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https://issues.apache.org/jira/browse/PHOENIX-4757?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=16686892#comment-16686892
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Gerald Sangudi commented on PHOENIX-4757:
-----------------------------------------
[~jamestaylor] - I'm working through your questions. Meanwhile, here's another
scenario:
{code:sql}
CREATE TABLE table1 (
id1 BIGINT NOT NULL,
id2 BIGINT NOT NULL,
val SMALLINT
)
CONSTRAINT pk PRIMARY KEY (id1, id2)
SALT_BUCKETS=16;
SELECT *
FROM table1
WHERE id1 = 5;
{code}
If the salting is on (id1, id2), then all 16 regions must be scanned, and all
rows in those regions must be examined for id1=5.
If the salting is on (id1), then (a) we can compute the salt value sv(5) for
id1=5, and (b) we can scan only regions and rows beginning with [salt=sv(5),
id1=5]. Wouldn't this be beneficial?
I realize we could avoid the salting altogether, but suppose it is needed for
other reasons, e.g. writes.
> composite key salt_buckets
> --------------------------
>
> Key: PHOENIX-4757
> URL: https://issues.apache.org/jira/browse/PHOENIX-4757
> Project: Phoenix
> Issue Type: Improvement
> Affects Versions: 4.11.0
> Reporter: cmd
> Priority: Major
> Fix For: 4.11.0
>
>
> CREATE TABLE IF NOT EXISTS user_events (
> user_id VARCHAR NOT NULL,
> event_type VARCHAR NOT NULL,
> event_time VARCHAR NOT NULL
> event_msg VARCHAR NOT NULL
> event_status VARCHAR NOT NULL
> event_opt VARCHAR NOT NULL
> CONSTRAINT my_pk PRIMARY KEY (user_id,event_type,event_time))
> SALT_BUCKETS=128;
> and my query is:
> 1.select event_type,count(0) from us_population where user_id='xxxx' group
> by event_type
> 2.select count(0) from us_population where user_id='xxxx' and
> event_type='0101'
> 3.select * from us_population where user_id='xxxx' and event_type='0101' and
> event_time>'20180101' and event_time<'20180201' order by event_time limit
> 50,100
> Concurrency query ratio:
> 1:80%
> 2:10%
> 3:10%
> user_events data :50billion
> It can be a field/some fileds of the primary key salted by hash
> grammar with "SALT_BUCKETS(user_id)=4" or
> "SALT_BUCKETS(user_id,event_type)=4"
> ref:
>
> [https://www.safaribooksonline.com/library/view/greenplum-architecture/9781940540337/xhtml/chapter03.xhtml]
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