Vladimir Pligin created IGNITE-23120:
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Summary: Improve inline index feature
Key: IGNITE-23120
URL: https://issues.apache.org/jira/browse/IGNITE-23120
Project: Ignite
Issue Type: Improvement
Reporter: Vladimir Pligin
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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