MySQL 5.7 for production

With the time MySQL as database getting better in terms of High performance , scalability and security.
MySQL 5.7 new features : http://dev.mysql.com/doc/refman/5.7/en/mysql-nutshell.html

As a MySQL user my favorites are from above list:

  •  New options for replication :
    Changing replication filters online including and excluding table/db and enabling GTID transaction online.
  •  InnoDB related changes:
    Online buffer pool resize and many defaults are changed to more secure and optimized values.
  • Security features :
    Improved User authentication like default users, SSL and data encryption with key capabilities in order to secure overall database.
  • Monitoring and analysis statistics :
    Improved performance schema for live transactions analysis which we can not mostly find out with SHOW PROCESSLIST command or Be Using INFORMATION_SCHEMA database tables.
  • All in this very important is “Setting configuration variables dynamically while a server is running.This change will save many downtimes or mysqld service restarts.
  • Optimizer:
    New optimizer changes will be the one doing magic inside for Query performance.

Something New :

  • Multi-source replication
  • Innodb tablespace encryption using key
  • MySQL x-protocol and Document store using JSON datatype capabilities.
  • Optimized and secure defaults settings for initial MySQL database setup.

I believe these are the most imported MySQL database areas used by MySQL user in the production environment.

How many of you using mysql-5.7 in production or planning for implementation in future? Please share your experience with it.

Mysql table locking

Locking is important in many scenarios to prevent other sessions from modifying tables during periods when a session requires exclusive access to them. for example altering table definition online or any kind of table definition changes.locking Mysql provides an option to lock table/s with different types of locks, depends on need.

syntax for lock table:

LOCK TABLES
    tbl_name [[AS] alias] lock_type
    [, tbl_name [[AS] alias] lock_type] ...

lock_type:
    READ [LOCAL]
  | [LOW_PRIORITY] WRITE

UNLOCK TABLES

Following are the examples for READ and WRITE LOCK:

READ LOCK:

session1> create table t1( c1 int);
Query OK, 0 rows affected (0.06 sec)

session1> insert into test.t1 values(1001);
Query OK, 1 row affected (0.01 sec)

session1> lock table t1 READ;
Query OK, 0 rows affected (0.00 sec)

session1> select count(*) from t1;
+----------+
| count(*) |
+----------+
| 1 |
+----------+
1 row in set (0.00 sec)
session1> insert into t1 values(1002);
ERROR 1099 (HY000): Table 't1' was locked with a READ lock and can't be updated

Session1 acquired READ lock on table t1 explicitly. After applying READ lock on table users can read the table but not write it.

session2> lock table t1 READ;
Query OK, 0 rows affected (0.00 sec)

session2> insert into t1 values(1002);
ERROR 1099 (HY000): Table 't1' was locked with a READ lock and can't be updated

session3> select * from t1;
+------+
| c1 |
+------+
| 1001 |
+------+
1 row in set (0.00 sec)

Multiple sessions can acquire a READ lock on the table at the same time and other sessions can read the table without explicitly acquiring a READ lock.

currently, READ lock s acquired by session1 and session2, both locks need to be unlocked in order to perform a write operation on lock table.

session1> UNLOCK TABLES;
session1> insert into t1 values(1005);

INSERT operation executed from session1  will go in waiting state, since READ lock acquired on table t1 by session2 and not  released yet.

You can see this using:

session3> show processlist;
+----+------+-----------+------+---------+------+---------------------------------+----------------------------------+
| Id | User | Host | db | Command | Time | State | Info |
+----+------+-----------+------+---------+------+---------------------------------+----------------------------------+
| 2 | session1 | localhost | test | Query | 89 | Waiting for table metadata lock | insert into test.t1 values(1005) |
| 3 | session3 | localhost | test | Query | 0 | starting | show processlist |
| 4 | session2 | localhost | test | Sleep | 77 | | NULL |
+----+------+-----------+------+---------+------+---------------------------------+----------------------------------+
3 rows in set (0.00 sec)

After releasing READ lock by session2 insert operation will execute on t1 table.

session2> UNLOCK TABLES;
session1>  select * from t1;
+------+
| c1 |
+------+
| 1001 |
| 1005 |
+------+
2 rows in set (0.00 sec)

NOTE: FLUSH TABLES Different form UNLOCK TABLES:

FLUSH TABLE:  Closes all open tables, forces all tables in use to be closed, and flushes the query cache. FLUSH TABLES also removes all query results from the query cache, like the RESET QUERY CACHE statement. FLUSH TABLE will not work when table acquires READ LOCK.

UNLOCK TABLES: UNLOCK TABLES explicitly releases any table locks held by the current session. LOCK TABLES implicitly releases any table locks held by the current session before acquiring new locks.

********************************************************************************************************************************************

WRITE LOCK:

-The session that holds the lock can read and write the table.

session1> lock table t1 write;
Query OK, 0 rows affected (0.00 sec)

session1> insert into test.t1 values(1006);
Query OK, 1 row affected (0.01 sec)

session1> select count(*) from t1;
+------+
| c1 |
+------+
| 1001 |
| 1005 |
| 1006 |
+------+
3 rows in set (0.00 sec)

-Only the session that holds the lock can access the table. No other session can access it until the lock is released.

session2> select count(*) from t1;
and 
session3> insert into test.t1 values(1002);

session1> show processlist;
+----+------+-----------+------+---------+------+---------------------------------+----------------------------------+
| Id | User | Host | db | Command | Time | State | Info |
+----+------+-----------+------+---------+------+---------------------------------+----------------------------------+
| 2 | session1 | localhost | test | Query | 0 | starting | show processlist |
| 3 | session2 | localhost | test | Query | 127 | Waiting for table metadata lock | select count(*) from t1 |
| 4 | session3 | localhost | test | Query | 116 | Waiting for table metadata lock | insert into test.t1 values(1002) |
+----+------+-----------+------+---------+------+---------------------------------+----------------------------------+
3 rows in set (0.00 sec)

Look into performance_schema.metadata_locks table for more status information on table locks. (Thanks for the hint daniel )

– Enable Locking related instruments (if it’s not enabled) :

UPDATE performance_schema.setup_instruments SET ENABLED=’YES’, TIMED=’YES’ WHERE NAME=’wait/lock/metadata/sql/mdl’;

SELECT * FROM performance_schema.metadata_locks WHERE OBJECT_SCHEMA=’test’ AND OBJECT_NAME LIKE ‘t_’;

-Lock requests for the table by other sessions block while the WRITE lock is held.

All set  :) ……

[ERROR] COLLATION ‘utf8_general_ci’ is not valid for CHARACTER SET ‘latin1’

Recently came across the problem where mysql server stop running and refusing to start with an error

The server quit without updating PID file (/var/run/mysqld/mysqld.pid)

Checked Mysql error log and found that an invalid usage of charset with collation causing problem.

error log:
141017 12:20:41 mysqld_safe Starting mysqld daemon with databases from /usr/local/mysql/data
while 15088 [ERROR] COLLATION 'utf8_general_ci' is not valid for CHARACTER SET 'latin1'
15088 [ERROR] Aborting

In this case mysqld trying to start  with  character-set-server = latin1 and collation-server = utf8_general_ci, which is not valid.
The following is the right charset value for COLLATION ‘utf8_general_ci’

node1 [localhost] {msandbox} ((none)) > SHOW COLLATION LIKE ‘utf8_general_ci’;

+—————–+———+—-+———+———-+———+

| Collation       | Charset | Id | Default | Compiled | Sortlen |

+—————–+———+—-+———+———-+———+

| utf8_general_ci | utf8    | 33 | Yes     | Yes      |       1 |

+—————–+———+—-+———+———-+———+

Solution:

Add following options in my.cnf

character-set-server = utf8
collation-server = utf8_general_ci
character-set-client-handshake = false

And start  mysql server.It will start without any error.

ALL SET.

linux swap and mysql memory

After mysql installation, To make mysql server production ready we have to tune default mysql variables considering the hardware, production load, performance, durability etc.

But What about the optimizing  Linux OS settings  with mysql ?

mysql-linux1

Here it is, i encountered  an issue once when i was checking TOP output for mysqld process and found that the mysqld  memory continuously increasing. Also there was one more thing  that it was using swap memory even if there was enough RAM memory available. we have monitored for a week and this was causing an issue like slow query processing, performance and slowness on DB server.

To solve this problem we have to set correct swappiness

  •       To check vm.swappiness

                    cat /proc/sys/vm/swappiness    (Default value : 60 (Range 0 to 100))

  •    To set a new non-persistent value :

                     sysctl -w vm.swappiness=0

  •    To set a new persistent value :

                     add vm.swappiness=0 in the /etc/sysctl.conf file

All Set !!

About SWAP space:

The swappiness parameter controls the tendency of the kernel to move processes out of physical memory and onto the swap disk. Because disks are much slower than RAM, this can lead to slower response times for system and applications if processes are too aggressively moved out of memory.

  1. swappiness can have a value of between 0 and 100
  2. swappiness=0 tells the kernel to avoid swapping processes out of physical memory for as long as possible
  3. swappiness=100 tells the kernel to aggressively swap processes out of physical memory and move them to swap cache

Following are basic instructions for checking swappiness, emptying your swap and changing the swappiness to 0:

To check memory usage status :

          free

To check the swappiness value:

         cat /proc/sys/vm/swappiness

To turn swapoff :
This will empty your swap and transfer all the swap back into memory. First make sure you have enough memory available by viewing the resources tab of gnome-system-monitor, your free memory should be greater than your used swap. This process may take a while, use gnome-system-monitor to monitor and verify the progress.

sudo swapoff -a

To set the new value to 0:

echo 0 | sudo tee /proc/sys/vm/swappiness

To turn swap back on:

sudo swapon -a

mysql geographical replication lag

Recently while working on geographical master slave replication we encountered an issue, where in peak hours replication slave lagging.

when we checked SHOW SLAVE STATUS value of Seconds_Behind_Master was jumping from 0 to a random high value, and then back to 0.

We also found this in the processlist of Master,

1366318 rpluser [IP Address]:15120  NULL  Binlog  Dump   9033    Writing to net  NULL

The status “Writing to net” means that MASTER is sending (or trying to send) data to SLAVE.

In a healthy replication, the status would be “Has sent all binlog to slave; waiting for binlog to be updated“.

It usually happens when MASTER-SLAVE geographically distributed in different data-center,network , and slow network.

Here limited network bandwidth was causing a problem , and we needed a solution to compress the transmission between the master and slave databases. MySQL provides a variable, which is dynamic and is set on the slave: slave_compressed_protocol=1

If this option is set to 1, use compression for the slave/master protocol if both the slave and the master support it. The default is 0 (no compression).

changes on slave:

show global variables like 'slave_compressed_protocol';   //default OFF

stop slave;

set global slave_compressed_protocol=1;

start slave;

show global variables like 'slave_compressed_protocol';     // ON

Also,  check PROCESSLIST on master and replication user status,

ALL SET!!

FreeRadius 3.0.x Installation and configuration with Mysql

This document describes how to setup a FreeRADIUS server. A MySQL server is used as backend and for the user accounting.

RADIUS is an industry-standard protocol for providing authentication, authorization, and accounting services.

  • Authentication is the process of verifying a user’s identity and associating additional information (attributes) to the user’s login session.
  • Authorization is the process of determining whether the user is allowed on the network and controlling network access values based on a defined security policy.
  • Accounting is the process of generating log files that record session statistics used for billing, system diagnosis, and usage planning.

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