redis-dump-load

Dumps Redis data sets into a format suitable for long-term storage (currently JSON) and loads data from such dump files back into Redis.

Features

redis-dump-load:

• Supports all Redis data types;
• Dumps TTL and expiration times;
• Can load TTL OR original expiration time for expiring keys;
• Can create pretty/human-readable dumps (keys dumped in sorted order, output indented);
• Can stream data when dumping and loading;
• Can be used as a module in a larger program or as a standalone utility;
• Uses an output format compatible with redis-dump.

Usage

redis-dump-load may be used as a module and also as a command line tool.

Module Usage

redis-dump-load exports a pickle-like interface, namely load, loads, dump and dumps functions. For example:

import redisdl

json_text = redisdl.dumps()

with open('path/to/dump.json', 'w') as f:
    # streams data
    redisdl.dump(f)

json_text = '...'
redisdl.loads(json_text)

with open('path/to/dump.json') as f:
    # streams data if ijson or jsaone are installed
    redisdl.load(f)

See the streaming section below for more information about streaming.

Dump and load methods accept options as keyword arguments:

json_text = redisdl.dumps(encoding='iso-8859-1', pretty=True)

The arguments should always be passed in as keywords, i.e, do not rely on the order in which the parameters are currently listed. Options take string values unless otherwise noted. The options are as follows:

• host: host name or IP address for redis server
• port: port number for redis server
• unix_socket_path: connect to redis via a Unix socket instead of TCP/IP; specify the path to the socket
• password: specify password to connect to redis
• db (integer): redis database to connect to
• encoding: encoding to use for encoding or decoding the data, see Unicode section below
• pretty (boolean, dump only): produce a pretty-printed JSON which is easier to read; currently this makes dump load entire data set into memory rather than stream it
• keys (dump only): only dump keys matching specified pattern
• use_expireat (boolean, load only): use expireat in preference to ttl when loading expiring keys
• empty (boolean, load only): empty the redis data set before loading the data
• streaming_backend (string): streaming backend to use when loading via load method, if ijson or jsaone is installed and streaming is thus used

Command Line Usage

redisdl.py can be used as a command line tool as follows:

# dump database 0
./redisdl.py > dump.json
./redisdl.py -o dump.json

# load into database 0
./redisdl.py -l < dump.json
./redisdl.py -l dump.json

For convenience, redisdl.py can be hard or soft linked as follows:

ln redisdl.py redis-dump
ln redisdl.py redis-load

Now it can be used thusly:

# dump database 0
./redis-dump > dump.json
./redis-dump -o dump.json

# load into database 0
./redis-load < dump.json
./redis-load dump.json

Symlinks work as well. "load" in the executable name triggers the loading mode, "dump" triggers the dumping mode, otherwise the default is to dump and -l option switches into the loading mode.

All options supported by the module API are accepted when redisdl is invoked as a command line tool. The command line options are:

• -h/--help: help text
• -H HOST/--host HOST: specify redis host
• -p PORT/--port PORT: specify redis port
• -s SOCKET_PATH/--socket SOCKET_PATH: connect to Unix socket at the specified path
• -w PASSWORD/--password PASSWORD: password to use when connecting to redis
• -d DATABASE/--db DATABASE: redis database to connect to (integer)
• -k PATTERN/--keys PATTERN (dumping only): dump only keys matching specified glob-style pattern
• -E ENCODING/-encoding ENCODING: specify encoding to use
• -o PATH/--output PATH: write dump to PATH rather than standard output
• -y/--pretty (dumping only): pretty-print JSON
• -A/--use-expireat (loading only): use expireat rather than ttl values in the dump
• -e/--empty (loading only): empty redis data set before loading
• -B BACKEND/--backend BACKEND (loading only): streaming backend to use

Streaming

dump will stream data unless pretty is given and True.

load will stream data if ijson or jsaone is installed. To determine whether redis-dump-load supports streaming data load, examine redisdl.have_streaming_load variable. There are also redisdl.have_ijson and redisdl.have_jsaone variables indicating presence of the respective library.

redis-dump-load prefers ijson over jsaone and does not specify a backend for ijson by default, which as of this writing means that ijson's pure Python backend will be used. To request a specific backend either pass it as follows to the load methods:

redisdl.load(io, streaming_backend='ijson-yajl2')

... or set the desired backend globally as follows:

redisdl.streaming_backend = 'ijson-yajl2'

The backend argument takes form of "library-library backend", e.g.: - ijson selects the default backend of ijson, which currently is the pure Python one. - ijson-yajl2 selects ijson with yajl2 backend. - yajl2 means the same things as ijson-yajl2 for compatibility with older redis-dump-load versions. - jsaone selects the jsaone backend.

Note: Streaming loading is substantially slower than lump loading. To force lump loading of files, read the files in memory and invoke loads rather than load.

jsaone support was added in redis-dump-load version 1.0.

TTL, EXPIRE and EXPIREAT

When dumping, redis-dump-load dumps the TTL values for expiring keys as well as calculated time when the keys will expire (expireat). As Redis does not provide a command to retrieve absolute expiration time of a key, the expiration time is calculated using the current time on the client's system. As such, if the time on the client system is not in sync with time on the system where the Redis server is running, expireat values will be incorrect.

When loading, redis-dump-load by default uses the TTL values in the dump (ttl key) to set expiration times on the keys in preference to expireat values. This will maintain the expiration times of the keys relative to the dump/load time but will change the absolute expiration time of the keys. Using -A/--use-expireat command line option or use_expireat parameter to module functions will make redis-dump-load use expireat values in preference to ttl values, setting expiring keys to expire at the same absolute time as they had before they were dumped (as long as system times are in sync on all machines involved).

Dumping and loading of TTL values and expiration times was added in redis-dump-load version 1.0.

Unicode

Redis operates on bytes and has no concept of Unicode or encodings. JSON operates on (Unicode) strings and cannot serialize binary data. Therefore, redis-dump-load has to encode Unicode strings into byte strings when loading data into Redis and decode byte strings into Unicode strings when dumping data from Redis. By default redis-dump-load uses utf-8 for encoding data sent to Redis and decoding data received from Redis. This behavior matches redis-py, whose default encoding is utf-8. A different encoding can be specified.

dumps returns strings, that is, instances of str on Python 2 and instances of unicode on Python 3.

When dumping to an IO object using dump, and the IO object accepts byte strings (such as when a file is opened in binary mode), redis-dump-load will .encode() the dumped data using the default encoding in effect.

ijson's yajl2 backend can only decode bytes instances, not str. When loading data from a file opened in text mode and using ijson-yajl2, redis-dump-load will encode the file data using utf-8 encoding before passing the data to ijson. If this fails, try opening the file/stream in binary mode.

jsaone can only decode text strings (str instances), not bytes. When loading data from a file opened in binary mode and using jsaone, redis-dump-load will decode the file data using the default encoding. If this fails, you can change the default encoding or open the files in text mode with the encoding appropriately specified in the open() call.

Concurrent Modifications

redis-dump-load does not lock the entire data set it is dumping, because Redis does not provide a way to do so. As a result, modifications to the data set made while a dump is in progress affect the contents of the dump.

Dependencies

• redis-py
• ijson or jsaone (optional, for streaming load)
• simplejson (Python 2.5 only)

Tests

redis-dump-load has a test suite. To run it, install nose and run:

nosetests

There are several tests that check for race conditions and as such take a long time to run. To skip them, invoke nose thusly:

nosetests -a '!slow'

License

Released under the 2 clause BSD license.