4 ms·

I have plenty of rants about the company's engineering, priorities, etc. I just hate people saying dumb shit. :) Workload QPS is a meaningless number unless

by spimmy 10y ago

I have plenty of rants about the company's engineering, priorities, etc. I just hate people saying dumb shit. :) Workload QPS is a meaningless number unless you know what the workload is. At Parse, we used RocksDB (a LSM tree write optimized storage engine) to get something stupid like 9x faster writes. I don't know where you're seeing 600 QPS ... (we got 100x that if we were optimizing for writes) ... but it still doesn't mean anything unless you know the size of the document, whether it's inserts, queries, updates, whether it's hot spotting on a row, whether the lock is at the collection, document, database, or global, etc. If you're going to switch storage engines, you have to use some sort of capture replay technology or you can not have any confidence in the change. Use what we wrote at Parse: https://github.com/ParsePlatform/flashback https://github.com/ParsePlatform/flashback. We spent ~6 months teasing out bugs in rocksdb, mongodb, the 2.6 query planner rewrite, etc before we even started to make the switch. If you don't do that, you don't get to complain about the results. Sorry.

diziet 10y ago
Spimmy, I am not sure about the context of what you're saying though I agree with the context and feedback of your comments, but I am basing the 600 QPS based on this comment on the blog post linked in the article: >To put things in context, we do approximately ~18.07K operations/minute on one primary server. We have two shards in the cluster so two primary server making it ~36.14K operations/minute. 36,140 / 60 is roughly 600. Confusingly, the opcounter screenshot at the top of the blog shows something close to 3k updates / second with a peak of about 4.5k, though it is not explained. I left a more detailed comment on the clevertap blog regarding the kind of operations they are using. When you talk about benchmarking and high level metrics like QPS, there is a level of thresholds where you can say "you're most likely doing something wrong as you should not be hitting cache limit issues". The reason you will move to WT is because of snappy, generally higher 99.9th percentile performance, higher throughput, much better document based locks, etc. Replaying real data is wonderful and great for preparing for a migration like that. MMAPv1 to WT was a much smoother transition for us than what I imagine MMAPv1 to Rocks would be, though the team at FB including Mark Callaghan has made incredible progress on it.
- spimmy 10y ago
  I'm agreeing with your comment, not arguing with it. The problems we had moving from mmapv1 to rocksdb were almost entirely based on the rewrite of the query planner in 2.6, not the storage engine itself. The WT storage engine is far less mature than RocksDB. Only a very tiny amount of code in the Mongo+Rocks integration is actually new code, it's just the thin layer of glue between mongo and the storage engine API. It was a tricky migration because we made the decision to do it early while so much code was still new in mongo for that version. We wanted to help give feedback on the storage engine API because we had pushed so hard for that feature, and because we were pushing the boundaries of what the mmap engine could ever reasonably be expected to do. (Side note: OMG, anyone who measures their request rate in anything other than per-second is putting up a giant red flag that they don't know what they're doing.)
  - diziet 10y ago
    Right, I knew there was a misunderstanding initially over what company I was referring to (CleverTap, not 10gen/MongoDB) and we were mostly on the same page :) RocksDB is great, WT is getting to be great, both are getting better and have solid teams working on them. LSMs have great use cases, btrees too. 600 QPS you do not blog about.
- spimmy 10y ago
  Oh, I just realized that by "company's engineering" you meant CleverTap, not MongoDB. Got it.

by spimmy 10y ago

diziet 10y ago

Spimmy, I am not sure about the context of what you're saying though I agree with the context and feedback of your comments, but I am basing the 600 QPS based on this comment on the blog post linked in the article: >To put things in context, we do approximately ~18.07K operations/minute on one primary server. We have two shards in the cluster so two primary server making it ~36.14K operations/minute. 36,140 / 60 is roughly 600. Confusingly, the opcounter screenshot at the top of the blog shows something close to 3k updates / second with a peak of about 4.5k, though it is not explained. I left a more detailed comment on the clevertap blog regarding the kind of operations they are using. When you talk about benchmarking and high level metrics like QPS, there is a level of thresholds where you can say "you're most likely doing something wrong as you should not be hitting cache limit issues". The reason you will move to WT is because of snappy, generally higher 99.9th percentile performance, higher throughput, much better document based locks, etc. Replaying real data is wonderful and great for preparing for a migration like that. MMAPv1 to WT was a much smoother transition for us than what I imagine MMAPv1 to Rocks would be, though the team at FB including Mark Callaghan has made incredible progress on it.

spimmy 10y ago
I'm agreeing with your comment, not arguing with it. The problems we had moving from mmapv1 to rocksdb were almost entirely based on the rewrite of the query planner in 2.6, not the storage engine itself. The WT storage engine is far less mature than RocksDB. Only a very tiny amount of code in the Mongo+Rocks integration is actually new code, it's just the thin layer of glue between mongo and the storage engine API. It was a tricky migration because we made the decision to do it early while so much code was still new in mongo for that version. We wanted to help give feedback on the storage engine API because we had pushed so hard for that feature, and because we were pushing the boundaries of what the mmap engine could ever reasonably be expected to do. (Side note: OMG, anyone who measures their request rate in anything other than per-second is putting up a giant red flag that they don't know what they're doing.)
- diziet 10y ago
  Right, I knew there was a misunderstanding initially over what company I was referring to (CleverTap, not 10gen/MongoDB) and we were mostly on the same page :) RocksDB is great, WT is getting to be great, both are getting better and have solid teams working on them. LSMs have great use cases, btrees too. 600 QPS you do not blog about.
spimmy 10y ago
Oh, I just realized that by "company's engineering" you meant CleverTap, not MongoDB. Got it.