feel free to comment here.
Closes https://github.com/facebook/rocksdb/pull/3050
Differential Revision: D6129682
Pulled By: sagar0
fbshipit-source-id: f2bf44caad650837cffdcb1f93eb793b43580c66
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:
MSVC does not support unused attribute at this time. A separate assignment line fixes the issue probably by being counted as usage for MSVC and it no longer complains about unused var.
Closes https://github.com/facebook/rocksdb/pull/3048
Differential Revision: D6126272
Pulled By: maysamyabandeh
fbshipit-source-id: 4907865db45fd75a39a15725c0695aaa17509c1f
Summary:
Enable concurrent_prepare flag for WritePrepared transactions and extend the existing transaction tests with this config.
Closes https://github.com/facebook/rocksdb/pull/3046
Differential Revision: D6106534
Pulled By: maysamyabandeh
fbshipit-source-id: 88c8d21d45bc492beb0a131caea84a2ac5e7d38c
Summary:
This test shouldn't be enabled under the lite version; and this fixes the failing contrun test due to #3006.
Closes https://github.com/facebook/rocksdb/pull/3056
Differential Revision: D6114681
Pulled By: sagar0
fbshipit-source-id: dc5243549ae6b1353cec7edb820c771d95f66dda
Summary:
The test currently times out when it is run under tsan. This patch split it into 4 tests.
Closes https://github.com/facebook/rocksdb/pull/3047
Differential Revision: D6106515
Pulled By: maysamyabandeh
fbshipit-source-id: 03a28cdf8b1c097be2361b1b0cc3dc1acf2b5d63
Summary:
Add options to `db_stress` (correctness testing tool) to randomly acquire snapshot and release it after some period of time. It's useful for correctness testing of #3009, as well as other parts of compaction that behave differently depending on which snapshots are held.
Closes https://github.com/facebook/rocksdb/pull/3038
Differential Revision: D6086501
Pulled By: ajkr
fbshipit-source-id: 3ec0d8666c78ac507f1f808887c4ff759ba9b865
Summary:
fixup 6a541afcc4. This code didn't do anything because (1) `bytes_per_sync` is assigned in `EnvOptions`'s constructor; and (2) `OptimizeForCompactionTableWrite`'s return value was ignored, even though its only purpose is to return something.
Closes https://github.com/facebook/rocksdb/pull/3055
Differential Revision: D6114132
Pulled By: ajkr
fbshipit-source-id: ea4831770930e9cf83518e13eb2e1934d1f5487c
Summary:
Fix unstable floating point exception, tested on Windows, 64-bit build.
The problem appeared in `SetCapacity()` method at line
`high_pri_pool_capacity_ = capacity_ * high_pri_pool_ratio_;`
`high_pri_pool_ratio_` was not initialized at that moment, because
`SetHighPriorityPoolRatio()` is called after `SetCapacity()`. So,
`high_pri_pool_ratio_` contained garbage, which caused "Floating point
exception" sometimes.
Closes https://github.com/facebook/rocksdb/pull/3052
Differential Revision: D6111161
Pulled By: yiwu-arbug
fbshipit-source-id: d170329111ad12b4bf9bbcf37bcb6411523438ae
Summary:
ColumnFamilyOptions::compaction_options_fifo and all its sub-fields can be set dynamically now.
Some of the ways in which the fifo compaction options can be set are:
- `SetOptions({{"compaction_options_fifo", "{max_table_files_size=1024}"}})`
- `SetOptions({{"compaction_options_fifo", "{ttl=600;}"}})`
- `SetOptions({{"compaction_options_fifo", "{max_table_files_size=1024;ttl=600;}"}})`
- `SetOptions({{"compaction_options_fifo", "{max_table_files_size=51;ttl=49;allow_compaction=true;}"}})`
Most of the code has been made generic enough so that it could be reused later to make universal options (and other such nested defined-types) dynamic with very few lines of parsing/serializing code changes.
Introduced a few new functions like `ParseStruct`, `SerializeStruct` and `GetStringFromStruct`.
The duplicate code in `GetStringFromDBOptions` and `GetStringFromColumnFamilyOptions` has been moved into `GetStringFromStruct`. So they become just simple wrappers now.
Closes https://github.com/facebook/rocksdb/pull/3006
Differential Revision: D6058619
Pulled By: sagar0
fbshipit-source-id: 1e8f78b3374ca5249bb4f3be8a6d3bb4cbc52f92
Summary:
instad of for specific level -> instead of a specific level
Closes https://github.com/facebook/rocksdb/pull/3040
Differential Revision: D6090811
Pulled By: sagar0
fbshipit-source-id: 499edef0a6f596c448f61791e6aca8f5cce08e9c
Summary:
As discussed on the mailing list (["Skipping entire SSTs while iterating"](https://groups.google.com/forum/#!topic/rocksdb/ujHCJVLrHlU)), this patch adds a `table_filter` to `ReadOptions` that allows specifying a callback to be executed during iteration before each table in the database is scanned. The callback is passed the table's properties; the table is scanned iff the callback returns true.
This can be used in conjunction with a `TablePropertiesCollector` to dramatically speed up scans by skipping tables that are known to contain irrelevant data for the scan at hand.
We're using this [downstream in CockroachDB](https://github.com/cockroachdb/cockroach/blob/master/pkg/storage/engine/db.cc#L2009-L2022) already. With this feature, under ideal conditions, we can reduce the time of an incremental backup in from hours to seconds.
FYI, the first commit in this PR fixes a segfault that I unfortunately have not figured out how to reproduce outside of CockroachDB. I'm hoping you accept it on the grounds that it is not correct to return 8-byte aligned memory from a call to `malloc` on some 64-bit platforms; one correct approach is to infer the necessary alignment from `std::max_align_t`, as done here. As noted in the first commit message, the bug is tickled by having a`std::function` in `struct ReadOptions`. That is, the following patch alone is enough to cause RocksDB to segfault when run from CockroachDB on Darwin.
```diff
--- a/include/rocksdb/options.h
+++ b/include/rocksdb/options.h
@@ -1546,6 +1546,13 @@ struct ReadOptions {
// Default: false
bool ignore_range_deletions;
+ // A callback to determine whether relevant keys for this scan exist in a
+ // given table based on the table's properties. The callback is passed the
+ // properties of each table during iteration. If the callback returns false,
+ // the table will not be scanned.
+ // Default: empty (every table will be scanned)
+ std::function<bool(const TableProperties&)> table_filter;
+
ReadOptions();
ReadOptions(bool cksum, bool cache);
};
```
/cc danhhz
Closes https://github.com/facebook/rocksdb/pull/2265
Differential Revision: D5054262
Pulled By: yiwu-arbug
fbshipit-source-id: dd6b28f2bba6cb8466250d8c5c542d3c92785476
Summary:
Blob db insert blob index to base db as kTypeBlobIndex type, to tell apart values written by plain rocksdb or blob db. This is to make it possible to migrate from existing rocksdb to blob db.
Also with the patch blob db garbage collection get away from OptimisticTransaction. Instead it use a custom write callback to achieve similar behavior as OptimisticTransaction. This is because we need to pass the is_blob_index flag to DBImpl::Get but OptimisticTransaction don't support it.
Closes https://github.com/facebook/rocksdb/pull/3000
Differential Revision: D6050044
Pulled By: yiwu-arbug
fbshipit-source-id: 61dc72ab9977625e75f78cd968e7d8a3976e3632
Summary:
Previously each time we write a blob we write blog_record_header + key + value + blob_record_footer to blob log. The footer only contains a sequence and a crc for the sequence number. The sequence number was used in garbage collection to verify the value is recent. After #2703 we moved to use optimistic transaction and no longer use sequence number from the footer. Remove the footer altogether.
There's another usage of sequence number and we are keeping it: Each blob log file keep track of sequence number range of keys in it, and use it to check if it is reference by a snapshot, before being deleted.
Closes https://github.com/facebook/rocksdb/pull/3005
Differential Revision: D6057585
Pulled By: yiwu-arbug
fbshipit-source-id: d6da53c457a316e9723f359a1b47facfc3ffe090
