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https://issues.apache.org/jira/browse/PHOENIX-4666?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=16408676#comment-16408676
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Maryann Xue commented on PHOENIX-4666:
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Here's my initial thought:
# As opposed to maintaining a map from a subquery to a persistent cache, we
could have a map from "cache_id" to a persistent cache. What we are doing now
for "cache_id" should be good enough - client-side-generated unique id.
# We'll have a certain property to indicate the use of persistent cache, so
that a HashJoinPlan will re-use the "cache_id" (after it being generated on the
first call) without having to re-send and re-build the caches on region servers.
# User will have to hold on to the compiled statement and re-execute it.
# There's no need for a centralized cache management at this point. A region
server will throw a specific Exception if it is unable to find the cache
requested, then on the client side, the sub-query will be re-evaluated and the
cache will broadcasted to all region servers again with the same cache-id.
Not sure if is similar to your version, but would be nice to see whatever you
already have and we can go from there.
> 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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