Performance bottleneck in Jedis

I have had write a test program which using Jedis to read/write Redis Cluster. It create 32 threads and every thread init a instance of JedisCLuster(). But it will cost more than half minute to create total 32 JedisCluster Instances.
By tracking the problem, I found out that the bottleneck is in setNodeIfNotExist():

In the method setNodeIfNotExist() of class JedisClusterInfoCache, “new JedisPool()” will cost a lot of time because it will use apache commons pool and apache-commons-pool will register MBean Server with JMX. The register operation of JMX is the bottelneck.

The first solution for this problem is to disable JMX when calling JedisCluster():

The second solution is “create one JedisCluster() instance for all threads”. After I commited patch for Jedis to set JMX disable as default, Marcos Nils remind me that JedisCluster() is thread-safe, for it has using commons-pool to manage the connection resource.

Upgrade to kernel-4.4.1 on CentOS 7

After I compiled and installed kernel-4.4.1 (from kernel.org) on my CentOS 7, I reboot the machine. But it can’t boot up correctly.
Using

to extract the content in initramfs and check them, I found out the ‘mpt2sas’ kernel driver had not been added into initramfs so /boot partition could not be loaded.

Seems this problem is common. Because changing dracut source code or configure file on all servers is not viable, I chose to add command in my kernel rpm spec file:

This will add drivers to the corresponding initramfs file.

But the kernel could not boot up either. This time, I found that the command line in GRUB2 is like:

Looks we should change it to UUID. Add another command in kernel rpm spec file:

This will get UUID of boot disk from /proc/cmdline and give it to GRUB2 configure file.

Now, the kernel-4.4.1 boot up correctly on CentOS 7.

The importance of Declaration in c language

Let’s create two c language files,

and compile & link them:

But after run “./test”, the result is

Why the result from myNumber() become different in main() function?

Let’s see the assembly language source of test.c (gcc -S test.c)

It only get the 32-bits result from function ‘myNumber’ (The size of %eax register is just 32-bits, smaller than the size of “long long”). Actually, we missed the declaration of myNumber() in test.c file so it only consider the result of myNumber() as 32-bits size.
After adding the declaration of myNumber() into test.c, we could check the assembly language source has changed:

(The size of %rax register is 64-bits)
And the result of running ‘./test’ is correct now.