Thank You James. That's great news that 4.13 for CDH is coming. I will try the same on the new version once its released. 


Thanks,

Jins George


From: James Taylor <jamestaylor@apache.org>
Sent: Tuesday, December 19, 2017 5:38:38 PM
To: user
Subject: Re: Efficient way to get the row count of a table
 
The count would change when a major compaction is done. Back in 4.7, it may have changed when a split occurs too (but this is no longer the case). I'd recommend moving to a newer version: 4.7 was release almost two years ago and is six releases back from the current 4.13 release. FWIW, we're getting ready to release a 4.13 for CDH.

On Tue, Dec 19, 2017 at 4:27 PM, Jins George <jins.george@aeris.net> wrote:
Thank you James and Mujtaba  for the responses.

I am OK with an estimate count . So using SYSTEM.STATS table looks good in my case. But when I tried this, it gave me inconsistent results.  for example.

Time 1:
select count(*) from myschema.mytable  => 3474085
select sum(guide_posts_row_count) from system.stats where physical_name = 'myschema.device_data'  => 3348090

Time 2 : ( Time1 + ~10 mins)
select count(*) from myschema.mytable  => 3474106
select sum(guide_posts_row_count) from system.stats where physical_name = 'myschema.device_data'  => 3348080

So I was expecting the stats count to go up but surprisingly, the count went down.  Is there a specific configuration or something else that I am missing?

I am using phoenix 4.7( on CDH), So cannot try Table sampling feature.

Thanks,
Jins George



On 12/19/2017 03:43 PM, Mujtaba Chohan wrote:

On Tue, Dec 19, 2017 at 3:18 PM, James Taylor <jamestaylor@apache.org> wrote:
If it needs to be 100% accurate, then count(*) is the only way. If your data is write-once data, you might be able to track the row count at the application level through some kind of atomic counter in a different table (but this will likely be brittle). If you can live with an estimate, you could enable statistics [1], optionally configuring Phoenix not to use stats for parallelization [2], and query the SYSTEM.STATS table to get an estimate [3]. 

Another interesting alternative if you want the approximate row count when you have a where clause would be to use the new table sampling feature [4]. You'd also want stats enabled for this to be more accurate too.

Thanks,
James


[2] phoenix.use.stats.parallelization=false
[3] select sum(GUIDE_POSTS_ROW_COUNT) from SYSTEM.STATS where physical_name='my_schema.my_table' 
     and COLUMN_FAMILY='my_first_column_family' -- necessary only if you have multiple column families

On Tue, Dec 19, 2017 at 2:57 PM, Jins George <jins.george@aeris.net> wrote:
Hi,

Is there a way to get the total row count of a phoenix table without running select count(*) from table ?
my use case is to monitor the record count in a table every x minutes, so didn't want to put load on the system by running a select count(*) query.

Thanks,
Jins George