There is nothing special in the two sstablemetadata outuputs but if the 
timeouts are due to a network split or overwhelmed node or something like that 
you won't see anything here. That said, if you have the keys which produced the 
timeouts then, yes, you can look for a regular pattern (i.e. always the same 
keys?). 

You can find sstables for a given key with nodetool:    nodetool getendpoints 
<keyspace> <cf> <key>Then you can run the following command on one/each node of 
the enpoints:    nodetool getsstables <keyspace> <cf> <key>
If many sstables are shown in the previous command it means that your data is 
fragmented but thanks to LCS this number should be low.
I think the most usefull actions now would be:
 1) Enable DEBUG for o.a.c.db.ConsistencyLevel, it won't spam your log file, 
you will see the following when errors will occur:    - Local replicas 
[<endpoint1>, ...] are insufficient to satisfy LOCAL_QUORUM requirement of X 
live nodes in '<dc>'
    You are using C* 2.1 but you can have a look at the C* 2.2 logback.xml: 
https://github.com/apache/cassandra/blob/cassandra-2.2/conf/logback.xml    I'm 
using it on production, it's better because it creates a separate debug.log 
file with a asynchronous appender.
   Watch out when enabling:       <appender-ref ref="ASYNCDEBUGLOG" />       
Because the default logback configuration set all o.a.c in DEBUG:           
<logger name="org.apache.cassandra" level="DEBUG"/>       Instead you can set:  
      <logger name="org.apache.cassandra" level="INFO"/>   <logger 
name="org.apache.cassandra.db.ConsistencyLevel" level="DEBUG"/>
    Also, if you want to restrict debug.log to DEBUG level only (instead of 
DEBUG+INFO+...) you can add a LevelFilter to ASYNCDEBUGLOG in logback.xml:      
      <filter class="ch.qos.logback.classic.filter.LevelFilter">      
<level>DEBUG</level>      <onMatch>ACCEPT</onMatch>      
<onMismatch>DENY</onMismatch>    </filter>
  Thus, the debug.log file will be empty unless some Consistency issues happen. 
   2) Enable slow queries log at the driver level with a QueryLogger:    
Cluster cluster = ...   // log queries longer than 1 second, see also 
withDynamicThreshold   QueryLogger queryLogger = 
QueryLogger.builder(cluster).withConstantThreshold(1000).build();   
cluster.register(queryLogger);        Then in your driver logback file:         
   <logger name="com.datastax.driver.core.QueryLogger.SLOW" level="DEBUG" />  
3) And/or: you mentioned that you use DSE so you can enable slow queries 
logging in dse.yaml (cql_slow_log_options)
Best,
Romain   

 Le Lundi 5 septembre 2016 20h05, Joseph Tech <jaalex.t...@gmail.com> a écrit :
 

 Attached are the sstablemeta outputs from 2 SSTables of size 28 MB and 52 MB 
(out2). The records are inserted with different TTLs based on their nature ; 
test records with 1 day, typeA records with 6 months, typeB records with 1 year 
etc. There are also explicit DELETEs from this table, though it's much lower 
than the rate of inserts.
I am not sure how to interpret this output, or if it's the right SSTables that 
were picked. Please advise. Is there a way to get the sstables corresponding to 
the keys that timed out, though they are accessible later.
On Mon, Sep 5, 2016 at 10:58 PM, Anshu Vajpayee <anshu.vajpa...@gmail.com> 
wrote:

We have seen read time out issue in cassandra due to high droppable tombstone 
ratio for repository. 
Please check for high droppable tombstone ratio for your repo. 
On Mon, Sep 5, 2016 at 8:11 PM, Romain Hardouin <romainh...@yahoo.fr> wrote:

Yes dclocal_read_repair_chance will reduce the cross-DC traffic and latency, so 
you can swap the values ( https://issues.apache.org/ji ra/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
















 



   



   



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