Category Archives: develope

Use type of “Any” carefully in Scala

Think about the code below:

I intent to see the compiler error for second ‘increment’ int the first place. But it don’t, the compiler report ok and the output of the program is:

The compiler recognize the three arguments “world”, “6”, “7” as a tuple of (“world”, 6,… Read more »

Usage limitations of HDFS’s C API

I have to change a program which is written by c language from writing local files to writing on HDFS. After learning the example of C API in libhdfs, I complete the modification of open()/write()/read() to hdfsOpenFile()/hdfsWriteFile()/hdfsReadFile() and so on. But when running the new program, many problems occured. The… Read more »

Network problem of installing docker-engine on Centos-7

After installing docker-engine on Centos-7, it failed to start by

After I use

it shows:

To see more details, I use

There were much more informations now:

The ethernet interface of docker0 can not be assigned IPv4 addresse. It seems many people meet this problem… Read more »

The CPU usage of soft-irq will be counted into a process.

Redis usually runs as a single process daemon that is the perfect sample of UNIX philosophy — one process just do one thing. But current servers have many CPUs(Cores) so we need to launch many Redis processes to provide service. After running multi-process redis-server in server, I found out there… Read more »

Avoid “page allocation failure” for linux kernel in big memory server

After adding pressure to a Key-Value cluster, I found many error in dmesg:

It’s hard to understand the “page allocation failure” error because the memory capacity is very big in our servers. By looking at the result “free” command, I noticed that a large mount of memory was used… Read more »

Too many “ext4-dio-unwrit” processes in system

After adding pressure to application which will write tremendous data into ext4 file system, we see many “ext4-dio-unwrit” kernel threads in “top” screen. Many guys say this is a normal phenomenon, so I check the source code of ext4 in 2.6.32 linux kernel. The beginning of writing a file in… Read more »

Why you should update your gcc (and c++ library)

Consider the code below:

It could be compiled and run on CentOS 5 (gcc-4.1.2), but will core dump at runtime.

The gdb stack shows the breakpoint is in string_hashfunc::operator():

Let’s see the source code of “ext/hash_map” in /usr/include/c++/4.1.2/ext/hashtable.h:

And in the implementation of _M_bkt_num():

It… Read more »

Why you should update your gcc

Consider this c++ code:

I compiled it on CentOS-5 on which the version of gcc is 4.1.2 in the first place and it report:

Can anyone find out the problem at first glance of this mess report ? The error report of c++ template is terrible difficult to… Read more »

Upgrade to kernel-4.4.1 on CentOS 7

After I compiled and installed kernel-4.4.1 (from 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… Read more »