MySQL Bugs: #42484: Falcon temporary data inconsistency with LIMIT

Bug #42484	Falcon temporary data inconsistency with LIMIT
Submitted:	30 Jan 16:19	Modified:	30 Jan 16:24
Reporter:	Philip Stoev
Status:	Verified
Category:	Server: Falcon	Severity:	S2 (Serious)
Version:	6.0-falcon-team	OS:	Any
Assigned to:	Kevin Lewis	Target Version:	6.0-beta
Tags:	ISOLATION, F_LIMIT
Triage:	Triaged: D2 (Serious)

Description:
When executing a non-concurrent workload containing simple UPDATES on a key, SELECT
statements will temporarily return different results when executed with and without the
Falcon LIMIT optimization.

The failure is temporary and the table remains consistent in the long term. No range
scans or NULLS are involved.

How to repeat:
A test case will be uploaded shortly.

ZZ file for bug 42484

Attachment: bug42484.zz (text/plain), 336 bytes.

YY file for bug 42484

Attachment: bug42484.yy (application/octet-stream, text), 177 bytes.

To reproduce:

$ runall.pl \
 --basedir=/build/bzr/6.0-falcon-team \
 --mysqld=--loose-innodb-lock-wait-timeout=1 \
 --mysqld=--table-lock-wait-timeout=1 \
 --mysqld=--loose-falcon-lock-wait-timeout=1 \
 --mysqld=--loose-falcon-debug-mask=2 \
 --mysqld=--skip-safemalloc \
 --grammar=bug42484.yy \
 --gendata=bug42484.zz \
 --threads=1 \
 --validator=Limit \
 --duration=1200 \
 --mysqld=--log-output=file \
 --queries=100000 \
 --engine=falcon

This test will fail immediately after takeoff, reporting the query that returns the
inconsistent result. Re-executing the query manually shows that the inconsistency was
transient. 10 inserts and 11 updates, all prerfectly valid queries.