Re: Alternative MySQL PEAR DB sequence behavior

"Stig S. Bakken" wrote: > > "Tomas V.V.Cox" wrote: > > > > "Stig S. Bakken" wrote: > > > > > > "Tomas V.V.Cox" wrote: > > > > > > > > "Stig S. Bakken" wrote: Seems that we have "wrote" a lot :) > > > > > Looks good (but I haven't run any concurrency tests), so I'll > > > > > commit it. > > > > > > > > > > > > > We should setup a basic test to use for example "ab" (Apache > > > > Benchmark). > > > > With it is easy to test concurrency problems. > > > > > > I think a good test would be somewhere around 50 simultaneous PHP > > > requests that constantly generate sequence operations (so each request > > > runs for, say, 30 seconds). > > > > > > > I spend some time in this fun thing and done a mini test suite. This a > > bash script (launch.sh) that launchs "n" php processes in background, > > each of them will do "m" requests to the database. The first param is > > the number of process and the second the number of request per process. > > > > In my tests I a good combination of both params was: ./launch.sh 100 100 > > (grater values may eat your resources, be careful). > > > > I know that it won't launch real simultaneous request, but seems to be > > near it (a better sync system is welcome :), also it doesn't provide a > > method to analyze the data. > > Hm, right now all concurrency.php does is to check whether nextId > returns an error. The race condition occurs if the "UPDATE *_seq SET > id=LAST_INSERT_ID(id+1)" statement is not atomic, so that mysqld reads > the current value of the table in request 1, reads the current value is > request 2, and then both update the sequence with the same value, and > both requests think they have gotten unique ids. My idea was to catch the output of the script and search for repeated and non-consecutive values. My fear wasn't with UPDATE, was more with the lock system and delete. I have the idea of using shared memory to better syncronize processes. I know that probably this stuff won't serve too much, but ... Tomas V.V.Cox PD.- I couldn't post here the scripts, so if someone want to get them please drop me a email.