[
https://issues.apache.org/jira/browse/KUDU-3782?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel
]
Gabriella Lotz reassigned KUDU-3782:
------------------------------------
Assignee: Gabriella Lotz
> TServer aborts (SIGABRT / std::length_error) on COUNT(*) scans with predicates
> ------------------------------------------------------------------------------
>
> Key: KUDU-3782
> URL: https://issues.apache.org/jira/browse/KUDU-3782
> Project: Kudu
> Issue Type: Bug
> Components: tserver
> Reporter: Gabriella Lotz
> Assignee: Gabriella Lotz
> Priority: Critical
>
> h3. Summary
> When a tablet server serves a counting scan
> {noformat}
> COUNT(*) or COUNT(<constant>), {noformat}
> that also carries column predicates, MaterializingIterator::Init (in
> src/kudu/common/generic_iterators.cc) computes the number of projected
> columns minus the number of predicates using mismatched signed/unsigned
> types. When the projected column count is smaller than the predicate count,
> the subtraction underflows to a very large value, which is passed to
> std::vector::reserve, throwing an uncaught std::length_error and aborting the
> process.
>
> This happens because the projection for a counting scan is tiny, while during
> initialization the rowset iterator (CFileSet::Iterator::OptimizePKPredicates
> → LiftPrimaryKeyBounds) re-adds predicates derived from the rowset's primary
> key bounds on key columns that are not in the projection. The guarding
> DCHECK_GE is compiled out in release builds, so release builds reach the
> underflow. It is intermittent because it depends on the rowset's on-disk key
> layout.
> Trigger: a
> {code:java}
> COUNT(*)/COUNT(<const>){code}
> query with predicates on a non-contiguous subset of a composite primary key,
> against a rowset whose primary key bounds share a long constant prefix.
> h3. Fix (in MaterializingIterator::Init)
> Remove the invalid DCHECK_GE, compute the reservation so it cannot underflow,
> and skip predicates whose column is not in the projection (these are
> rowset-derived and already enforced by the key range) instead of failing the
> scan. A regression test covering a projection smaller than the predicate set
> passes with this change, and the existing generic_iterators-test suite
> continues to pass.
> h3. Workaround
> Rewrite affected counting queries so the scan projects real columns, for
> example by wrapping the count in a sub-query that selects actual rows. A
> non-empty projection avoids the code path entirely. Only COUNT(...) queries
> that include a WHERE clause can trigger this.
--
This message was sent by Atlassian Jira
(v8.20.10#820010)
