Yes dclocal_read_repair_chance will reduce the cross-DC traffic and latency, so
you can swap the values ( https://issues.apache.org/jira/browse/CASSANDRA-7320
). I guess the sstable_size_in_mb was set to 50 because back in the day (C*
1.0) the default size was way too small: 5 MB. So maybe someone in your company
tried "10 * the default" i.e. 50 MB. Now the default is 160 MB. I don't say to
change the value but just keep in mind that you're using a small value here, it
could help you someday.
Regarding the cells, the histograms shows an *estimation* of the min, p50, ...,
p99, max of cells based on SSTables metadata. On your screenshot, the Max is
4768. So you have a partition key with ~ 4768 cells. The p99 is 1109, so 99% of
your partition keys have less than (or equal to) 1109 cells. You can see these
data of a given sstable with the tool sstablemetadata.
Best,
Romain
Le Lundi 5 septembre 2016 15h17, Joseph Tech <jaalex.t...@gmail.com> a
écrit :
Thanks, Romain . We will try to enable the DEBUG logging (assuming it won't
clog the logs much) . Regarding the table configs, read_repair_chance must be
carried over from older versions - mostly defaults. I think sstable_size_in_mb
was set to limit the max SSTable size, though i am not sure on the reason for
the 50 MB value.
Does setting dclocal_read_repair_chance help in reducing cross-DC traffic
(haven't looked into this parameter, just going by the name).
By the cell count definition : is it incremented based on the number of writes
for a given name(key?) and value. This table is heavy on reads and writes. If
so, the value should be much higher?
On Mon, Sep 5, 2016 at 7:35 AM, Romain Hardouin <romainh...@yahoo.fr> wrote:
Hi,
Try to put org.apache.cassandra.db. ConsistencyLevel at DEBUG level, it could
help to find a regular pattern. By the way, I see that you have set a global
read repair chance: read_repair_chance = 0.1And not the local read repair:
dclocal_read_repair_chance = 0.0 Is there any reason to do that or is it just
the old (pre 2.0.9) default configuration?
The cell count is the number of triplets: (name, value, timestamp)
Also, I see that you have set sstable_size_in_mb at 50 MB. What is the rational
behind this? (Yes I'm curious :-) ). Anyway your "SSTables per read" are good.
Best,
Romain
Le Lundi 5 septembre 2016 13h32, Joseph Tech <jaalex.t...@gmail.com> a
écrit :
Hi Ryan,
Attached are the cfhistograms run within few mins of each other. On the
surface, don't see anything which indicates too much skewing (assuming skewing
==keys spread across many SSTables) . Please confirm. Related to this, what
does the "cell count" metric indicate ; didn't find a clear explanation in the
documents.
Thanks,Joseph
On Thu, Sep 1, 2016 at 6:30 PM, Ryan Svihla <r...@foundev.pro> wrote:
Have you looked at cfhistograms/tablehistograms your data maybe just skewed
(most likely explanation is probably the correct one here)
Regard,
Ryan Svihla
_____________________________
From: Joseph Tech <jaalex.t...@gmail.com>
Sent: Wednesday, August 31, 2016 11:16 PM
Subject: Re: Read timeouts on primary key queries
To: <user@cassandra.apache.org>
Patrick,
The desc table is below (only col names changed) :
CREATE TABLE db.tbl ( id1 text, id2 text, id3 text, id4 text, f1
text, f2 map<text, text>, f3 map<text, text>, created timestamp,
updated timestamp, PRIMARY KEY (id1, id2, id3, id4)) WITH CLUSTERING ORDER
BY (id2 ASC, id3 ASC, id4 ASC) AND bloom_filter_fp_chance = 0.01 AND
caching = '{"keys":"ALL", "rows_per_partition":"NONE"}' AND comment = ''
AND compaction = {'sstable_size_in_mb': '50', 'class':
'org.apache.cassandra.db. compaction. LeveledCompactionStrategy'} AND
compression = {'sstable_compression': 'org.apache.cassandra.io.
compress.LZ4Compressor'} AND dclocal_read_repair_chance = 0.0 AND
default_time_to_live = 0 AND gc_grace_seconds = 864000 AND
max_index_interval = 2048 AND memtable_flush_period_in_ms = 0 AND
min_index_interval = 128 AND read_repair_chance = 0.1 AND
speculative_retry = '99.0PERCENTILE';
and the query is select * from tbl where id1=? and id2=? and id3=? and id4=?
The timeouts happen within ~2s to ~5s, while the successful calls have avg of
8ms and p99 of 15s. These times are seen from app side, the actual query times
would be slightly lower.
Is there a way to capture traces only when queries take longer than a specified
duration? . We can't enable tracing in production given the volume of traffic.
We see that the same query which timed out works fine later, so not sure if the
trace of a successful run would help.
Thanks,Joseph
On Wed, Aug 31, 2016 at 8:05 PM, Patrick McFadin <pmcfa...@gmail.com> wrote:
If you are getting a timeout on one table, then a mismatch of RF and node count
doesn't seem as likely.
Time to look at your query. You said it was a 'select * from table where key=?'
type query. I would next use the trace facility in cqlsh to investigate
further. That's a good way to find hard to find issues. You should be looking
for clear ledge where you go from single digit ms to 4 or 5 digit ms times.
The other place to look is your data model for that table if you want to post
the output from a desc table.
Patrick
On Tue, Aug 30, 2016 at 11:07 AM, Joseph Tech <jaalex.t...@gmail.com> wrote:
On further analysis, this issue happens only on 1 table in the KS which has the
max reads.
@Atul, I will look at system health, but didnt see anything standing out from
GC logs. (using JDK 1.8_92 with G1GC).
@Patrick , could you please elaborate the "mismatch on node count + RF" part.
On Tue, Aug 30, 2016 at 5:35 PM, Atul Saroha <atul.sar...@snapdeal.com> wrote:
There could be many reasons for this if it is intermittent. CPU usage + I/O
wait status. As read are I/O intensive, your IOPS requirement should be met
that time load. Heap issue if CPU is busy for GC only. Network health could be
the reason. So better to look system health during that time when it comes.
------------------------------ ------------------------------
------------------------------ ---------------------------
Atul Saroha
Lead Software Engineer
M: +91 8447784271 T: +91 124-415-6069 EXT: 12369
Plot # 362, ASF Centre - Tower A, Udyog Vihar,
Phase -4, Sector 18, Gurgaon, Haryana 122016, INDIA
On Tue, Aug 30, 2016 at 5:10 PM, Joseph Tech <jaalex.t...@gmail.com> wrote:
Hi Patrick,
The nodetool status shows all nodes up and normal now. From OpsCenter "Event
Log" , there are some nodes reported as being down/up etc. during the timeframe
of timeout, but these are Search workload nodes from the remote (non-local) DC.
The RF is 3 and there are 9 nodes per DC.
Thanks,Joseph
On Mon, Aug 29, 2016 at 11:07 PM, Patrick McFadin <pmcfa...@gmail.com> wrote:
You aren't achieving quorum on your reads as the error is explains. That means
you either have some nodes down or your topology is not matching up. The fact
you are using LOCAL_QUORUM might point to a datacenter mis-match on node count
+ RF.
What does your nodetool status look like?
Patrick
On Mon, Aug 29, 2016 at 10:14 AM, Joseph Tech <jaalex.t...@gmail.com> wrote:
Hi,
We recently started getting intermittent timeouts on primary key queries
(select * from table where key=<key>)
The error is : com.datastax.driver.core.excep tions.ReadTimeoutException:
Cassandra timeout during read query at consistency LOCAL_QUORUM (2 responses
were required but only 1 replica
a responded)
The same query would work fine when tried directly from cqlsh. There are no
indications in system.log for the table in question, though there were
compactions in progress for tables in another keyspace which is more frequently
accessed.
My understanding is that the chances of primary key queries timing out is very
minimal. Please share the possible reasons / ways to debug this issue.
We are using Cassandra 2.1 (DSE 4.8.7).
Thanks,Joseph
