Thank you Lars,
There must be something wrong with my testing yesterday. I cannot reproduce the
issue anymore. Now, changing the cache.size from 0 to 0.4 will not slow down
the write perf dramatically, but still will slow down write (Yesterday I saw a
7x slowdown, today it is about 1.3x slowdown which is acceptable for me). As
Ted pointed out, it is possible that memstore cannot get enough memory when
more RAM give to block cache so it flush more frequently, but I really need
more reading to understand when memstore will flush.
And one thing I noticed is when I restart hbase for the very first test, the
performance is best, then the second time, it is slower, both read and write,
and slower and slower in the following tests and get to a stable point after
about 3 or 4 times, in each run I will read 5,000,000 rows and update 5,000,000
rows. There are too many factors affect the read/write OPS in hbase...
My purpose is to find a proper way to evaluate performance, since we are going
to change something in hbase and it is good to have a base benchmark so we can
compare the performance after change. So I must make sure the perf test itself
make sense and should be trusted.
I saw an entry in the log may help to see the cache settings in my system:
hfile.LruBlockCache: Total=373.54 MB, free=13.13 MB, max=386.68 MB,
blocks=5655, accesses=17939947, hits=14065015, hitRatio=78.40%, ,
cachingAccesses=17934857, cachingHits=14064420, cachingHitsRatio=78.42%,
evictions=15646, evicted=3861343, evictedPerRun=246.7942657470703
My testing environment is a workstation with 12 core CPU, 96G memory and 1.7 T
disk. But it is a shared workstation, many users share it and I started hbase
in standalone mode with hbase-site.xml as below :
<configuration>
<property>
<name>hbase.rootdir</name>
<value>hdfs://localhost:24400/hbase</value>
</property>
<property>
<name>hbase.zookeeper.property.dataDir</name>
<value>hdfs://localhost:24400/zookeeper</value>
</property>
<property>
<name>hbase.master.port</name>
<value>24560</value>
</property>
<property>
<name>hbase.master.info.port</name>
<value>24561</value>
</property>
<property>
<name>hbase.regionserver.port</name>
<value>24562</value>
</property>
<property>
<name>hbase.regionserver.info.port</name>
<value>24563</value>
</property>
<property>
<name>hbase.zookeeper.peerport</name>
<value>24567</value>
</property>
<property>
<name>hbase.zookeeper.leaderport</name>
<value>24568</value>
</property>
<property>
<name>hbase.zookeeper.property.clientPort</name>
<value>24570</value>
</property>
<property>
<name>hbase.rest.port</name>
<value>24571</value>
</property>
<property>
<name>hbase.client.scanner.caching</name>
<value>100</value>
</property>
<property>
<name>hbase.client.scanner.timeout.period</name>
<value>60000</value>
</property>
<property>
<name>hbase.bulkload.staging.dir</name>
<value>hdfs://localhost:24400/hbase-staging</value>
</property>
<property>
<name>hbase.snapshot.enabled</name>
<value>true</value>
</property>
<property>
<name>hbase.master.distributed.log.splitting</name>
<value>false</value>
</property>
<property>
<name>zookeeper.session.timeout</name>
<value>90000000</value> :-) I just want to make sure never timeout
here, since I get timeout so many times...
</property>
<property>
<name>hfile.block.cache.size</name>
<value>0.4</value>
</property>
</configuration>
[liuliumi@ YCSB]$ free -m
total used free shared buffers cached
Mem: 96731 46828 49903 0 984 32525
-/+ buffers/cache: 13317 83413
Swap: 48432 12 48420
[liuliumi@ YCSB]$ lscpu
Architecture: x86_64
CPU op-mode(s): 32-bit, 64-bit
Byte Order: Little Endian
CPU(s): 12
On-line CPU(s) list: 0-11
Thread(s) per core: 1
Core(s) per socket: 6
Socket(s): 2
NUMA node(s): 2
Vendor ID: GenuineIntel
CPU family: 6
Model: 44
Stepping: 2
CPU MHz: 3065.894
BogoMIPS: 6130.96
Virtualization: VT-x
L1d cache: 32K
L1i cache: 32K
L2 cache: 256K
L3 cache: 12288K
NUMA node0 CPU(s): 0,2,4,6,8,10
NUMA node1 CPU(s): 1,3,5,7,9,11
Thanks,
Ming
-----Original Message-----
From: lars hofhansl [mailto:[email protected]]
Sent: Friday, November 21, 2014 4:31 AM
To: [email protected]
Subject: Re: how to explain read/write performance change after modifying the
hfile.block.cache.size?
That would explain it if memstores are flushed due to global memory pressure.
But cache and memstore size are (unfortunately) configured independently. The
memstore heap portion would be 40% (by default) in either case.So this is a bit
curious still.
Ming, can you tell us more details?- RAM on the boxes- heap setup for the
region servers- any other relevant settings on hbase-site.xml- configs on the
table/column family you're writing to (like bloom filters, etc).
That would help us diagnose this.
-- Lars
From: Ted Yu <[email protected]>
To: "[email protected]" <[email protected]>
Sent: Thursday, November 20, 2014 9:32 AM
Subject: Re: how to explain read/write performance change after modifying the
hfile.block.cache.size?
When block cache size increases from 0 to 0.4, the amount of heap given to
memstore decreases. This would slow down the writes.
Please see:
http://hbase.apache.org/book.html#store.memstore
For your second question, see this thread:
http://search-hadoop.com/m/DHED4TEvBy1/lars+hbase+hflush&subj=Re+Clarifications+on+HBase+Durability
Cheers
On Thu, Nov 20, 2014 at 8:05 AM, Liu, Ming (HPIT-GADSC) <[email protected]>
wrote:
> Hello, all,
>
> I am playing with YCSB to test HBase performance. I am using HBase 0.98.5.
> I tried to adjust the hfile.block.cache.size to see the difference,
> when I set hfile.block.cache.size to 0, read performance is very bad,
> but write performance is very very very good....; when I set
> hfile.block.cache.size to 0.4, read is better, but write performance
> drop dramatically. I disable the client side writebuffer already.
> This is hard to understand for me:
> The HBase guide just said hfile.block.cache.size setting is about how
> much memory used as block cache used by StoreFile. I have no idea of
> how HBase works internally. Typically, it is easy to understand that
> increase the size of cache should help the read, but why it will harm
> the write operation? The write performance down from 30,000 to 4,000
> for your reference, just by changing the hfile.block.cache.size from 0 to 0.4.
> Could anyone give me a brief explanation about this observation or
> give me some advices about what to study to understand what is block cache
> used for?
>
> Another question: HBase write will first write to WAL then to memstore.
> Will the write to WAL go to disk directly before hbase write memstore,
> a sync operation or it is possible that write to WAL is still buffered
> somewhere when hbase put the data into the memstore?
>
> Reading src code may cost me months, so a kindly reply will help me a
> lot... ...
> Thanks very much!
>
> Best Regards,
> Ming
>
