Right now we're mostly running with noop for our most recently installed SSDs. Some older ones are running with cfq.
Early on in the development of samza-kv, I tried deadline and noop (in place of cfq) and didn't notice a significant change in performance. However, I don't have any numbers to back this up, so this observation is probably worthless. :) That was also when we were still using LevelDB backed KV and a different SSD model and brand, so I agree that testing the different schedulers (mostly noop vs deadline) is worth revisiting. -Jon On Jan 25, 2015, at 12:29 PM, Roger Hoover <roger.hoo...@gmail.com> wrote: > FYI, for Linux with SSDs, changing the io scheduler to deadline or noop can > make a 500x improvement. I haven't tried this myself. > > http://www.elasticsearch.org/guide/en/elasticsearch/guide/current/hardware.html#_disks > > On Tue, Jan 20, 2015 at 9:28 AM, Chris Riccomini < > criccom...@linkedin.com.invalid> wrote: > >> Hey Roger, >> >> We did some benchmarking, and discovered very similar performance to what >> you've described. We saw ~40k writes/sec, and ~20 k reads/sec, >> per-container, on a Virident SSD. This was without any changelog. Are you >> using a changelog on the store? >> >> When we attached a changelog to the store, the writes dropped >> significantly (~1000 writes/sec). When we hooked up VisualVM, we saw that >> the container was spending > 99% of its time in KafkaSystemProducer.send(). >> >> We're currently doing two things: >> >> 1. Working with our performance team to understand and tune RocksDB >> properly. >> 2. Upgrading the Kafka producer to use the new Java-based API. (SAMZA-227) >> >> For (1), it seems like we should be able to get a lot higher throughput >> from RocksDB. Anecdotally, we've heard that RocksDB requires many threads >> in order to max out an SSD, and since Samza is single-threaded, we could >> just be hitting a RocksDB bottleneck. We won't know until we dig into the >> problem (which we started investigating last week). The current plan is to >> start by benchmarking RocksDB JNI outside of Samza, and see what we can >> get. From there, we'll know our "speed of light", and can try to get Samza >> as close as possible to it. If RocksDB JNI can't be made to go "fast", >> then we'll have to understand why. >> >> (2) should help with the changelog issue. I believe that the slowness with >> the changelog is caused because the changelog is using a sync producer to >> send to Kafka, and is blocking when a batch is flushed. In the new API, >> the concept of a "sync" producer is removed. All writes are handled on an >> async writer thread (though we can still guarantee writes are safely >> written before checkpointing, which is what we need). >> >> In short, I agree, it seems slow. We see this behavior, too. We're digging >> into it. >> >> Cheers, >> Chris >> >> On 1/17/15 12:58 PM, "Roger Hoover" <roger.hoo...@gmail.com> wrote: >> >>> Michael, >>> >>> Thanks for the response. I used VisualVM and YourKit and see the CPU is >>> not being used (0.1%). I took a few thread dumps and see the main thread >>> blocked on the flush() method inside the KV store. >>> >>> On Sat, Jan 17, 2015 at 7:09 AM, Michael Rose <elementat...@gmail.com> >>> wrote: >>> >>>> Is your process at 100% CPU? I suspect you're spending most of your >>>> time in >>>> JSON deserialization, but profile it and check. >>>> >>>> Michael >>>> >>>> On Friday, January 16, 2015, Roger Hoover <roger.hoo...@gmail.com> >>>> wrote: >>>> >>>>> Hi guys, >>>>> >>>>> I'm testing a job that needs to load 40M records (6GB in Kafka as >>>> JSON) >>>>> from a bootstrap topic. The topic has 4 partitions and I'm running >>>> the >>>> job >>>>> using the ProcessJobFactory so all four tasks are in one container. >>>>> >>>>> Using RocksDB, it's taking 19 minutes to load all the data which >>>> amounts >>>> to >>>>> 35k records/sec or 5MB/s based on input size. I ran iostat during >>>> this >>>>> time as see the disk write throughput is 14MB/s. >>>>> >>>>> I didn't tweak any of the storage settings. >>>>> >>>>> A few questions: >>>>> 1) Does this seem low? I'm running on a Macbook Pro with SSD. >>>>> 2) Do you have any recommendations for improving the load speed? >>>>> >>>>> Thanks, >>>>> >>>>> Roger >>>>> >>>> >> >>
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