hive-user mailing list archives

Site index · List index
Message view « Date » · « Thread »
Top « Date » · « Thread »
From Dean Wampler <dean.wamp...@thinkbiganalytics.com>
Subject Re: Effecient partitions usage in join
Date Fri, 23 Nov 2012 13:40:54 GMT
A quick suggestion. If the format never changes, you might as well make the
string and SimpleDateFormat object static to eliminate the overhead of
creating them in every call to evaluate.

On Fri, Nov 23, 2012 at 4:50 AM, Bennie Schut <bschut@ebuddy.com> wrote:

> Well this is the udf:****
>
> ** **
>
> package com.ebuddy.dwhhive.udf;****
>
> ** **
>
> import org.apache.hadoop.hive.ql.exec.Description;****
>
> import org.apache.hadoop.hive.ql.exec.UDF;****
>
> import org.apache.hadoop.hive.ql.udf.UDFType;****
>
> import org.apache.hadoop.io.Text;****
>
> ** **
>
> import java.text.SimpleDateFormat;****
>
> import java.util.Calendar;****
>
> ** **
>
> @Description(****
>
>         name = "currentisodate",****
>
>         value = "currentisodate() - Get the current date. Incorrectly made"
> ****
>
>                 + " deterministic to get partition pruning to work."****
>
> )****
>
> ** **
>
> @UDFType(deterministic = true)****
>
> public class CurrentIsoDate extends UDF {****
>
> ** **
>
>     public static Text evaluate() {****
>
>         String pattern = "yyyy-MM-dd";****
>
>         SimpleDateFormat timeFormat = new SimpleDateFormat(pattern);****
>
>         return new
> Text(timeFormat.format(Calendar.getInstance().getTime()));****
>
>     }****
>
> }****
>
> ** **
>
> ** **
>
> And this is how we use it to query the last 30days:****
>
> ADD jar /opt/hive/udf/udf-2.1.2-jar-with-dependencies.jar;****
>
> CREATE TEMPORARY FUNCTION currectisodate AS
> 'com.ebuddy.dwhhive.udf.CurrentIsoDate';****
>
> select count(*) from test where record_date_iso >=
> DATE_SUB(currentisodate(), 30);****
>
> ** **
>
> I’ve always had a preference for iso dates since they sort nicely:
> 2012-11-23 but you can obviously pick your own pattern.****
>
> ** **
>
> ** **
>
> *From:* Dima Datsenko [mailto:dimad@microsoft.com]
> *Sent:* Thursday, November 22, 2012 4:07 PM
> *To:* Bennie Schut; user@hive.apache.org
>
> *Subject:* RE: Effecient partitions usage in join****
>
> ** **
>
> Hi Benny,****
>
>  ****
>
> The udf solution sounds like a plan. Much better than generating hive
> query with hardcoded partition out of table B. Can you please provide a
> sample of what you’re doing there?****
>
>  ****
>
> Thanks,****
>
> Dima****
>
>  ****
>
> *From:* Bennie Schut [mailto:bschut@ebuddy.com <bschut@ebuddy.com>]
> *Sent:* יום ה 22 נובמבר 2012 16:28
> *To:* user@hive.apache.org
> *Cc:* Dima Datsenko
> *Subject:* RE: Effecient partitions usage in join****
>
>  ****
>
> Unfortunately at the moment partition pruning is a bit limited in hive.
> When hive creates the query plan it decides what partitions to use. So if
> you put hardcoded list of partition_id items in the where clause it will
> know what to do. In the case of a join (or a subquery) it would have to run
> the query before it can know what it can prune.  There are obvious
> solutions to this but they are simply not implemented at the moment.****
>
> Generally speaking people try to work around this by not normalizing the
> data. So if you plan on doing a clean star schema with a calendar table
> then do yourself a favor and but the actual date in the fact table and not
> a meaningless key.****
>
> It’s also good to realize you can (in some special cases) work around it
> by using udf’s. I’ve used it once by creating a udf which produced the
> current date which I flagged as deterministic (ugly I know). This causes
> the planner to run the udf during planning and use the result as if it’s a
> constant and thus partition pruning works again. It’s currently the only
> way I know to select x days of data with partition pruning working.****
>
>  ****
>
>  ****
>
> *From:* Dima Datsenko [mailto:dimad@microsoft.com <dimad@microsoft.com>]
> *Sent:* Thursday, November 22, 2012 2:56 PM
> *To:* user@hive.apache.org
> *Subject:* Effecient partitions usage in join****
>
>  ****
>
> Hi Guys,****
>
>  ****
>
> I wonder if you could help me.****
>
>  ****
>
> I have a huge Hive table partitioned by some field. It has thousands of
> partitions.****
>
> Now I have another small table containing tens of partitions id. I’d like
> to get the data only from those partitions.****
>
>  ****
>
> However when I run****
>
> Select * from A join B on (A.partition_id = B.partition_id), ****
>
> It reads all data from A, then from B and on reduce stage performs join.**
> **
>
>  ****
>
> I tried /*+ MAPJOIN*/ it ran faster sparing reduce operation, but still
> read the whole A table.****
>
>  ****
>
> Is there a more efficient way to perform the query w/o reading the whole A
> content?****
>
>  ****
>
>  ****
>
> Thanks****
>
> Dima****
>



-- 
*Dean Wampler, Ph.D.*
thinkbiganalytics.com
+1-312-339-1330

Mime
View raw message