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Posted to dev@hive.apache.org by Daniel Einspanjer <de...@mozilla.com> on 2010/09/12 04:00:39 UTC
Question regarding region scans in HBase integration
I was trying to spend a little time this weekend catching up with the
current state of HBase integration for Hive. One thing that I haven't
seen mentioned is how exactly Hive scans an HBase table during a SELECT.
Does Hive have logic that allows it to intelligently scan only the
participating regions during a SELECT query that uses the rowkey? If
not, I recently wrote some code that allows a MapReduce job to
effectively select the regions based on a list of start/end rowkey
ranges. If this might be useful to the Hive integration, I could create
a Jira and take a look at trying to set up a patch.
Daniel Einspanjer
Metrics Architect
Mozilla Corporation
Re: Question regarding region scans in HBase integration
Posted by John Sichi <js...@facebook.com>.
I've uploaded a patch for review:
http://review.cloudera.org/r/823/diff
And updated the design doc:
http://wiki.apache.org/hadoop/Hive/FilterPushdownDev
CC'ing a few people who've been working on storage handlers.
JVS
On Sep 12, 2010, at 7:51 PM, John Sichi wrote:
I see. My changes are starting out super-simple, addressing only the case of an equality predicate and a simple key. Once I get those committed, we can talk about how to add support for compound keys and range predicates, which is where your code could come in.
JVS
On Sep 11, 2010, at 7:26 PM, Daniel Einspanjer wrote:
Okay, that getSplits part is specifically where my code was involved.
My use case was one of salted rowkeys. We are storing documents that have a guid as the id and the creation date of the document is important for scanning. When we tested having a rowkey format of <creationtimestamp>+<guid>, the RegionServer hotspots became problematic, so we decided to salt the rowkey by using the first digit of the guid: <hexchar>+<creationtimestamp>+<guid>. This gives us nice distribution of inserts throughout the cluster, but of course, it makes scanning a contiguous date range much more complicated.
The code I have allows us to write a MR that takes a list of prefixes (e.g. the hexchar) and a list of ranges (e.g. the desired timestamps) and construct a master Scan object that contains any configuration such as filters or cache settings, and a series of Scan objects that constitute the Cartesian product of the ranges. Then, it passes those in to a custom getSplits that ensures only the needed regions participate in the Map.
If this sounds like it might be useful, I'll work on getting it cleaned up and posted somewhere so you can review it and maybe glean it for ideas. If you are already past that point then I apologize for not checking into this sooner. :)
-Daniel
On 9/11/10 7:09 PM, John Sichi wrote:
Hi Daniel,
I'm almost done with this for HIVE-1226; the remaining step I need to finish is to get the filter passed down during getSplits, since the HBase getSplits implementation takes care of figuring out which regions contain the row in question.
JVS
On Sep 11, 2010, at 7:00 PM, Daniel Einspanjer wrote:
I was trying to spend a little time this weekend catching up with the current state of HBase integration for Hive. One thing that I haven't seen mentioned is how exactly Hive scans an HBase table during a SELECT.
Does Hive have logic that allows it to intelligently scan only the participating regions during a SELECT query that uses the rowkey? If not, I recently wrote some code that allows a MapReduce job to effectively select the regions based on a list of start/end rowkey ranges. If this might be useful to the Hive integration, I could create a Jira and take a look at trying to set up a patch.
Daniel Einspanjer
Metrics Architect
Mozilla Corporation
Re: Question regarding region scans in HBase integration
Posted by John Sichi <js...@facebook.com>.
I see. My changes are starting out super-simple, addressing only the case of an equality predicate and a simple key. Once I get those committed, we can talk about how to add support for compound keys and range predicates, which is where your code could come in.
JVS
On Sep 11, 2010, at 7:26 PM, Daniel Einspanjer wrote:
> Okay, that getSplits part is specifically where my code was involved.
>
> My use case was one of salted rowkeys. We are storing documents that have a guid as the id and the creation date of the document is important for scanning. When we tested having a rowkey format of <creationtimestamp>+<guid>, the RegionServer hotspots became problematic, so we decided to salt the rowkey by using the first digit of the guid: <hexchar>+<creationtimestamp>+<guid>. This gives us nice distribution of inserts throughout the cluster, but of course, it makes scanning a contiguous date range much more complicated.
>
> The code I have allows us to write a MR that takes a list of prefixes (e.g. the hexchar) and a list of ranges (e.g. the desired timestamps) and construct a master Scan object that contains any configuration such as filters or cache settings, and a series of Scan objects that constitute the Cartesian product of the ranges. Then, it passes those in to a custom getSplits that ensures only the needed regions participate in the Map.
>
> If this sounds like it might be useful, I'll work on getting it cleaned up and posted somewhere so you can review it and maybe glean it for ideas. If you are already past that point then I apologize for not checking into this sooner. :)
>
> -Daniel
>
> On 9/11/10 7:09 PM, John Sichi wrote:
>> Hi Daniel,
>>
>> I'm almost done with this for HIVE-1226; the remaining step I need to finish is to get the filter passed down during getSplits, since the HBase getSplits implementation takes care of figuring out which regions contain the row in question.
>>
>> JVS
>>
>> On Sep 11, 2010, at 7:00 PM, Daniel Einspanjer wrote:
>>
>>> I was trying to spend a little time this weekend catching up with the current state of HBase integration for Hive. One thing that I haven't seen mentioned is how exactly Hive scans an HBase table during a SELECT.
>>>
>>> Does Hive have logic that allows it to intelligently scan only the participating regions during a SELECT query that uses the rowkey? If not, I recently wrote some code that allows a MapReduce job to effectively select the regions based on a list of start/end rowkey ranges. If this might be useful to the Hive integration, I could create a Jira and take a look at trying to set up a patch.
>>>
>>> Daniel Einspanjer
>>> Metrics Architect
>>> Mozilla Corporation
Re: Question regarding region scans in HBase integration
Posted by Daniel Einspanjer <de...@mozilla.com>.
Okay, that getSplits part is specifically where my code was involved.
My use case was one of salted rowkeys. We are storing documents that
have a guid as the id and the creation date of the document is important
for scanning. When we tested having a rowkey format of
<creationtimestamp>+<guid>, the RegionServer hotspots became
problematic, so we decided to salt the rowkey by using the first digit
of the guid: <hexchar>+<creationtimestamp>+<guid>. This gives us nice
distribution of inserts throughout the cluster, but of course, it makes
scanning a contiguous date range much more complicated.
The code I have allows us to write a MR that takes a list of prefixes
(e.g. the hexchar) and a list of ranges (e.g. the desired timestamps)
and construct a master Scan object that contains any configuration such
as filters or cache settings, and a series of Scan objects that
constitute the Cartesian product of the ranges. Then, it passes those
in to a custom getSplits that ensures only the needed regions
participate in the Map.
If this sounds like it might be useful, I'll work on getting it cleaned
up and posted somewhere so you can review it and maybe glean it for
ideas. If you are already past that point then I apologize for not
checking into this sooner. :)
-Daniel
On 9/11/10 7:09 PM, John Sichi wrote:
> Hi Daniel,
>
> I'm almost done with this for HIVE-1226; the remaining step I need to finish is to get the filter passed down during getSplits, since the HBase getSplits implementation takes care of figuring out which regions contain the row in question.
>
> JVS
>
> On Sep 11, 2010, at 7:00 PM, Daniel Einspanjer wrote:
>
>> I was trying to spend a little time this weekend catching up with the current state of HBase integration for Hive. One thing that I haven't seen mentioned is how exactly Hive scans an HBase table during a SELECT.
>>
>> Does Hive have logic that allows it to intelligently scan only the participating regions during a SELECT query that uses the rowkey? If not, I recently wrote some code that allows a MapReduce job to effectively select the regions based on a list of start/end rowkey ranges. If this might be useful to the Hive integration, I could create a Jira and take a look at trying to set up a patch.
>>
>> Daniel Einspanjer
>> Metrics Architect
>> Mozilla Corporation
Re: Question regarding region scans in HBase integration
Posted by John Sichi <js...@facebook.com>.
Hi Daniel,
I'm almost done with this for HIVE-1226; the remaining step I need to finish is to get the filter passed down during getSplits, since the HBase getSplits implementation takes care of figuring out which regions contain the row in question.
JVS
On Sep 11, 2010, at 7:00 PM, Daniel Einspanjer wrote:
> I was trying to spend a little time this weekend catching up with the current state of HBase integration for Hive. One thing that I haven't seen mentioned is how exactly Hive scans an HBase table during a SELECT.
>
> Does Hive have logic that allows it to intelligently scan only the participating regions during a SELECT query that uses the rowkey? If not, I recently wrote some code that allows a MapReduce job to effectively select the regions based on a list of start/end rowkey ranges. If this might be useful to the Hive integration, I could create a Jira and take a look at trying to set up a patch.
>
> Daniel Einspanjer
> Metrics Architect
> Mozilla Corporation