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Summary: This is expected to solve the "gaps in transaction log iterator" problem. * After a lot of observations on the gaps on the sigmafio machines I found that it is due to a race between log reader and writer always. * So when we drop the wormhole subscription and refresh the iterator, the gaps are not there. * It is NOT due to some boundary or corner case left unattended in the iterator logic because I checked many instances of the gaps against their log files with ldb. The log files are NOT corrupted also. * The solution is to not allow the iterator to read incompletely written sequences and detect gaps inside itself and invalidate it which will cause the application to refresh the iterator normally and seek to the required sequence properly. * Thus, the iterator can at least guarantee that it will not give any gaps. Test Plan: * db_test based log iterator tests * db_repl_stress * testing on sigmafio setup to see gaps go away Reviewers: dhruba, haobo Reviewed By: dhruba CC: leveldb Differential Revision: https://reviews.facebook.net/D13593
rocksdb: A persistent key-value store for flash storage
Authors: * The Facebook Database Engineering Team
* Build 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 an Log-Stuctured-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 specially suitable for storing multiple terabytes of data in a
single database.
The core of this code has been derived from open-source leveldb.
The code under this directory implements a system for maintaining a
persistent key/value store.
See doc/index.html for more explanation.
See doc/impl.html for a brief overview of the implementation.
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.
Guide to header files:
include/rocksdb/db.h
Main interface to the DB: Start here
include/rocksdb/options.h
Control over the behavior of an entire database, and also
control over the behavior of individual reads and writes.
include/rocksdb/comparator.h
Abstraction for user-specified comparison function. If you want
just bytewise comparison of keys, you can use the default comparator,
but clients can write their own comparator implementations if they
want custom ordering (e.g. to handle different character
encodings, etc.)
include/rocksdb/iterator.h
Interface for iterating over data. You can get an iterator
from a DB object.
include/rocksdb/write_batch.h
Interface for atomically applying multiple updates to a database.
include/rocksdb/slice.h
A simple module for maintaining a pointer and a length into some
other byte array.
include/rocksdb/status.h
Status is returned from many of the public interfaces and is used
to report success and various kinds of errors.
include/rocksdb/env.h
Abstraction of the OS environment. A posix implementation of
this interface is in util/env_posix.cc
include/rocksdb/table_builder.h
Lower-level modules that most clients probably won't use directly
include/rocksdb/cache.h
An API for the block cache.
include/rocksdb/compaction_filter.h
An API for a application filter invoked on every compaction.
include/rocksdb/filter_policy.h
An API for configuring a bloom filter.
include/rocksdb/memtablerep.h
An API for implementing a memtable.
include/rocksdb/statistics.h
An API to retrieve various database statistics.
include/rocksdb/transaction_log.h
An API to retrieve transaction logs from a database.