Riak stalls, leveldb backend
dpirrone-brusse at basho.com
Tue Jan 6 19:29:50 EST 2015
So, the long and short of it is that Riak doesn't handle objects
larger than 2Mb very well at all. We try to be pretty up-front about
this in the documentation (for example) be we're also aware that
sometimes you need to store big objects. Riak CS was actually created
to deal with these exact performance issues, so I'd highly recommend
you take a look at it, if your usecase requires large objects.
When talking specifically about LevelDB, we have some useful
implementation details in our docs. Take special note of the file
sizes and total size limits for Level-0 and Level-1---each file is
limited to 2Mb, and Level-1 will only store up to 10Mb. The disk I/O
required to flush Level-0 and Level-1 completely so that you can write
-- and then compact -- a >10Mb file (as is your case, Andy) adds up
I hope that helps.
 - http://docs.basho.com/riak/latest/dev/using/application-guide/#What-Kind-of-Data-Are-You-Storing-
 - http://docs.basho.com/riak/latest/ops/advanced/backends/leveldb/#Implementation-Details
On Tue, Jan 6, 2015 at 6:01 AM, Sorin Manole <sorin.manole at trustev.com> wrote:
> Hey Andy,
> We had the same issue few days ago. We were getting timeouts when trying to read a key from riak.
> Also we were seeing in the logs a warning about reading/writing a large object. In our case that object was first read from riak and after written back. It was that big (17Mb) because of some load testing that we did.
> We deleted the object and we didn't experience timeouts anymore.
> We tried to repro the issue, so we can be sure it was this and we posted a 20Mb json to the same key and the timeouts came back again, deleted the 20Mb object and everything worked fine again.
> I don't know why this is happening but we can say that this was the issue for our timeouts.
> Maybe someone has a better understanding on this.. I'd like to be in the loop of this conversation if possible.
> On 5 January 2015 at 18:07, Andy Pellett <andy at embed.ly> wrote:
>> Hi all,
>> I've been experiencing stalls where riak won't return any data (queries time out) with my riak cluster. Here are some basic details:
>> - 8 nodes
>> - riak 1.4.10 (upgraded from 1.4.6 -> 1.4.8 -> 1.4.10)
>> - leveldb backend
>> - n_val is 2
>> - allow_mult is false
>> - ec2 i2.2xlarge boxes (8 cores, 61gb ram, 800gb disk space)
>> - about 33% disk space utilization per node
>> The riak cluster will stall for as long as a few minutes at a time, but will otherwise work as expected for hours. There doesn't seem to be an obvious pattern as to when the stalls happen.
>> My first thought was that the stalls may be related to AAE, but I've disabled that via 'riak attach' and the settings file. Sidenote, I still see messages like:
>> 2015-01-05 12:24:04.666 [info] <0.574.0>@riak_kv_entropy_manager:perhaps_log_throttle_change:826 Changing AAE throttle from 0 -> 10 msec/key, based on maximum vnode mailbox size 209 from 'riak-user at riak-host'
>> which makes me question whether AAE is actually turned off.
>> Now I'm leaning towards leveldb compactions being the issue. What can I do to verify this is the issue, and how can I fix it?
>> I see log messages about large objects:
>> 2015-01-05 16:11:28.046 [warning] <0.6398.0>@riak_kv_vnode:encode_and_put_no_sib_check:1830 Writing very large object (11307735 bytes) to <<"BucketName">>/<<"keys_1420466400">>
>> Could these be causing longer-running compactions, or more frequent compactions?
>> Thanks for reading,
>> riak-users mailing list
>> riak-users at lists.basho.com
> Sorin Manole
> Senior Software Engineer, Trustev
> m:+353 86 051 2658 | e:sorin.manole at trustev.com | w:www.trustev.com| a: Trustev Ltd, 2100 Airport Business Park, Cork, Ireland.
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