RE: Why "select count("*) from .." hangs ?

[Pieter Callewaert]

Hi Shalab,

Are you using anything in your WHERE clause of the query?
If not, you are doing a full scan of your data. In iteration 8 it will scan 1 
500 000 entries, and the default time out value is pretty low.

If you do select count(*) from traffic_by_day where segment_id = 1 and day = 1 
it should still work (and very fast).

If you really need the count your data is to insert it, and then increment a 
counter with the number of records you inserted.
That way insteady of doing a count(*) you just get the current counter value.

Kind regards,
Pieter

From: shahab [mailto:shahab.mok...@gmail.com]
Sent: dinsdag 25 maart 2014 17:19
To: user@cassandra.apache.org
Subject: Re: Why "select count("*) from .." hangs ?

Thanks.

I run it on a Linux Server,  Dual Processor, Intel(R) Xeon(R) CPU  E5440  @ 
2.83GHz, 4 core each and  8 GM RAM.

Just to give an example of data inserted:
INSERT INTO traffic_by_day(segment_id, day, event_time, traffic_value)
VALUES (100, 84, '2013-04-03 07:02:00', 79);

Here is the schema:

CREATE TABLE traffic_by_day (
  segment_id int,
  day int,
  event_time timestamp,
  traffic_value int,
  PRIMARY KEY ((segment_id, day), event_time)
) WITH
  bloom_filter_fp_chance=0.010000 AND
  caching='KEYS_ONLY' AND
  comment='' AND
  dclocal_read_repair_chance=0.000000 AND
  gc_grace_seconds=864000 AND
  index_interval=128 AND
  read_repair_chance=0.100000 AND
  replicate_on_write='true' AND
  populate_io_cache_on_flush='false' AND
  default_time_to_live=0 AND
  speculative_retry='99.0PERCENTILE' AND
  memtable_flush_period_in_ms=0 AND
  compaction={'class': 'SizeTieredCompactionStrategy'} AND
  compression={'sstable_compression': 'LZ4Compressor'};

On Tue, Mar 25, 2014 at 4:58 PM, Michael Shuler 
<mich...@pbandjelly.org<mailto:mich...@pbandjelly.org>> wrote:
On 03/25/2014 10:36 AM, shahab wrote:
In our application, we need to insert roughly 300000 sensor data
every 30 seconds (basically we need to store time-series data).  I
wrote a simple java code to insert 300000 random data every 30
seconds for 10 iterations, and measured the number of  entries in the
table after each insertion. But after iteration 8,  (i.e. inserting
1500000 sensor data), the "select count(') ...)  throws time-out
exception and doesn't work anymore. I even tried  to execute "select
count(*)..." using Datastax DevCenter GUI, but I got same result.

If you could post your schema, folks may be able to help a bit better. Your C* 
version couldn't hurt.

cqlsh> DESC KEYSPACE $your_ks;

--
Kind regards,
Michael