Benchmarking Redis

Benchmarking Redis

November 18 2010

2 months ago I started working on an ORM for Redis a key-value database. Now I am about to rewrite parts of it because I didn't test and measure everything beforehand.

This time I decided to measure the performance of the different Redis commands. I want to be sure that any optimizations I might implement really helps.

A Redis database is a big mapping. Its keys are strings and the values can be strings, lists, sets, ordered sets, and hashes. Here I’ll just consider strings and hashes. The 2 types of commands I'm interested in are:

• Set commands: SET, MSET, HMSET, and HSET.
• Get commands: GET, MGET, HMGET, and HGET.

The command prefixed by H are for hashes, the ones without prefix are for regular strings. Commands with an M are the ones that can set or get multiple values. To learn more about how Redis works check out the documentation.

I wrote a little script to test how fast the different commands are depending on the number of items to write or read for each operation. I configured Redis to use the Append-only-file like this:

appendonly yes

appendfsync always

Write operations will surely be faster without it. but that's how I use Redis. I do this because I don’t want to lose data, ever!

Here are the results:

Times are in micro-seconds per items

Read
Elements	GET	HGET	MGET	HMGET
1	167.25	163.04	216.26	203.46
2	164.99	161.72	112.71	109.85
10	156.37	157.34	35.41	33.73
100	156.26	164.23	22.31	19.31
1000	175.82	161.74	31.10	29.56
Write
Elements	SET	HSET	MSET	HMSET
1	816.10	851.05	887.86	902.71
2	908.21	939.67	560.31	587.40
10	965.12	983.00	218.81	227.05
100	945.03	1037.13	120.09	110.63
1000	897.69	901.27	106.49	101.37

Hash operations are a little bit faster than the ones on strings, probably because there are fewer keys in a hash than in the full Redis mapping. The difference is not too significant though.

*SET operations are faster than *MSET operations for a single element, and for 2 elements or more *MSET operations are faster. No surprise here. But something worth noting is that *MSET operations are MUCH faster than *SET operations with 2 or more elements. They can be as much as 5 times faster when reading and 9 times faster when writing. Something to keep in mind when you have to update 5000 keys in a single batch.