mysqltest merge_join.mj_slave_mapping: EXPLAIN does not generate baseline MERGE JOIN parallel plan, actual execution plan uses NESTED-LOOP JOIN / TABLE GET path

Environment

• Platform: Android (arm64)
• Device: Android Studio emulator (emulator-5554)
• Binary: ./data/local/tmp/seekdb
• Startup Command: ./data/local/tmp/seekdb --nodaemon --base-dir /data/local/tmp/seekdb_data --port 5881
• Port: 5881

Description

In the merge_join.mj_slave_mapping mysqltest, the EXPLAIN output does not generate the parallel plan based on MERGE JOIN that is stored in the baseline. Instead, the actual execution plan follows a NESTED-LOOP JOIN / TABLE GET path.

Steps to Reproduce

1. Access the test machine.
2. Execute the relevant steps for the merge_join.mj_slave_mapping test case.
3. Observe the discrepancy between the plan shown by EXPLAIN (which should reflect the baseline's MERGE JOIN parallel plan) and the actual execution plan used.

Actual Result

The actual execution path deviates from the expected baseline, utilizing NESTED-LOOP JOIN and TABLE GET operations instead of the intended MERGE JOIN parallel plan.

Start by running the mysqltest case merge_join.mj_slave_mapping in the provided seekdb Android environment and compare its EXPLAIN output with the stored baseline. Trace the discrepancy between the expected parallel MERGE JOIN plan and the observed NESTED-LOOP JOIN / TABLE GET path; done means the test's EXPLAIN and actual execution plan match the intended baseline.