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https://issues.apache.org/jira/browse/IGNITE-5991?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=16121498#comment-16121498
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Vladimir Ozerov commented on IGNITE-5991:
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After consulting with H2 maintainers [1], the following solution was found:
1) Add {{lazy}} hint to API
2) Apply it only to cases when there is only one map query
3) Set lazy execution flag on mapper on per-query basis through
{{Session.setLazyQueryExecution}}
4) Create new thread pool - query engine obtains locks which must be released
in the same thread
5) Handle {{GridQueryNextPageResponse.allRows == -1}} properly on client's
side, currently it leads to extra {{GridQueryNextPageRequest}}
[1] https://github.com/h2database/h2database/issues/588
> SQL: lazy ResultSet for map query
> ---------------------------------
>
> Key: IGNITE-5991
> URL: https://issues.apache.org/jira/browse/IGNITE-5991
> Project: Ignite
> Issue Type: Improvement
> Components: sql
> Affects Versions: 2.1
> Reporter: Vladimir Ozerov
> Assignee: Vladimir Ozerov
> Priority: Critical
> Fix For: 2.2
>
>
> Currently we move the whole {{ResultSet}} to memory when executing SQL query
> on mapper. If result set is large enough, this could easily bring server down
> due to high GC pressure or even OOME.
> To avoid that we should stream H2's {{ResultSet}} to our own consumer, which
> will construct a page and send it to the client When a page is sent,
> consumer will block current thread until "next page request" is received.
> This approach has disadvantage - query thread will be blocked. However,
> implementation should be fairly easy and will allow us to avoid OOMEs on
> server. In future we will improve it to minimize blocking (or even avoid it
> completely).
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