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https://issues.apache.org/jira/browse/IGNITE-23120?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=18021136#comment-18021136
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Filipp Shergalis commented on IGNITE-23120:
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[~timonin.maksim] Hi! Recently I realized that second bug I described (about
ignoring user limits if configuredInlineSize is set) is a feature. It allows
user to configure a larger inline index without increasing limits for all
indexes. It is even documented:)
> Improve inline index feature
> ----------------------------
>
> Key: IGNITE-23120
> URL: https://issues.apache.org/jira/browse/IGNITE-23120
> Project: Ignite
> Issue Type: Improvement
> Reporter: Vladimir Pligin
> Assignee: Filipp Shergalis
> Priority: Major
> Fix For: 2.18
>
> Time Spent: 0.5h
> Remaining Estimate: 0h
>
> Ignite allows index rows to be inlined directly into the page. However, it
> doesn’t guard properly against too big inline size values. Currently, it uses
> {{PageIO.MAX_PAYLOAD_SIZE}} as the maximum allowed value, but this value can
> still be too large, because it does not take the page size and encryption
> (which adds additional bytes to the page header) into account. This possibly
> leads to a bad situation when only one item can fit in one page which can
> lead to BTree performance degradation.
> The following is expected to be done:
> # When inline size for an index is set, a maximum inline size should be
> computed:
> ## Considering we want to have _at least_ 2 items per page, here’s how the
> page layout with max inline size will look like: {{PS = H + L + I + L + I +
> L}} . Where PS - Page Size, H - page header size, L - size of the child link,
> I - item size.
> ## Using the above equation, we get the max possible item size to be equal
> to: {{I = (PS - H - 3L) / 2}} . However, for inline indexes, every item has
> an additional overhead to the actual inlined value (a.k.a payload), which
> depends on MVCC being present.
> ## Taking this into account, the maximum payload size will be equal: {{P =
> (PS - H - 3L) / 2 - X}} , where P - Payload size, X - overhead per item.
> ## In implementation terms, {{PS}} must be computed using the
> {{PageMemory#realPageSize}} which takes encryption overhead into
> account,{{{}H{}}} is equal to {{{}BPlusIo#ITEMS_OFF{}}}, {{L}} is 8 bytes and
> {{X}} depends on the actual {{AbstractH2ExtrasInnerIO}} implementation and
> varies between 8 and 28 bytes.
> # If the configured inline size exceeds the computed maximum size or
> {{PageIO.MAX_PAYLOAD_SIZE}} then an exception must be thrown with a message
> that notifies the user of the incorrect inline size value. Note that this
> should only happen for _new_ indexes, if a nodes is started on top of an
> existing PDS, no exceptions should be thrown and a warning should be printed
> instead, to preserve backwards compatibility.
> # Fix the “Indexed columns of a row cannot be fully inlined into index”
> warning to recommend at most the maximum allowed inline size.
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