Re: Coprocessors

[James Taylor <jt...@salesforce.com>]

Sudarshan,
Below are the results that Mujtaba put together. He put together two
version of your schema: one with the ATTRIBID as part of the row key
and one with it as a key value. He also benchmarked the query time both
when all of the data was in the cache versus when all of the data was
read off of disk.

Let us know if you have any questions/follow up.

Thanks,

James (& Mujtaba)

          Compute Average over 250K random rows in 1B row table

                                  ATTRIBID in row key
                      Data from HBase cache       Data loaded from disk
Phoenix Skip Scan          1.4 sec                     31 sec
HBase Batched Gets         3.8 sec                     58 sec
HBase Range Scan            -                          10+ min

                                  ATTRIBID as key value
                      Data from HBase cache       Data loaded from disk
Phoenix Skip Scan          1.7 sec                     37 sec
HBase Batched Gets         4.0 sec                     82 sec
HBase Range Scan            -                          10+ min

Details
-------
HBase 0.94.7 Hadoop 1.04
Total number of regions: 30 spread on 4 Region Servers (6 core W3680 Xeon 3.3GHz) with 8GB heap.

Data:
20 FIELDTYPE, 50M OBJECTID for each FIELDTYPE, 10 ATTRIBID. VAL is random integer.

Query:
SELECT AVG(VAL) FROM T1
WHERE OBJECTID IN (250K RANDOM OBJECTIDs) AND FIELDTYPE = 'F1' AND ATTRIBID = '1'

Create table DML:

1. CREATE TABLE IF NOT EXISTS T1 (
        OBJECTID INTEGER NOT NULL,
        FIELDTYPE CHAR(2) NOT NULL,
        ATTRIBID INTEGER NOT NULL,
        CF.VAL INTEGER
        CONSTRAINT PK PRIMARY KEY (OBJECTID,FIELDTYPE,ATTRIBID))
    COMPRESSION='GZ', BLOCKSIZE='4096'

2. CREATE TABLE IF NOT EXISTS T2 (
        OBJECTID INTEGER NOT NULL,
        FIELDTYPE CHAR(2) NOT NULL,
        CF.ATTRIBID INTEGER,
        CF.VAL INTEGER
        CONSTRAINT PK PRIMARY KEY (OBJECTID,FIELDTYPE))
    COMPRESSION='GZ', BLOCKSIZE='4096'

On 04/25/2013 04:19 PM, Sudarshan Kadambi (BLOOMBERG/ 731 LEXIN) wrote:

> James: First of all, this looks quite promising.
>
> The table schema outlined in your other message is correct except that attrib_id will not be in the primary key. Will that be a problem with respect to the skip-scan filter's performance? (it doesn't seem like it...)
>
> Could you share any sort of benchmark numbers? I want to try this out right away, but I've to wait for my cluster administrator to upgrade us from HBase 0.92 first!
>
> ----- Original Message -----
> From: user@hbase.apache.org
> To: user@hbase.apache.org
> At: Apr 25 2013 18:45:14
>
> On 04/25/2013 03:35 PM, Gary Helmling wrote:
>>> I'm looking to write a service that runs alongside the region servers and
>>> acts a proxy b/w my application and the region servers.
>>>
>>> I plan to use the logic in HBase client's HConnectionManager, to segment
>>> my request of 1M rowkeys into sub-requests per region-server. These are
>>> sent over to the proxy which fetches the data from the region server,
>>> aggregates locally and sends data back. Does this sound reasonable or even
>>> a useful thing to pursue?
>>>
>>>
>> This is essentially what coprocessor endpoints (called through
>> HTable.coprocessorExec()) basically do.  (One difference is that there is a
>> parallel request per-region, not per-region server, though that is a
>> potential optimization that could be made as well).
>>
>> The tricky part I see for the case you describe is splitting your full set
>> of row keys up correctly per region.  You could send the full set of row
>> keys to each endpoint invocation, and have the endpoint implementation
>> filter down to only those keys present in the current region.  But that
>> would be a lot of overhead on the request side.  You could split the row
>> keys into per-region sets on the client side, but I'm not sure we provide
>> sufficient context for the Batch.Callable instance you provide to
>> coprocessorExec() to determine which region it is being invoked against.
> Sudarshan,
> In our head branch of Phoenix (we're targeting this for a 1.2 release in
> two weeks), we've implemented a skip scan filter that functions similar
> to a batched get, except:
> 1) it's more flexible in that it can jump not only from a single key to
> another single key, but also from range to range
> 2) it's faster, about 3-4x.
> 3) you can use it in combination with aggregation, since it's a filter
>
> The scan is chunked up by region and only the keys in each region are
> sent, along the lines as you and Gary have described. Then the results
> are merged together by the client automatically.
>
> How would you decompose your row key into columns? Is there a time
> component? Let me walk you through an example where you might have a
> LONG id value plus perhaps a timestamp (it work equally well if you only
> had a single column in your PK). If you provide a bit more info on your
> use case, I can tailor it more exactly.
>
> Create a schema:
>       CREATE TABLE t (key BIGINT NOT NULL, ts DATE NOT NULL, data VARCHAR
> CONSTRAINT pk PRIMARY KEY (key, ts));
>
> Populate your data using our UPSERT statement.
>
> Aggregate over a set of keys like this:
>
>       SELECT count(*) FROM t WHERE key IN (?,?,?) AND ts > ? AND ts < ?
>
> where you bind the ? at runtime (probably building the statement
> programmatically based on how many keys you're binding.
>
> Then Phoenix would jump around the key space of your table using the
> skip next hint feature provided by filters. You'd just use the regular
> JDBC ResultSet to get your count back.
>
> If you want more info and/or a benchmark of seeking over 250K keys in a
> billion row table, let me know.
>
> Thanks,
>
> James