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https://issues.apache.org/jira/browse/CASSANDRA-19795?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel
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Nadav Har'El updated CASSANDRA-19795:
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Description:
As explained many years ago in
https://issues.apache.org/jira/browse/CASSANDRA-5470, when a query involves
intersecting two secondary indexes, e.g., "WHERE x=1 AND y=2" where "x" and "y"
are two indexed column, ALLOW FILTERING is required.
I verified that this is still the case today, in Cassandra 5.0-rc1. If you use
SAI instead of the classic secondary index, suddenly ALLOW FILTERING is not
required.
I think this is a regression. Even if SAI has a more efficient way of
intersecting the posting list from two indexes (does it?), in the worst case
this doesn't help: For example, consider a table with a million rows, half have
x=1 and the other half have y=2 and just one row has both. Now, a query for
"WHERE x=1 AND y=2" needs to process half a million rows just to produce one
result. This is ALLOW FILTERING par excellence.
was:
As explained many years ago in
https://issues.apache.org/jira/browse/CASSANDRA-5470, when a query involves
intersecting two secondary indexes, e.g., "WHERE x=1 AND y=2" where "x" and "y"
are two indexed column, ALLOW FILTERING is required.
I verified that this is still the case today, in Cassandra 5.0-rc1, but ALLOW
FILTERING is suddenly not required for this query if you use SAI instead of the
classic secondary index.
I think this is a regression. Even if SAI has a more efficient way of
intersecting the posting list from two indexes (does it?), in the worst case
this doesn't help: For example, consider a table with a million rows, half have
x=1 and the other half have y=2 and just one row has both. Now, a query for
"WHERE x=1 AND y=2" needs to process half a million rows just to produce one
result. This is ALLOW FILTERING par excellence.
> In SAI, intersecting two indexes doesn't require ALLOW FILTERING
> ----------------------------------------------------------------
>
> Key: CASSANDRA-19795
> URL: https://issues.apache.org/jira/browse/CASSANDRA-19795
> Project: Cassandra
> Issue Type: Bug
> Components: Feature/2i Index
> Reporter: Nadav Har'El
> Priority: Normal
>
> As explained many years ago in
> https://issues.apache.org/jira/browse/CASSANDRA-5470, when a query involves
> intersecting two secondary indexes, e.g., "WHERE x=1 AND y=2" where "x" and
> "y" are two indexed column, ALLOW FILTERING is required.
> I verified that this is still the case today, in Cassandra 5.0-rc1. If you
> use SAI instead of the classic secondary index, suddenly ALLOW FILTERING is
> not required.
> I think this is a regression. Even if SAI has a more efficient way of
> intersecting the posting list from two indexes (does it?), in the worst case
> this doesn't help: For example, consider a table with a million rows, half
> have x=1 and the other half have y=2 and just one row has both. Now, a query
> for "WHERE x=1 AND y=2" needs to process half a million rows just to produce
> one result. This is ALLOW FILTERING par excellence.
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