Fix JDBC hasChildren fetching all rows and columns#5066
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Pull request overview
This PR optimizes JdbcBasePersistenceImpl.hasChildren in the relational JDBC persistence layer to avoid selecting wide entity rows (including large JSON blob columns) when only row existence is needed.
Changes:
- Add
QueryGenerator.generateExistsQuery(...)to emitSELECT 1 ... LIMIT 1existence checks. - Update
JdbcBasePersistenceImpl.hasChildrento use the new existence query instead of a full entity-columnSELECT. - Add/extend tests to verify
LIMIT 1usage and thatproperties/internal_propertiesare not fetched.
Reviewed changes
Copilot reviewed 4 out of 4 changed files in this pull request and generated 1 comment.
| File | Description |
|---|---|
| persistence/relational-jdbc/src/main/java/org/apache/polaris/persistence/relational/jdbc/QueryGenerator.java | Adds an existence-query generator (SELECT 1 ... LIMIT 1). |
| persistence/relational-jdbc/src/main/java/org/apache/polaris/persistence/relational/jdbc/JdbcBasePersistenceImpl.java | Switches hasChildren to the existence-query path to avoid fetching wide rows. |
| persistence/relational-jdbc/src/test/java/org/apache/polaris/persistence/relational/jdbc/QueryGeneratorTest.java | Adds assertions ensuring the existence query uses SELECT 1 + LIMIT 1 and avoids blob columns. |
| persistence/relational-jdbc/src/test/java/org/apache/polaris/persistence/relational/jdbc/JdbcBasePersistenceImplTest.java | Adds an integration-style test validating hasChildren issues a limited existence query (no blob columns). |
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| public static PreparedQuery generateExistsQuery( | ||
| @NonNull String tableName, @NonNull Map<String, Object> whereClause) { | ||
| QueryFragment where = generateWhereClause(whereClause.keySet(), whereClause, Map.of()); | ||
| String sql = | ||
| "SELECT 1 FROM " + getFullyQualifiedTableName(tableName) + where.sql() + " LIMIT 1"; | ||
| return new PreparedQuery(sql, where.parameters()); |
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hmm, as of now it had one caller only, but fair enough, I have changed it & added a test as well around it
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adutra
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Jul 17, 2026
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@ayushtkn could you please fix the merge conflict? Thanks! |
adutra
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Jul 17, 2026
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JdbcBasePersistenceImpl.hasChildrenwas issuing aSELECTof all15+entity columns—including large JSONpropertiesandinternal_propertiesblobs—with noLIMIT, just to answer whether any children exist.Checklist
CHANGELOG.md(if needed)site/content/in-dev/unreleased(if needed)