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https://issues.apache.org/jira/browse/PHOENIX-5502?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=16942343#comment-16942343
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Geoffrey Jacoby commented on PHOENIX-5502:
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The advantage to this is that if you have rows in the index which should have
been deleted but weren't (or were added mistakenly) they get removed and you
end up with a correct index if the rebuild succeeds. The downside is that if
the rebuild fails, you're probably worse off than you were before.
> ALTER INDEX REBUILD removes all rows from already valid/consistent index
> ------------------------------------------------------------------------
>
> Key: PHOENIX-5502
> URL: https://issues.apache.org/jira/browse/PHOENIX-5502
> Project: Phoenix
> Issue Type: Bug
> Affects Versions: 4.14.1, 4.14.2, 4.14.3
> Reporter: Priyank Porwal
> Priority: Major
> Fix For: 4.14.1, 4.14.2, 4.14.3
>
>
> Create Table & Indexes:
> CREATE TABLE DEMO2.PEOPLE (FNAME VARCHAR NOT NULL, LNAME VARCHAR, AGE
> TINYINT, ZIP INTEGER, CONSTRAINT pk PRIMARY KEY (FNAME, LNAME));
> CREATE INDEX PEOPLE_BY_ZIP ON DEMO2.PEOPLE(ZIP);
> CREATE INDEX PEOPLE_BY_AGE ON DEMO2.PEOPLE(AGE);
> Populate Data:
> UPSERT INTO DEMO2.PEOPLE VALUES ('Audi', 'Q5', 15, 65000);
> UPSERT INTO DEMO2.PEOPLE VALUES ('Volkswagon', 'Beetle', 10, 43130);
> UPSERT INTO DEMO2.PEOPLE VALUES ('BMW', 'X3', 4, 15030);
> Query Index:
> SELECT * FROM DEMO2.PEOPLE_BY_AGE;
> <3 rows show up>
> Rebuild Index:
> alter index people_by_age on DEMO2.people rebuild;
> Query Index Again:
> SELECT * FROM DEMO2.PEOPLE_BY_AGE;
> <No rows show up>
>
> It seems that if the index is already consistent, then the rebuild command
> removes all the index rows. Above is the simpler repro, but I have noticed
> similar behavior where rebuild command does the right thing first time on an
> inconsistent index (caused by truncation of table using hbase shell), but
> second run of rebuild command removes all the rows.
>
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