计算机技术学习记录

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  • 追踪java 程序中的线程执行情况

    当我们希望观察java程序运行的堆栈情况,多次执行jstack,或者通过cpu 采用发现某个线程都在同一个函数函数.

    这可能是两种情况引起的:

    1. 在这个线程中,这个函数是高频函数.
    2. 线程当前阻塞在这个函数上.

    Linux中没有真正的线程,java线程是由进程来模拟实现的. 这种进程又称作:轻量级进程(LWP).

    因此可以通过strace -p 追踪其运行情况,来区分以上两种情况.

    但是通过ps -ef或者jps只能看到java程序的pid. 如果需要追踪线程,可以jstack查找线程的pid.

    线程第一个行中的 nid字段,就是该线程pid的16进制表示. 转化为10进制即可.

    例如下面,线程显示在执行io上,读数据相对这个操作是比重多的. 但是是频繁执行io,还是文件系统出现问题,卡在io上,这是无法区分. 就可以这样追踪一下.

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  • rpm 与 yum 常用查询功能

    [TOC]

    例如查询ceph rados 命令的依赖包

    ldd /usr/bin/rados |awk '{print $3}'|grep '^/' |xargs -i  rpm -qf {}|xargs -i rpm -qi {} |grep ceph -B 10 -A 10

    rpm 查询

    rpm -qf 查询文件来源于那个package

    [root@localhost ~]# rpm -qf /usr/bin/rados
ceph-common-10.2.10-0.el7.x86_64

    rpm -qi 查询rpm package 信息

    rpm -qi ceph-common
Name        : ceph-common
Epoch       : 1
Version     : 10.2.10
Release     : 0.el7
Architecture: x86_64
Install Date: Sat 23 May 2020 04:12:25 PM CST
Group       : System Environment/Base
Size        : 62321887
License     : LGPL-2.1 and CC-BY-SA-1.0 and GPL-2.0 and BSL-1.0 and GPL-2.0-with-autoconf-exception and BSD-3-Clause and MIT
Signature   : RSA/SHA1, Mon 13 Nov 2017 05:33:12 PM CST, Key ID d4a2e50be451e5b5
Source RPM  : ceph-10.2.10-0.el7.src.rpm
Build Date  : Wed 18 Oct 2017 11:04:07 PM CST
Build Host  : c1bj.rdu2.centos.org
Relocations : (not relocatable)
Packager    : CBS <cbs@centos.org>
Vendor      : CentOS
URL         : http://ceph.com/
Summary     : Ceph Common
Description :
Common utilities to mount and interact with a ceph storage cluster.
Comprised of files that are common to Ceph clients and servers.

    rpm -qR 查询package 依赖

    [root@localhost ~]# rpm -qR ceph-common
/bin/bash
/bin/sh
/bin/sh
/bin/sh
/bin/sh
/usr/bin/env
config(ceph-common) = 1:10.2.10-0.el7
ld-linux-x86-64.so.2()(64bit)
ld-linux-x86-64.so.2(GLIBC_2.3)(64bit)
libbabeltrace-ctf.so.1()(64bit)
libbabeltrace.so.1()(64bit)
libblkid.so.1()(64bit)
libblkid.so.1(BLKID_1.0)(64bit)
...

    rpm -qa 查找所以

    [root@localhost ~]# rpm -qa |grep ceph
centos-release-ceph-jewel-1.0-1.el7.centos.noarch
libcephfs1-10.2.10-0.el7.x86_64
python-cephfs-10.2.10-0.el7.x86_64
ceph-common-10.2.10-0.el7.x86_64

    rpm -q

    [root@localhost ~]# rpm -q ceph-common
ceph-common-10.2.10-0.el7.x86_64
[root@localhost ~]# rpm -q ceph-common-10.2.10-0.el7.x86_64
ceph-common-10.2.10-0.el7.x86_64
[root@localhost ~]# rpm -q ceph-common-10.2.10-0.el7
ceph-common-10.2.10-0.el7.x86_64

    yum 查询

    yum 查询软件可用版本

    [root@localhost ~]# yum list ceph-common --showduplicates
Loaded plugins: fastestmirror
Loading mirror speeds from cached hostfile
 * base: mirrors.njupt.edu.cn
 * centos-qemu-ev: mirrors.ustc.edu.cn
 * extras: mirrors.dgut.edu.cn
 * updates: mirrors.dgut.edu.cn
Installed Packages
ceph-common.x86_64      1:10.2.10-0.el7  @centos-ceph-jewel
Available Packages
ceph-common.x86_64      1:10.2.5-4.el7   base
ceph-common.x86_64      1:10.2.7-0.el7   centos-ceph-jewel
ceph-common.x86_64      1:10.2.10-0.el7  centos-ceph-jewel

    yum 查询软件需要的依赖

    [root@localhost ~]#  yum deplist ceph-common

Loaded plugins: fastestmirror
Repodata is over 2 weeks old. Install yum-cron? Or run: yum makecache fast
Loading mirror speeds from cached hostfile
 * base: mirrors.njupt.edu.cn
 * centos-qemu-ev: mirrors.ustc.edu.cn
 * extras: mirrors.dgut.edu.cn
 * updates: mirrors.dgut.edu.cn
package: ceph-common.x86_64 1:10.2.10-0.el7
  dependency: /bin/bash
   provider: bash.x86_64 4.2.46-34.el7
  dependency: /bin/sh
   provider: bash.x86_64 4.2.46-34.el7
  dependency: /usr/bin/env
   provider: coreutils.x86_64 8.22-24.el7_9.2
  dependency: ld-linux-x86-64.so.2()(64bit)
   provider: glibc.x86_64 2.17-324.el7_9
  dependency: ld-linux-x86-64.so.2(GLIBC_2.3)(64bit)
   provider: glibc.x86_64 2.17-324.el7_9

  • 笔记_CPU缓存知识

    记录一下 cpu cache 相关内容

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  • git merge,rebase,reset

    老分不清怎么用git merge 与 rebase 区别.
    撤回的时候使用git reset 又忘了具体参数.

    git log

    显示提交的详细信息

    commit 2ec3438b5c53932e928ec4284c5121acb86f2abb (HEAD -> mdfs-ng, origin/mdfs-ng)
Author: #小辉辉 <xxxx.com>
Date:   Tue Apr 17 17:30:22 2018 +0800

    clear : del unused code

    git log –pretty=oneline

    只显示commit id和提交的描述信息

    2ec3438b5c53932e928ec4284c5121acb86f2abb (HEAD -> mdfs-ng, origin/mdfs-ng) clear : del unused code
8a78c5779328d2e48826b9203a50d596d508392f update : clear code by sonar

    git reflog

    可以查看所有分支的所有操作记录.包括已经删除commit记录

    2a84922 HEAD@{158}: checkout: moving from hui-comment to devel
0d0b108 (master, hui-comment) HEAD@{159}: checkout: moving from master to hui-comment

    HEAD

    HEAD 意义
    HEAD 提交的最新版本
    HEAD^ 上一个版本
    HEAD^^ 上上个版本
    HEAD~100 往上100个版本
    HEAD@{index} 提交索引

    git reset

    git reset --hard HEAD@{2}

    git commit –amend

    修改已经提交的信息

    git rebase

    合并

    1. 合并1~3条提交 
      git rebase -i HEAD~3

pick dc44d6b 根据sonar修改FixedLenChunkFingerIndexDB
pick 8a78c57 update : clear code by sonar
pick 2ec3438 clear : del unused code

#将pick改为squash或者s,之后保存并关闭文本编辑窗口即可
pick dc44d6b 根据sonar修改FixedLenChunkFingerIndexDB
s 8a78c57 update : clear code by sonar
s 2ec3438 clear : del unused code
    2. 指名要合并的版本之前的版本号 
      git rebase -i 0d0b108
    3. 遇到冲突需要使用 
      git add .  
git rebase --continue
    4. 取消 
      git rebase --abort

    Merging vs. Rebasing

    The first thing to understand about git rebase is that it solves the same problem as git merge.

    The Merge Option

    git checkout feature
git merge master
#Or, you can condense this to a one-liner:
git merge master feature

    The Rebase Option

    git checkout feature
git rebase master

    参考

    (Git)合并多个commit

    7. 用rebase合并
    Merging vs. Rebasing

  • outline accesskey format

    ss://base64(method:passwod)@server-address:port