mumrah / flake-java

Id generator based on Twitter's Snowflake

Unique Id generator

Based on http://blog.boundary.com/2012/01/12/Flake-A-decentralized-k-ordered-id-generation-service-in-Erlang.html which is in turn based on Twitter's Snowflake project: http://engineering.twitter.com/2010/06/announcing-snowflake.html

Generates unique ids based on the current epoch time, current machine identity, and a counter. The result are mostly ordered unique ids that require no synchronization between machines.

Compile and run

javac -cp .:./lib/uuid-3.2.1-SNAPSHOT.jar:./lib/commons-codec-1.6.jar src/uniq/UniqueId.java
java -cp .:./lib/uuid-3.2.1-SNAPSHOT.jar:./lib/commons-codec-1.6.jar:src uniq.UniqueId

Performance

2011 MacBook Pro, 2.8Ghz i7

Cat to file

$ time java -cp .:./lib/uuid-3.2.1-SNAPSHOT.jar:./lib/commons-codec-1.6.jar:src uniq.UniqueId 10000000 > out

real    0m18.498s
user    0m5.662s
sys     0m12.973s

$ ls -lh out
-rw-r--r--  1 mumrah  staff   153M May 22 10:52 out

540 id/ms

Since each id is 128 bits, the I/O rate comes out to 8640000 bytes per second, or 8.24 MB/s. Compare this to 66.59 MB/s which is the speed that the same system can "yes > omgyes". I guess that order of magnitude difference is the price of safety/synchronization.

Pipe to /dev/null

$ time java -cp .:./lib/uuid-3.2.1-SNAPSHOT.jar:./lib/commons-codec-1.6.jar:src uniq.UniqueId 10000000 > /dev/null

real    0m7.794s
user    0m4.688s
sys     0m3.253s

1280 id/ms

Pipe to fifo, fifo to /dev/null

$ time java -cp .:./lib/uuid-3.2.1-SNAPSHOT.jar:./lib/commons-codec-1.6.jar:src uniq.UniqueId 10000000 > foo

real    0m18.051s
user    0m5.594s
sys     0m12.594s

554 id/ms

flake-java's Issues

overflow ?

Hi,

Not that we will ever need it (i think), but I am curious how the overflow is handled on the sequencenumber within the same millisecond ?

Thanks
Jorg

Generates duplicate IDs when time is not monotonic

We just ran into an issue where duplicate IDs got generated.
I think this is because the code assumes that System.currentTimeMillis() is monotonic, which is not always so