5237b39d2e
Summary: Pull Request resolved: https://github.com/facebook/rocksdb/pull/9105 The user contract of SingleDelete is that: a SingleDelete can only be issued to a key that exists and has NOT been updated. For example, application can insert one key `key`, and uses a SingleDelete to delete it in the future. The `key` cannot be updated or removed using Delete. In reality, especially when write-prepared transaction is being used, things can get tricky. For example, a prepared transaction already writes `key` to the memtable after a successful Prepare(). Afterwards, should the transaction rollback, it will insert a Delete into the memtable to cancel out the prior Put. Consider the following sequence of operations. ``` // operation sequence 1 Begin txn Put(key) Prepare() Flush() Rollback txn Flush() ``` There will be two SSTs resulting from above. One of the contains a PUT, while the second one contains a Delete. It is also known that releasing a snapshot can lead to an L0 containing only a SD for a particular key. Consider the following operations following the above block. ``` // operation sequence 2 db->Put(key) db->SingleDelete(key) Flush() ``` The operation sequence 2 can result in an L0 with only the SD. Should there be a snapshot for conflict checking created before operation sequence 1, then an attempt to compact the db may hit the assertion failure below, because ikey_.type is Delete (from a rollback). ``` else if (clear_and_output_next_key_) { assert(ikey_.type == kTypeValue || ikey_.type == kTypeBlobIndex); } ``` To fix the assertion failure, we can skip the SingleDelete if we detect an earlier Delete in the same snapshot interval. Reviewed By: ltamasi Differential Revision: D32056848 fbshipit-source-id: 23620a91e28562d91c45cf7e95f414b54b729748 |
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RocksDB: A Persistent Key-Value Store for Flash and RAM Storage
RocksDB is developed and maintained by Facebook Database Engineering Team. It is built on earlier work on LevelDB by Sanjay Ghemawat (sanjay@google.com) and Jeff Dean (jeff@google.com)
This code is a library that forms the core building block for a fast key-value server, especially suited for storing data on flash drives. It has a Log-Structured-Merge-Database (LSM) design with flexible tradeoffs between Write-Amplification-Factor (WAF), Read-Amplification-Factor (RAF) and Space-Amplification-Factor (SAF). It has multi-threaded compactions, making it especially suitable for storing multiple terabytes of data in a single database.
Start with example usage here: https://github.com/facebook/rocksdb/tree/main/examples
See the github wiki for more explanation.
The public interface is in include/. Callers should not include or
rely on the details of any other header files in this package. Those
internal APIs may be changed without warning.
Design discussions are conducted in https://www.facebook.com/groups/rocksdb.dev/ and https://rocksdb.slack.com/
License
RocksDB is dual-licensed under both the GPLv2 (found in the COPYING file in the root directory) and Apache 2.0 License (found in the LICENSE.Apache file in the root directory). You may select, at your option, one of the above-listed licenses.