Did s3randobj option change between v3.0-17 and v3.0-25

[russki]

We've recently upgraded from v3.0-17 to v3.0-25 and noticed that the test with --s3randobj is no longer sending requests random enough to be uncached

All the runs with --s3randobj option are being successfully cached.

Are we supposed to be specifying some extra parameters for get the old functionality back or is there a bug introduced somewhere between v3.0-17 and v3.0-25

v3.0-25 example cmdline:

/usr/bin/elbencho --s3endpoints ${endpoint} --hosts elbencho-[0-4].elbencho.elbencho.svc.cluster.local --resfile /tmp/results.txt --csvfile /tmp/results.csv --live1n --livecsv /tmp/live_results.csv --liveint 30000 -r -t 40 -s 100m -b 10m -n 0 -N 20 --s3ignoreerrors --s3fastget --infloop --timelimit 900 --s3objprefix 100mb-obj --s3randobj elbencho

v3.0-25 throughput result (cached)

OPERATION   RESULT TYPE         FIRST DONE   LAST DONE
=========== ================    ==========   =========
READ: 0 files/s; 2439 MiB/s; 0 files; 73174 MiB; 200 threads; 4% CPU; 30s
READ: 0 files/s; 2384 MiB/s; 0 files; 144701 MiB; 200 threads; 4% CPU; 1m0s
READ: 0 files/s; 2365 MiB/s; 0 files; 215651 MiB; 200 threads; 4% CPU; 1m30s

v3.0-17 example cmdline:

/usr/bin/elbencho --s3endpoints ${endpoint} --s3key ${s3key} --s3secret ${s3secret} --hosts elbencho-[0-4].elbencho.elbencho.svc.cluster.local --resfile /tmp/results.txt --csvfile /tmp/results.csv --live1n --livecsv /tmp/live_results.csv --liveint 30000 -r -t 40 -s 100m -b 10m -n 0 -N 20 --s3ignoreerrors --s3fastget --infloop --timelimit 900 --s3objprefix 100mb-obj --s3randobj elbencho

v3.0-17 throughput result (uncached)

OPERATION   RESULT TYPE         FIRST DONE   LAST DONE
=========== ================    ==========   =========
READ: 0 files/s; 78 MiB/s; 0 files; 2343 MiB; 200 threads; 1% CPU; 30s
READ: 0 files/s; 78 MiB/s; 0 files; 4697 MiB; 200 threads; 2% CPU; 1m0s
READ: 0 files/s; 78 MiB/s; 0 files; 7059 MiB; 200 threads; 1% CPU; 1m30s

[breuner]

hi @russki ,
this is very surprising, because i'm not aware of any change in behavior for the "--s3randobj" option between those two versions.
how about trying the "--opslog" option to check that the accesses are random as intended?

[breuner]

@russki : does it help if you add --randalgo balanced to the command? i just became aware that the new linear congruential generator for random numbers from v3.0.19 (which was supposed to help with full range coverage) is less random for certain parameters.