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Xen + mysql = high load average with a low CPU load?

Development | Databases
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Good day, I have a problem - there is a machine(2x Intel Xeon E5410 + 8 gb ram) on Debian 6(x86_64) + Xen 4.It runs domU(6 cores and 3 GB of RAM, with a database of about 5 GB).Initially, this VDS had 4 cores and 2 GB of RAM, but I noticed a strange thing - the processors are evenly loaded by about 30-40%, the Load average comes to 20, mysql slows down, the programmer is indignant.The situation was saved by restarting mysql, because while the base for itself was peeling, it was not scary.It seemed to me that the processors are not enough, I added 2 more cores and 1 GB of RAM, up to 6 cores and 3 GB of RAM.LA can now reach 30, mysql again slows down.However, the processor load is lower, around 15-20%.Poked the top - the problem is not in the disk, not in the processors, not even in the RAM.The high value of the% st column confused, which reaches 85%.Actually - how to interpret% st correctly, and how to deal with such a problem, when LA is high and the processors are not really loaded?
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So, I solved the problem.Who cares - I will describe.In general, top and atop on the host machine(dom0) showed 99-100% idle cpu, the disk was used by 5%.Inside VDS(domU) wild brakes.They told me the link - CreditScheduler.xm sched-credit gave me a weight of 86(86% of 1 core).Those.6 virtual cores accounted for less than 1 physical.Fixed it through xm sched-credit -d database -c 0, where database is the name of the vsky.I asked 600, the percentages are loaded evenly.top in dom0 still reports that the host machine is not loaded, but the joke is that the top is lying - the load is noticeable through the console brakes are small and through the xentop, which shows how much CPU time each eats.Well, there is a small optimization of a couple of bold queries - now requests are executed several times faster in VDS, and there are 6 fair cores that are executed on 6 real cores, not 0.86 of one core.
on January 07th, 2020 (12:57 pm)
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