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https://issues.apache.org/jira/browse/PHOENIX-2606?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel
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Sudarshan Kadambi updated PHOENIX-2606:
---------------------------------------
Description:
Phoenix should look to support a cursor model where the user could set the
fetch size to limit the number of rows that are fetched in each batch. Each
batch of result rows would be accompanied by a flag indicating if there are
more rows to be fetched for a given query or not.
The state management for the cursor could be done in the client side or server
side (i.e. HBase, not the Query Server). The client side state management could
involve capturing the last key in the batch and using that as the start key for
the subsequent scan operation. The downside of this model is that if there were
any intervening inserts or deletes in the result set of the query, backtracking
on the cursor would reflect these additional rows (consider a page down,
followed by a page up showing a different set of result rows). Similarly, if
the cursor is defined over the results of a join or an aggregation, these
operations would need to be performed again when the next batch of result rows
are to be fetched.
So an alternate approach could be to manage the state server side, wherein
there is a query context area in the Regionservers (or, maybe just a temporary
table) and the cursor results are fetched from there. This ensures that the
cursor has snapshot isolation semantics. I think both models make sense but it
might make sense to start with the state management completely on the client
side.
was:
Phoenix should look to support a cursor model where the user could set the
fetch size to limit the number of rows that are fetched in each batch. Each
batch of result rows would be accompanied by a flag indicating if there are
more rows to be fetched for a given query or not.
The state management for the cursor could be done in the client side or server
side (i.e. HBase, not the Query Server). The client side state management could
involve capturing the last key in the batch and using that as the start key for
the subsequent scan operation. The downside of this model is that if there were
any intervening inserts or deletes in the result set of the query, backtracking
on the cursor would reflect these additional rows (consider a page down,
followed by a page up showing a different set of result rows). Similarly, if
the cursor is defined over the results of a join or an aggregation, these
operations would need to be performed again when the next batch of result rows
are to be fetched. So an alternate approach could be to manage the state server
side, wherein there is a query context area in the Regionservers (or, maybe
just a temporary table) and the cursor results are fetched from there. This
ensures that the cursor has snapshot isolation semantics. I think both models
make sense but it might make sense to start with the state management
completely on the client side.
> Cursor support in Phoenix
> -------------------------
>
> Key: PHOENIX-2606
> URL: https://issues.apache.org/jira/browse/PHOENIX-2606
> Project: Phoenix
> Issue Type: New Feature
> Reporter: Sudarshan Kadambi
>
> Phoenix should look to support a cursor model where the user could set the
> fetch size to limit the number of rows that are fetched in each batch. Each
> batch of result rows would be accompanied by a flag indicating if there are
> more rows to be fetched for a given query or not.
> The state management for the cursor could be done in the client side or
> server side (i.e. HBase, not the Query Server). The client side state
> management could involve capturing the last key in the batch and using that
> as the start key for the subsequent scan operation. The downside of this
> model is that if there were any intervening inserts or deletes in the result
> set of the query, backtracking on the cursor would reflect these additional
> rows (consider a page down, followed by a page up showing a different set of
> result rows). Similarly, if the cursor is defined over the results of a join
> or an aggregation, these operations would need to be performed again when the
> next batch of result rows are to be fetched.
> So an alternate approach could be to manage the state server side, wherein
> there is a query context area in the Regionservers (or, maybe just a
> temporary table) and the cursor results are fetched from there. This ensures
> that the cursor has snapshot isolation semantics. I think both models make
> sense but it might make sense to start with the state management completely
> on the client side.
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