https://bugzilla.wikimedia.org/show_bug.cgi?id=69182
Bug ID: 69182
Summary: Database upgrade MariaDB 10: Metadata access in
INFORMATION_SCHEMA causes complete blocks
Product: Wikimedia Labs
Version: unspecified
Hardware: All
OS: All
Status: UNCONFIRMED
Severity: critical
Priority: Unprioritized
Component: Infrastructure
Assignee: [email protected]
Reporter: [email protected]
CC: [email protected], [email protected],
[email protected], [email protected]
Web browser: ---
Mobile Platform: ---
When accessing INFORMATION_SCHEMA, query hangs up on random schemas and causes
a widespread block for that server/listener.
- This occurs especially when accessing INFORMATION_SCHEMA through listener
s2/s4/s5.labsdb (192.168.99.12). No timeout.
- This occures also when accessing INFORMATION_SCHEMA through listener
s1.labsdb (192.168.99.1), but here with kill/timout of 16 sec.
-both: kill clean-ups take up to 500 sec.
- This does not occur when accessing INFORMATION_SCHEMA through listener
s3.labsdb (192.168.99.3) - still old DB.
Currently, access to INFORMATION_SCHEMA on new Servers is basically very slow.
A simple query takes up to 3 sec (if it doesn't hang up). As (console)-clients
do auto-rehashing on connect (unless it's turned off), they hang, too.
Maybe it's realted to spinning-rust, but this doesn't explain the difference
between s1 and eg. s5. - and it shouldn't hang up at all, even if running slow.
Is there something like innodb_stats_on_metadata enabled for tokuDB? Or are
some schemas kind of broken?
References:
http://tools.wmflabs.org/tools-info/misc/schema-block-hang.png
http://tools.wmflabs.org/tools-info/misc/schema-block-cleanup.png
Simple Metadata-query:
SELECT table_schema, data_length, index_length
FROM INFORMATION_SCHEMA.TABLES
WHERE table_schema = '<some_schema>'
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