hadoop commands tutorial

query time, resulting in slower efficiency. The workaround is to use the index for sorting. If the order required for the query is the same as the sort used by the index, because the indexes are sorted, and therefore the results are returned in sequential read by index, the using Filesort does not appear at this time.As for the difference between using index and using index condition, I refer to an article on StackOverflowHttp://stackoverflow.com/questions/1687548/mysql-explain-using-index-vs-u

the query, and Usingfilesort will appear. Sorting naturally increases query time, resulting in slower efficiency. The workaround is to use the index for sorting. If the order required for the query is the same as the sort used by the index, because the indexes are sorted, and therefore the results are returned in sequential read by index, the using Filesort does not appear at this time. As for the difference between using index and using index condition, I refer to an article on StackOverflow H

First, view the text:Cat: Connect and Show TAC: Reverse display of text content-N: Show line numbers-E: Displays the line terminator for each lineNote: For Linux systems, the line terminator for each line of the text file is $. The Windows system has two terminator: $ and line breaks.Second, split screen display:MORE: Only support backward, turn to the last screen exit.Less: Same as manSPACE:B:ENTER:K:Third, head, tailHead-n View Top N rowsTail-n: View after n rows-F: Look at the end of the file

time-I: Inactive time-M: Minimum period of use-M: Maximum lifespan-W: Warning timePractice: Create a user Mandriva with an ID number of 2002, a base group of distro (group ID 3003), and an additional group of Linux #:groupadd-g 3003 distro#:groupadd Linux#:useradd-u 2002-g distro-g Linux Mandriva2. Create a user fedora with the full name of Fedora Community, the default shell is tcsh#:useradd-c "Fedora Community"-s/bin/tcsh Fedora3. Modify Mandriva with ID 4004, Basic Group Linux,

1.chmod (Rights Management) [[email protected] tem]# chmod-r 777/tem/a/b recursive change of permissions;Permission number method owner, root to change permissions;R----4W---2X---12.chown change the file or owner;[email protected] tem]# Touch Fengjie[Email protected] tem]# ls-l Fengjie-rw-r--r--. 1 root root 0 April 11:42 Fengjie[Email protected] tem]# Useradd Shenchao[Email protected] tem]#[Email protected] tem]# chown Shenchao Fengjie[Email protected] tem]# ls-l Fengjie-rw-r--r--. 1 shenchao R