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Summary: flush_on_destroy has a default value of false and the memtable is flushed in the dbimpl-destructor only when that is set to true. Because we want the memtable to be flushed everytime that the destructor is called(db is closed) and the cases where we work with the memtable only are very less it is a good idea to give this a default value of true. Thus the put from ldb wil have its data flushed to disk in the destructor and the next Get will be able to read it when opened with OpenForReadOnly. The reason that ldb could read the latest value when the db was opened in the normal Open mode is that the Get from normal Open first reads the memtable and directly finds the latest value written there and the Get from OpenForReadOnly doesn't have access to the memtable (which is correct because all its Put/Modify) are disabled Test Plan: make all; ldb put and get and scans Reviewers: dhruba, heyongqiang, sheki Reviewed By: heyongqiang CC: kosievdmerwe, zshao, dilipj, kailiu Differential Revision: https://reviews.facebook.net/D8631
rocksdb: A persistent key-value store for flash storage
Authors: The Facebook Database Engineering Team
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.
leveldb: A key-value store
Authors: Sanjay Ghemawat (sanjay@google.com) and Jeff Dean (jeff@google.com)
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/*.h. 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/db.h
Main interface to the DB: Start here
include/options.h
Control over the behavior of an entire database, and also
control over the behavior of individual reads and writes.
include/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/iterator.h
Interface for iterating over data. You can get an iterator
from a DB object.
include/write_batch.h
Interface for atomically applying multiple updates to a database.
include/slice.h
A simple module for maintaining a pointer and a length into some
other byte array.
include/status.h
Status is returned from many of the public interfaces and is used
to report success and various kinds of errors.
include/env.h
Abstraction of the OS environment. A posix implementation of
this interface is in util/env_posix.cc
include/table.h
include/table_builder.h
Lower-level modules that most clients probably won't use directly