In 0.94.11 Release, has been included an optimization for MultiGets:
https://issues.apache.org/jira/browse/HBASE-9087
What version have you deployed?
On 08/29/2013 01:29 AM, lars hofhansl wrote:
A 1s SLA is tough in HBase (or any large memory JVM application).
Maybe, if you presplit your table, play with JDK7 and the G1 collector, but
nobody here will vouch for such an SLA in the 99th percentile.
I heard some folks have experimented with 30GB heaps and G1 and have reported
max GC times of 200ms, but I have not verified that.
-- Lars
----- Original Message -----
From: Saurabh Yahoo <saurabh...@yahoo.com>
To: "user@hbase.apache.org" <user@hbase.apache.org>
Cc: "user@hbase.apache.org" <user@hbase.apache.org>
Sent: Wednesday, August 28, 2013 3:17 PM
Subject: Re: experiencing high latency for few reads in HBase
Hi Vlad,
Thanks for your response.
1. Our SLA is less than one sec. we cannot afford latency more than 1 sec.
We can increase heap size if that help, we have enough memory on server. What
would be the optimal heap size?
2. Cache hit ratio is 95%. One thing I don't understand that we have allocated
only 4gb for block cache out of 12gb. That left 8gb for rest of JVM. There is
no write. Memcache is empty. Is 8gb not enough for hbase to process the
requests? What are the most memory consuming objects in region server?
3. We will change the cf to IN_memory and report back performance difference.
Thanks,
Saurabh.
On Aug 28, 2013, at 3:15 PM, Vladimir Rodionov <vrodio...@carrieriq.com> wrote:
1. 4 sec max latency is not that bad taking into account 12GB heap. It can be
much larger. What is your SLA?
2. Block evictions is the result of a poor cache hit rate and the root cause of
a periodic stop-the-world GC pauses (max latencies
latencies you have been observing in the test)
3. Block cache consists of 3 parts (25% young generation, 50% - tenured, 25% -
permanent). Permanent part is for CF with
IN_MEMORY = true (you can specify this when you create CF). Block first stored
in 'young gen' space, then gets promoted to 'tenured gen' space
(or gets evicted). May be your 'perm gen' space is underutilized? This is exact
25% of 4GB (1GB). Although HBase LruBlockCache should use all the space
allocated for block cache -
there is no guarantee (as usual). If you don have in_memory column families you
may decrease
Best regards,
Vladimir Rodionov
Principal Platform Engineer
Carrier IQ, www.carrieriq.com
e-mail: vrodio...@carrieriq.com
________________________________________
From: Saurabh Yahoo [saurabh...@yahoo.com]
Sent: Wednesday, August 28, 2013 5:10 AM
To: user@hbase.apache.org
Subject: experiencing high latency for few reads in HBase
Hi,
We are running a stress test in our 5 node cluster and we are getting the
expected mean latency of 10ms. But we are seeing around 20 reads out of 25
million reads having latency more than 4 seconds. Can anyone provide the
insight what we can do to meet below second SLA for each and every read?
We observe the following things -
1. Reads are evenly distributed among 5 nodes. CPUs remain under 5% utilized.
2. We have 4gb block cache (30% block cache out of 12gb) setup. 3gb block cache
got filled up but around 1gb remained free. There are a large number of cache
eviction.
Questions to experts -
1. If there are still 1gb of free block cache available, why is hbase evicting
the block from cache?
4. We are seeing memory went up to 10gb three times before dropping sharply to
5gb.
Any help is highly appreciable,
Thanks,
Saurabh.
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