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Temporary Disk I/O Stalls; LCP Frag Watchdog : No progress on Table (Doc ID 1582813.1)

Last updated on DECEMBER 18, 2017

Applies to:

MySQL Cluster - Version 6.3 and later
Generic Linux


During periods with high load, for example while creating backups or executing bulk updates particularly if these involve large BLOBs, disk I/O activities are temporary stalling.

For performance critical I/O activities this may cause temporary errors and/or the data node to crash. Examples of performance critical I/O in MySQL Cluster are:


One sign of the issue - although not necessarily required - is 100% disk utilisation while nothing is written to or read from the disk, for example:

Device:         rrqm/s   wrqm/s   r/s   w/s   rsec/s   wsec/s avgrq-sz avgqu-sz   await  svctm  %util
 sda1              0.00     0.00  0.00  0.00     0.00     0.00     0.00     5.01    0.00   0.00 100.20


This describes one aspect of the issue. Other symptoms can be missed heartbeats and short stalls. It may also not always be possible to see the above disk utilisation.



The more memory that is available on the server, the more likely this issue is to happen, so the issue may begin after installing more memory or upgrading to a new server with more memory available.


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