Huge strings in auth_saml2_kvstore killing binlogs

[thepurpleblob]

We're seeing lots of instances of SAML2 writing huge strings into the above table. This is really giving our MySQL binlogs a hard time.

For example,

mysql> SELECT id,CHAR_LENGTH(value) AS LengthOfValue FROM mdl_auth_saml2_kvstore WHERE type ='session' AND expire LIKE '%17128%' ORDER BY LengthOfValue DESC LIMIT 50;
+----------+---------------+
| id | LengthOfValue |
+----------+---------------+
| 86592929 | 11746895 |
| 86667038 | 2940322 |
| 86693668 | 491520 |
| 86690961 | 452214 |
| 86671596 | 370979 |
| 86657364 | 365110 |
| 86667991 | 332414 |
| 86682949 | 309809 |
| 86661475 | 302619 |
| 86693929 | 266779 |
| 86542932 | 208408 |
| 86656869 | 142746 |
| 86639173 | 136263 |
| 86693906 | 122913 |
| 86672287 | 113278 |
| 86678033 | 93596 |
| 86661860 | 89038 |
| 86666163 | 81738 |
| 86667252 | 74356 |
| 86692985 | 65551 |
| 86653795 | 62838 |
| 86668024 | 53938 |
| 86700326 | 52604 |
| 86699423 | 44089 |
| 86676443 | 43073 |
| 86697650 | 42877 |
| 86698672 | 42843 |
| 86658119 | 41643 |
| 86697902 | 41274 |
| 86684273 | 37895 |
| 86694783 | 37530 |
| 86671134 | 35639 |
| 86692707 | 33447 |
| 86698889 | 33435 |
| 86685503 | 33213 |
| 86698780 | 33030 |
| 86676098 | 32862 |
| 86689231 | 32438 |
| 86697899 | 31828 |
| 86653773 | 31770 |
| 86676007 | 31592 |
| 86692234 | 31261 |
| 86672538 | 30002 |
| 86700580 | 29471 |
| 86666900 | 29337 |
| 86693485 | 29227 |
| 86678194 | 28523 |
| 86700589 | 26585 |
| 86691036 | 25049 |
| 86687700 | 24703 |
+----------+---------------+
50 rows in set (0.55 sec)

I'm not sure if this is expected / unexpected and what to do next. Any help appreciated?

[ph25sl]

The timing of your post is so coincidental as I've just spent time investigating the same too.

[ph25sl]

Possibly a duplicate of this closed issue or at least related to #458