94c7f76da0
Summary: Pull Request resolved: https://github.com/facebook/rocksdb/pull/15461 **What:** With `min_tombstones_for_range_conversion` set, an iterator whose view predates an ingestion can delete the ingested keys for good. **Why it matters:** Silent, permanent data loss. `Get` returns the ingested key right after ingestion. After one scan from the older iterator, `Get` returns NotFound, also after flush and reopen. Every MyRocks bulk load with the option set takes this path: MyRocks ingests with `allow_global_seqno=false` and `snapshot_consistency=false` (seqno 0). **Root cause:** - The older iterator does not see the ingested file. It sees the deleted keys on both sides of the file as one run, and inserts a range tombstone at its read sequence number. The tombstone covers the ingested keys. - `ingest_seqno_barrier_` (D102044512) refuses a conversion only when the iterator's sequence number is below the ingested seqno. That misses two cases: 1. The file gets no new seqno: no overlap (seqno 0), `ingest_behind`, or `allow_db_generated_files`. Ingestion does not move the barrier at all (`assigned > 0`). 2. `NewIterator()` references the SuperVersion before it reads the sequence number. If an ingestion and a write happen in between, the iterator reads at a sequence number above the ingested file, with a SuperVersion that does not have it. This also loses files ingested with a new seqno. - Ingestions that flush the memtable are safe: the older iterator's memtable becomes immutable. **Fix:** Barrier on the Version, not only on the sequence number. - After `LogAndApply()`, ingestion records the new Version number on the active memtable (`ingest_version_barrier_`), while it still holds the per-CF `ingest_sst_lock`. - `DBIter` passes the number of the Version it reads. `AddLogicallyRedundantRangeTombstone()` refuses the conversion if that number is below the barrier. - Version numbers only go up, and every later Version of the column family has the ingested files. So the check is true exactly when the iterator cannot see an ingestion into this memtable. Iterators created after the ingestion convert as before. - The seqno barrier stays: it still covers old explicit snapshots that read a newer Version. **Related:** D126796014 (`Disable tombstone conversion for kMemtableTier iterators`) fixes a different trigger of the same feature. Reviewed By: joshkang97, archang19 Differential Revision: D126875720 fbshipit-source-id: 5767b866c6174d791f9ddae78311816300ac49f3
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.
Questions and discussions are welcome on the RocksDB Developers Public Facebook group and email list on Google Groups.
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.