MYSQL Replication - Features and Issue

Please make sure read Replication Features and Issues before do replication

Few problem i found / concern i raise when I make replication
1 UUID in master different from slave and it do not pop any error message.

This confirm by refer to Replication and System Functions

work around solution example:
SET @my_uuid = UUID();
INSERT INTO t VALUES(@my_uuid);

quote : The USER(), CURRENT_USER(), UUID(), VERSION(), and LOAD_FILE() functions are replicated without change and thus do not work reliably on the slave.

2. Will now()function replicate correctly from master to slave? or it will generate a new date when insert data into slave?

Quote:
For NOW(), the binary log includes the timestamp. This means that the value as returned by the call to this function on the master is replicated to the slave.

Need take note this statement as well
Quote:
This can lead to a possibly unexpected result when replicating between MySQL servers in different time zones. For example, suppose that the master is located in New York, the slave is located in Stockholm, and both servers are using local time.

more refer to this link

This statement make my attention :
1. Replication of LIMIT clauses in DELETE, UPDATE, and INSERT ... SELECT statements are not guaranteed, since the order of the rows affected is not defined. Such statements can be replicated correctly only if they also contain an ORDER BY clause.

2. Replication During a Master Crash
Setting sync_binlog=1 in the master my.cnf to prevent slave not to be able to replicate when the master comes back up from crash
more detail read here

3. query with nondeterministic
It is possible for the data on the master and slave to become different if a statement is designed in such a way that the data modification is nondeterministic
Examples of nondeterministic statements include DELETE or UPDATE statements that use LIMIT with no ORDER BY clause
Reference : Replication and the Query Optimizer

Repair MYISAM table

1. online
Check table tablename
repair table tablename

2. offline
- Check all myisam table in particular database
shell> myisamchk *.MYI

- Check all myisma table in all database
shell> myisamchk /path/to/datadir/*/*.MYI

- Check and repair all myisam table
If you want to check all MyISAM tables and repair any that are corrupted, you can use the following command:

shell> myisamchk --silent --force --fast --update-state \
--key_buffer_size=64M --sort_buffer_size=64M \
--read_buffer_size=1M --write_buffer_size=1M \
/path/to/datadir/*/*.MYI


Reference
myisamchk — MyISAM Table-Maintenance Utility
Checking Tables with mysqlcheck and myisamchk
How to Repair Tables

"MySQL server has gone away" using mysqlhotcopy

"MySQL server has gone away" using mysqlhotcopy

I add the below statement in my.cnf

[mysqlhotcopy]
interactive-timeout

and mysqlhotcopy successful

show processlist and kill thread

If user not root user and no grant necessary permission,
They only allow seeing their thread when they issue "show processlist"

In order to see all threads in the server, they need "process privilege"
Logon as root and issue the below statement:
grant process on *.* to 'someone'@'%';
flush privileges;

Logon as “someone and issue the below statement:
show processlist;
All threads in mysql server will show.

We try kill one of the thread which no belong to "someone" with issue the below statement:
kill 95;
mysql give this error : You are not owner of Thread 95

If we want "someone" to kill other thread

We need to grant "super privileges"
Logon as root and issue the below statement
grant super on *.* to 'someone'@'%';
flush privileges;

Open the new connection, logon as “someone” and issue the below statement:
show processlist;
All threads in the server will be shows.
Issue the below statement to kill thread which no belong to “someone”
kill 95;
Thread Id 95 successful kill.

Notes:
- The PROCESS privilege can be used to view the plain text of currently executing statements, including statements that set or change passwords.

- The SUPER privilege can be used to terminate other sessions or change how the server operates.

- The SUPER privilege enables an account to use CHANGE MASTER TO, KILL or mysqladmin kill to kill threads belonging to other accounts (you can always kill your own threads), PURGE BINARY LOGS, configuration changes via SET GLOBAL to modify global system variables, the mysqladmin debug command, enabling or disabling logging, performing updates even if the read_only system variable is enabled, starting and stopping replication on slave servers, and allows you to connect (once) even if the connection limit controlled by the max_connections system variable is reached.

Conclusion:
If you have the PROCESS privilege, you can see all threads.
If you have the SUPER privilege, you can kill all threads and statements.
Otherwise, you can see and kill only your own threads and statements.
Reference: http://dev.mysql.com/doc/refman/4.1/en/kill.html

Impossible WHERE noticed after reading const tables

When I use explain it show me the below result

*************************** 1. row ***************************
id: 1
select_type: SIMPLE
table: NULL
type: NULL
possible_keys: NULL
key: NULL
key_len: NULL
ref: NULL
rows: NULL
Extra: Impossible WHERE noticed after reading const tables

mysql optimizer only work with data with match data.
else optimizer can't work

"Impossible WHERE noticed after reading const tables" mean mysql optimizer don't know estimated what index/ or it data should retrieve without data matching

MySQL Magazine - Issue 7

New magazine from the site

Issue 7

Performance Tuning Best Practices for MySQL

A video by Jay Pipes in one of Google’s Techtalk sessions recorded at 2006. A quit old talk but lot of useful information. Total lenght video around 45min. Take you time and go through on it

How to reset Password in mysql

Change you own password
login into mysql

at the "mysql>" prompt, type:
set password = password("yournewpassword");

Change other user password
SET PASSWORD FOR 'bob'@'%' = PASSWORD('yournewpassword')

Reference
12.4.1.6. SET PASSWORD Syntax

Addition information
Friend feedback and say he follow the instruction but change password fail! why ??
SET PASSWORD FOR 'user1'@'%localhost' = PASSWORD('yournewpassword')

We can check from here
login into mysql server
mysql> use mysql;
mysql> select user,host from user;

user | host |
+-------------+----------------------+
| root | mysqlserver
| user1 | localhost
| user2 | %

If we login and root and want change password for user1,
we should run this
SET PASSWORD FOR 'user1'@'localhost' = PASSWORD('yournewpassword')

if we want change password for user2,
we should run this
SET PASSWORD FOR 'user2'@'%' = PASSWORD('yournewpassword')

How to know which MYSQL Version I Using?

How to know which MYSQL Version I using

mysql -e status|grep 'Server version'
or
mysql -u root -p -e status|grep 'Server version'


Windows users:
mysql -e status

MySQL Magazine - Issue 6

New magazine from the site

Issue Six

SQL monitoring

We have MYSQL in production, and want have something like monitor or feedback on SQL status.

In MSSQL, we can do lot thing
Example : Monitor blocking, long query, job status

Google and find

1. mtop :
mytop is a console-based (non-gui) tool for monitoring the threads and overall performance of a MySQL 3.22.x, 3.23.x, and 4.x server.

more information

2. Find this script:


#!/bin/sh
# Variables
DBUSER=someone
DBPASS=something
SECONDS=15
# Main loop
while true
do
mysqladmin -u$DBUSER -p$DBPASS processlist |
egrep -vw 'Sleep|processlist|Binlog Dump' |
awk -F'|' '{print $6, $7, $8, $9}'
# First line of vmstat is historical, so take the second
vmstat 1 2 | tail -1
# Sleep for a while
sleep $SECONDS
done

3. MYSQLReport
mysqlreport makes a friendly report of important MySQL status values. mysqlreport transforms the values from SHOW STATUS into an easy-to-read report that provides an in-depth understanding of how well MySQL is running. mysqlreport is a better alternative (and practically the only alternative) to manually interpreting SHOW STATUS.

Anything else?