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https://issues.apache.org/jira/browse/PHOENIX-4666?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=16408984#comment-16408984
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James Taylor commented on PHOENIX-4666:
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I like the simplicity of your design, [~ortutay], in using the hash as the
cache ID. You could just assume that the cache is already available and react
to the exception you get back by generating the cache if it's not. That way
you'd need no mapping at all (and no central place to check if the cache ID
maps to an existing cache). That flow is already there, but you'd need to add
the logic to generate the cache as the current code assumes that it has already
built the cache (i.e. this handles the situation in which a region splits and
the new RS doesn't have the cache yet).
Some considerations:
- at a minimum, we could have a global config for the TTL of the cache when
this feature is enabled (so that it'd be a different config than the standard
TTL config).
- at the finest granularity, you could even create a new hint that specifies
the TTL so you could specify it per query.
- we'd want to make it clear in documentation that the cache data would be
stale once generated (until the TTL expires it).
- might consider having a new table level property on which this feature could
be enabled (or a table-specific TTL could be specified)
> 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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