gaurav kadaskar created NIFI-15634:
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Summary: Full query execution during metadata discovery for
Generic/MySQL in QueryDatabaseTableRecord causes high heap usage.
Key: NIFI-15634
URL: https://issues.apache.org/jira/browse/NIFI-15634
Project: Apache NiFi
Issue Type: Bug
Affects Versions: 2.7.2
Reporter: gaurav kadaskar
h3. Problem
When Database Type is set to Generic or MySQL in QueryDatabaseTableRecord,
getDatabaseDialectService() returns DatabaseAdapterDatabaseDialectService.
During metadata discovery, NiFi executes the full user query instead of using a
metadata-only query. Since no guard condition is applied, the query scans the
entire dataset, which leads to high heap usage and JVM memory pressure for
large result sets.
h3. Previous Behavior
Earlier NiFi versions generated a metadata-safe query by appending:
{code:sql}
WHERE 1=0
{code}
This allowed schema retrieval without reading actual data.
h3. Expected Behavior
Metadata discovery should use a metadata-only query and must not execute the
full user query.
h3. Current Behavior
Full user query is executed to obtain metadata.
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