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Dhruba Borthakur 9a357847eb Delete non-visible keys during a compaction even in the presense of snapshots.
Summary:
 LevelDB should delete almost-new keys when a long-open snapshot exists.
The previous behavior is to keep all versions that were created after the
oldest open snapshot. This can lead to database size bloat for
high-update workloads when there are long-open snapshots and long-open
snapshot will be used for logical backup. By "almost new" I mean that the
key was updated more than once after the oldest snapshot.

If there were two snapshots with seq numbers s1 and s2 (s1 < s2), and if
we find two instances of the same key k1 that lie entirely within s1 and
s2 (i.e. s1 < k1 < s2), then the earlier version
of k1 can be safely deleted because that version is not visible in any snapshot.

Test Plan:
unit test attached
make clean check

Differential Revision: https://reviews.facebook.net/D6999
2012-11-28 15:47:40 -08:00
db Delete non-visible keys during a compaction even in the presense of snapshots. 2012-11-28 15:47:40 -08:00
doc merge 1.5 2012-08-28 11:43:33 -07:00
hdfs This is the mega-patch multi-threaded compaction 2012-10-19 14:00:53 -07:00
helpers/memenv Fix all warnings generated by -Wall option to the compiler. 2012-11-06 14:07:31 -08:00
include/leveldb Support taking a configurable number of files from the same level to compact in a single compaction run. 2012-11-21 08:37:03 -08:00
java Add LevelDb's JNI wrapper 2012-10-05 13:13:49 -07:00
linters/src Moved FBCode Linter's to LevelDB. 2012-11-28 09:49:01 -08:00
port Make compression options configurable. These include window-bits, level and strategy for ZlibCompression 2012-11-02 11:26:39 -07:00
scribe fix db_test error with scribe logger turned on 2012-08-28 11:22:58 -07:00
snappy Build with gcc-4.7.1-glibc-2.14.1. 2012-09-17 10:56:26 -07:00
table Metrics: record compaction drop's and bloom filter effectiveness 2012-11-09 11:38:45 -08:00
thrift Implement RowLocks for assoc schema 2012-10-03 23:19:01 -07:00
tools Enhance manifest_dump to print each individual edit. 2012-11-19 12:04:35 -08:00
util Fix broken test; some ldb commands can run without a db_ 2012-11-26 11:11:30 -08:00
.arcconfig Moved FBCode Linter's to LevelDB. 2012-11-28 09:49:01 -08:00
.gitignore Fix ldb segfault and use static libsnappy for all builds 2012-11-21 11:07:19 -08:00
AUTHORS reverting disastrous MOE commit, returning to r21 2011-04-19 23:11:15 +00:00
build_detect_platform Fix ldb segfault and use static libsnappy for all builds 2012-11-21 11:07:19 -08:00
build_detect_version Record the version of the source repository that was used to build the leveldb library. 2012-08-24 15:18:43 -07:00
fbcode.gcc471.sh Fix ldb segfault and use static libsnappy for all builds 2012-11-21 11:07:19 -08:00
LICENSE reverting disastrous MOE commit, returning to r21 2011-04-19 23:11:15 +00:00
Makefile Fix all warnings generated by -Wall option to the compiler. 2012-11-06 14:07:31 -08:00
NEWS sync with upstream @ 21409451 2011-05-21 02:17:43 +00:00
README @20776309 2011-04-20 22:48:11 +00:00
README.fb Push release 1.5.5.fb. 2012-11-13 16:28:11 -08:00
TODO A number of smaller fixes and performance improvements: 2011-06-22 02:36:45 +00:00

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