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https://issues.apache.org/jira/browse/PHOENIX-4232?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=16184538#comment-16184538
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James Taylor commented on PHOENIX-4232:
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I think a filter would work fine for the case where the shadow cells already
exist. However, it won't work for the case in which you need to lookup in the
commit table because you won't have the state you need to create a scanner. You
could have your own coprocessor that hides this, though. The downside of this
is that it won't work with our snapshot reads since coprocessors aren't invoked
in this case.
For Phoenix, the best solution would be to:
- Create a RegionScanner which is the first one in the chain that hides the
shadow cell interaction.
- Ensure the shadow cell qualifier is projected in the scan from the client
side. This can be done through a new TAL method called from
BaseResultIterators.initializeScan(). Also, somewhat unrelated, but make sure
the time range is setup correctly on the client side. Tephra does this through
a coprocessor, but it'd be fine to do it on the client side instead.
> Hide shadow cell and commit table access in TAL
> -----------------------------------------------
>
> Key: PHOENIX-4232
> URL: https://issues.apache.org/jira/browse/PHOENIX-4232
> Project: Phoenix
> Issue Type: Bug
> Reporter: James Taylor
> Labels: omid
>
> Omid needs to project the shadow cell column qualifier and then based on the
> value, filter the row. If the shadow cell is not found, it needs to perform a
> lookup in the commit table (the source of truth) to get the information
> instead. For the Phoenix integration, there are likely two TAL methods that
> can be added to handle this:
> # Add method call to new TAL method in preScannerOpen call on coprocessor
> that projects the shadow cell qualifiers and sets the time range. This is
> equivalent to the TransactionProcessor.preScannerOpen that Tephra does. It's
> possible this work could be done on the client side as well, but it's more
> likely that the stuff that Phoenix does may override this (but we could get
> it to work if need be).
> # Add TAL method that returns a RegionScanner to abstract out the filtering
> of the row (potentially querying commit table). This RegionScanner would be
> added as the first in the chain in the
> NonAggregateRegionScannerFactory.getRegionScanner() API.
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