1447bb5919
Summary:
This diff fixes 2 hacks:
* The callback function can modify the existing value inplace, if the merged value fits within the existing buffer size. But currently the existing buffer size is not being modified. Now the callback recieves a int* allowing the size to be modified. Since size is encoded as a varint in the internal key for memtable. It might happen that the entire value might have be copied to the new location if the new size varint is smaller than the existing size varint.
* The callback function has 3 functionalities
1. Modify existing buffer inplace, and update size correspondingly. Now to indicate that, Returns 1.
2. Generate a new buffer indicating merged value. Returns 2.
3. Fails to do either of above, based on whatever application logic. Returns 0.
Test Plan: Just make all for now. I'm adding another unit test to test each scenario.
Reviewers: dhruba, haobo
Reviewed By: haobo
CC: leveldb, sdong, kailiu, xinyaohu, sumeet, danguo
Differential Revision: https://reviews.facebook.net/D15195
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-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 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 and github wiki (https://github.com/facebook/rocksdb/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.
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.
Design discussions are conducted in https://www.facebook.com/groups/rocksdb.dev/