[MDEV-26026] Hang after setting show_explain_probe_join_exec_end and SET (no hang for same query without SET) Created: 2021-06-28  Updated: 2022-05-28  Resolved: 2021-07-17

Status: Closed
Project: MariaDB Server
Component/s: Optimizer, Tests
Affects Version/s: 10.2, 10.3, 10.4, 10.5, 10.6
Fix Version/s: N/A

Type: Bug Priority: Minor
Reporter: Roel Van de Paar Assignee: Roel Van de Paar
Resolution: Not a Bug Votes: 0
Labels: hang


 Description   

psergei hi! Not sure if this is a bug, though it looks to be. If not, please close.

CREATE TABLE t (c INT);
 
INSERT INTO t VALUES (1);  # Optional
 
SET @show_explain_probe_select_id=2;
 
SET debug_dbug='+d,show_explain_probe_join_exec_end';
 
SELECT c FROM t;

Will not fail/simply result in "1" output.

However,

CREATE TABLE t (c INT);
 
INSERT INTO t VALUES (1);  # Optional
 
SET @show_explain_probe_select_id=2;
 
SET debug_dbug='+d,show_explain_probe_join_exec_end';
 
SET @hang=(SELECT c FROM t);

Will hang on 10.2, 10.3, 10.4, 10.5, 10.6 debug.

It may be a shortcoming in the debug parameter, or it may be a bug in SET handling.

 Comments   
Comment by Sergei Golubchik [ 2021-06-28 ]

Roel, if your bug report involves debug_dbug or, for example, randomly swapping bytes in /proc/<pid>/mem, you need to prove that the effect is really result of a bug, and not the expected outcome.

So here, you need to explain first, why this hang is a bug.

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