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https://issues.apache.org/jira/browse/PHOENIX-4666?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=16408720#comment-16408720
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Marcell Ortutay commented on PHOENIX-4666:
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Thanks for the input [~maryannxue]. My current implementation is here:
[https://github.com/ortutay23andme/phoenix/tree/4.7.0-HBase-1.1] and in
particular this is my hacky patch:
[https://github.com/ortutay23andme/phoenix/commit/04c96f672eb4bcdccec27f124373be766f8dd5af]
. Instead of a random cache ID it takes a hash of the query statement and uses
that as the cache ID. Each Phoenix client maintains it's own memory of which
cache IDs have already been executed (this is not ideal, but it was easy to
implement this way).
If I'm understanding your proposal, the Phoenix client would attempt to use a
cache ID with the expectation that it exists on region servers. The region
server would throw an exception if the cache ID is not found, which indicates
to Phoenix client that it should evaluate the subquery as usual.
> Add a subquery cache that persists beyond the life of a query
> -------------------------------------------------------------
>
> Key: PHOENIX-4666
> URL: https://issues.apache.org/jira/browse/PHOENIX-4666
> Project: Phoenix
> Issue Type: Improvement
> Reporter: Marcell Ortutay
> Priority: Major
>
> The user list thread for additional context is here:
> [https://lists.apache.org/thread.html/e62a6f5d79bdf7cd238ea79aed8886816d21224d12b0f1fe9b6bb075@%3Cuser.phoenix.apache.org%3E]
> ----
> A Phoenix query may contain expensive subqueries, and moreover those
> expensive subqueries may be used across multiple different queries. While
> whole result caching is possible at the application level, it is not possible
> to cache subresults in the application. This can cause bad performance for
> queries in which the subquery is the most expensive part of the query, and
> the application is powerless to do anything at the query level. It would be
> good if Phoenix provided a way to cache subquery results, as it would provide
> a significant performance gain.
> An illustrative example:
> SELECT * FROM table1 JOIN (SELECT id_1 FROM large_table WHERE x = 10)
> expensive_result ON table1.id_1 = expensive_result.id_2 AND table1.id_1 =
> \{id}
> In this case, the subquery "expensive_result" is expensive to compute, but it
> doesn't change between queries. The rest of the query does because of the
> \{id} parameter. This means the application can't cache it, but it would be
> good if there was a way to cache expensive_result.
> Note that there is currently a coprocessor based "server cache", but the data
> in this "cache" is not persisted across queries. It is deleted after a TTL
> expires (30sec by default), or when the query completes.
> This is issue is fairly high priority for us at 23andMe and we'd be happy to
> provide a patch with some guidance from Phoenix maintainers. We are currently
> putting together a design document for a solution, and we'll post it to this
> Jira ticket for review in a few days.
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