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https://issues.apache.org/jira/browse/IGNITE-7948?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=16771924#comment-16771924
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Ignite TC Bot commented on IGNITE-7948:
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{panel:title=--> Run :: All: No blockers
found!|borderStyle=dashed|borderColor=#ccc|titleBGColor=#D6F7C1}{panel}
[TeamCity *--> Run :: All*
Results|https://ci.ignite.apache.org/viewLog.html?buildId=3113559&buildTypeId=IgniteTests24Java8_RunAll]
> SQL: read only necessary fields into the row when possible
> ----------------------------------------------------------
>
> Key: IGNITE-7948
> URL: https://issues.apache.org/jira/browse/IGNITE-7948
> Project: Ignite
> Issue Type: Task
> Components: sql
> Reporter: Vladimir Ozerov
> Assignee: Taras Ledkov
> Priority: Major
> Fix For: 2.8
>
>
> When H2 row is read, we always fill it with data eagerly through link
> materialization. Materialization is performed under page "read lock" what
> guarantees row-level consistency. This may lead to excessive memory pressure
> due to memory copying. For example, consider a class with 50 fields and a
> query which reads only 2 of them. 48 other fields will be copied without a
> reason. Lazy initialization is not an option because it will only defer
> memcpy, but not eliminate it.
> Instead we can try using H2. It passes {{TableFilter}} class to some of index
> access methods*. We can analyze this class and create the list of required
> fields. Then we can read these fields under read lock from offheap and put
> them to the row.
> In addition to saved memcpy this could give us more benefits:
> 1) No more need for field cache ({{GridH2KeyValueRowOnheap#valCache}})
> 2) No more need to read {{_VER}} column and possibly {{_KEY}} or {{_VAL}}
> But there are a number of drawbacks as well. E.g. it is impossible to read
> strings from offheap efficiently, so queries with VARCHAR will definitely
> suffer from this change.
> \* {{org.h2.index.Index#find(org.h2.table.TableFilter,
> org.h2.result.SearchRow, org.h2.result.SearchRow)}}
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