Every decent benchmark can reveal not only performance or stability problems, but oftentimes more subtle issues like less known or undocumented options, common misconfigurations or misunderstandings. Sometimes it can reveal scenarios that a product hasn’t considered before or for which it has different solutions.
What can be learned from the Hypertable vs HBase benchmark from the HBase perspective?
Michael Stack: That we need to work on our usability; even a smart fellow like Doug Judd can get it really wrong.
We haven’t done his sustained upload in a good while. Our defaults need some tweaking.
We need to do more documentation around JVM tuning; you’d think fellas would have grok’d by now that big java apps need their JVM’s tweaked but it looks like the message still hasn’t gotten out there.
That we need a well-funded PR dept. to work on responses to the likes of Doug’s article (well-funded because Doug claims he spent four months on his comparison).
Jean-Daniel Cryans: I already opened a few jiras after using HT’s test on a cluster I have here with almost the same hardware and node count, it’s mostly about usability and performance for that type of use case:
- Automagically tweak global memstore and block cache sizes based on workload
Hypertable does a neat thing where it changes the size given to the CellCache (our MemStores) and Block Cache based on the workload. If you need an image, scroll down at the bottom of this link:
- Soft limit for eager region splitting of young tables
Coming out of HBASE-2375, we need a new functionality much like hypertable’s where we would have a lower split size for new tables and it would grow up to a certain hard limit. This helps usability in different ways:
- With that we can set the default split size much higher and users will still have good data distribution
- No more messing with force splits
- Not mandatory to pre-split your table in order to get good out of the box performance
The way Doug Judd described how it works for them, they start with a low value and then double it every time it splits. For example if we started with a soft size of 32MB and a hard size of 2GB, it wouldn’t be until you have 64 regions that you hit the ceiling.
On the implementation side, we could add a new qualifier in .META. that has that soft limit. When that field doesn’t exist, this feature doesn’t kick in. It would be written by the region servers after a split and by the master when the table is created with 1 region.
- Consider splitting after flushing
Spawning this from HBASE-2375, I saw that it was much more efficient compaction-wise to check if we can split right after flushing. Much like the ideas that Jon spelled out in the description of that jira, the window is smaller because you don’t have to compact and then split right away to only compact again when the daughters open.
If someone is faced with similar scenarios are there workarounds or different solutions?
Michael Stack: There are tunings of HBase configs over in our reference guide for the sustained upload both in hbase and in jvm.
Then there is our bulk load facility which by-passes this scenario altogether which is what we’d encourage folks to use because its 10x to 100x faster getting your data in there.
Jean-Daniel Cryans: You can import 5TB in HBase with sane configs, I’ve done it a few times already since I started using his test. The second time he ran his test he just fixed mslab but still kept the crazy ass other settings like 80% of the memory dedicated to memstores. My testing also shows that you need to keep the eden space under control, 64MB seems a good value in my testing (he didn’t set any in his test, the first time I ran mine without setting it I got the concurrent mode failure too).
The answer he gave this week to Todd’s email on the hadoop mailing list is about a constant stream of updates and that’s what he’s trying to test. Considering that the test imports 5TB in ~16h (on my cluster), you run out of disk space in about 3 days. I seriously don’t know what he’s aiming for here.
Quoting him: “Bulk loading isn’t always an option when data is streaming in from a live application. Many big data use cases involve massive amounts of smaller items in the size range of 10-100 bytes, for example URLs, sensor readings, genome sequence reads, network traffic logs, etc.”
What are the most common places to look for improving the performance of a HBase cluster?
Michael Stack: This is what we point folks at when they ask the likes of the above question: HBase Performance Tunning
If that chapter doesn’t have it, its a bug and we need to fix up our documentation more.
Jean-Daniel Cryans: What Stack said. Also if you run into GC issues like he did then you’re doing it wrong.
I think HBase should find all of this challenging and flattering. Challenging because we know how we can do better along the dimensions of your testing and you are kicking us pretty hard. Flattering because by inference we seem to be worth kicking.
But this misses the point, and reduces what should be a serious discussion of the tradeoffs between Java and C++ to a cariacture. Furthermore, nobody sells HBase. (Not in the Hypertable or Datastax sense. Commercial companies bundle HBase but they do so by including a totally free and zero cost software distribution.) Instead it is voluntarily chosen for hundreds of large installations all over the world, some of them built and run by the smartest guys I have ever encountered in my life. Hypertable would have us believe we are all making foolish choices. While it is true that we all on some level have to deal with the Java heap, only Hypertable seems to not be able to make it work. I find that unsurprising. After all, until you can find some way to break it, you don’t have any kind of marketing story.
This remineded me of the quote from Jonathan Ellis’s Dealing With JVM Limitations in Apache Cassandra:
Cliff Click: Many concurrent algorithms are very easy to write with a GC and totally hard (to down right impossible) using explicit free.
As I was expecting, there are quite a few good things that will come out from this benchmark for both long time HBase users, but also for new adopters.
Original title and link: What HBase Learned From the Hypertable vs HBase Benchmark (©myNoSQL)