shubhluck opened a new pull request, #6382:
URL: https://github.com/apache/hive/pull/6382
…re unavailable
Added null checks before iterating over column statistics in:
- StatsUtils.updateStats()
- StatsUtils.getColStatisticsUpdatingTableAlias()
- StatsRulesProcFactory (JOIN statistics) This prevents query compilation
failures during semijoin optimization when column-level statistics are
incomplete, commonly seen with large TPC-DS datasets (100GB+).
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### What changes were proposed in this pull request?
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This PR adds null checks before iterating over column statistics in three
locations to prevent NullPointerException:
1. **StatsUtils.updateStats()** - Added null check for
`stats.getColumnStats()` before the for-each loop, defaulting to empty list
when null
2. **StatsUtils.getColStatisticsUpdatingTableAlias()** - Added null check
with early return of empty list when parent column stats are null
3. **StatsRulesProcFactory** (JOIN statistics computation) - Added null
check before iterating over column stats during join statistics calculation
The root cause is that `Statistics.getColumnStats()` returns `null` (not an
empty list) when no column statistics are available:
```java
public List<ColStatistics> getColumnStats() {
if (columnStats != null) {
return Lists.newArrayList(columnStats.values());
}
return null; // Returns null, causing NPE in for-each loops
}
```
### Why are the changes needed?
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1. If you propose a new API, clarify the use case for a new API.
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Query compilation fails with NullPointerException during semijoin
optimization when column statistics are unavailable:
```
java.lang.NullPointerException
at
org.apache.hadoop.hive.ql.stats.StatsUtils.updateStats(StatsUtils.java:2067)
at
org.apache.hadoop.hive.ql.parse.TezCompiler.removeSemijoinOptimizationByBenefit(TezCompiler.java:1982)
at
org.apache.hadoop.hive.ql.parse.TezCompiler.semijoinRemovalBasedTransformations(TezCompiler.java:539)
at
org.apache.hadoop.hive.ql.parse.TezCompiler.optimizeOperatorPlan(TezCompiler.java:238)
...
```
This issue is particularly prevalent with:
Large TPC-DS datasets (100GB+) where statistics collection may be incomplete
Tables where column-level statistics have not been computed
Complex queries where intermediate operators lack column statistics
The fix ensures graceful handling when column statistics are unavailable,
allowing the optimizer to continue using row-based statistics instead of
failing.
### Does this PR introduce _any_ user-facing change?
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No. This is a bug fix that prevents query compilation failures. Previously
failing queries will now compile and execute successfully. There is no change
to query results or behavior for queries that were already working.
### How was this patch tested?
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1. Reproduced the issue with TPC-DS queries at 100GB scale where column
statistics were incomplete
2. Verified that queries failing with NPE now compile and execute
successfully after the fix
3. Verified that queries with complete column statistics continue to work
correctly and produce the same results
4. Existing unit tests pass without modification
To reproduce the original issue:
1. Generate TPC-DS dataset at 100GB+ scale
2. Do not compute column statistics (or ensure they are incomplete)
3. Run queries involving semijoin optimizations
4. Observe NPE during compilation
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