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GET_LOCK in ndb clusters
Posted by: Pete Ditmars
Date: October 19, 2021 08:23AM

Hi,

Can someone confirm whether GET_LOCK() can be made to work cluster-wide across an NDB cluster?

If it can be made to work, what is the configuration setting is that we are missing, because I just confirmed I can lock the same name multiple times from different sessions with GET_LOCK() when connecting to different mysqld servers.

I can't believe I assumed this would work... and am now finding it doesn't.

The documentation in section 12.15 "Locking Functions" here https://dev.mysql.com/doc/refman/5.7/en/locking-functions.html

says innocently enough (after many paragraphs explaining how it works)

"Names are locked on a server-wide basis"

Is implicit in that comment that "Names are NOT locked on an NDB cluster-wide basis. The same name can be locked by different sessions if they connect to different mysql servers within a single cluster." ?

I'm looking in section 23.2.7 Known Limitations of NDB Cluster here https://dev.mysql.com/doc/refman/8.0/en/mysql-cluster-limitations.html
and I don't see GET_LOCK listed anywhere.

I see in section 23.2.7.10 Limitations Relating to Multiple NDB Cluster Nodes
https://dev.mysql.com/doc/refman/8.0/en/mysql-cluster-limitations-multiple-nodes.html
that "No distributed table locks" is a limitation but GET_LOCK is not mentioned.

Thanks for any help, or even confirmation that this doesn't work.

Pete

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