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Displaying posts with tag: mysql administration (reset)
VALIDATE PASSWORD PLUGIN with mysql_secure_installation in 5.7.7-rc

While testing installation steps with MySQL 5.7.7-rc, surely you will find much more improvements, changes, deprecated functionality and etc.

The interesting one is activating VALIDATE PASSWORD PLUGIN via mysql_secure_installation script. Which we use by mean “securing” MySQL installations.

I will write a separate topic about MySQL 5.7.7-rc installation steps from source, with related BUG reports.

So after first run:

[root@centos7_vm mysql]# bin/mysql_secure_installation --socket=/opt/mysql/datadir/mysqld-new.sock
Securing the MySQL server deployment.
Connecting to MySQL server using password in '/root/.mysql_secret'

If you notice, now script trying to connect to MySQL using a temporary password which is generated for root@localhost and logged into hidden .mysql_secret file.

VALIDATE PASSWORD PLUGIN can be used to test passwords
and improve security. It checks the strength of …
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Comprehensive guide to installing PXC on CentOS 7

Recently want to install Percona XtraDB Cluster + HAProxy + KeepAlived on CentOS 7, but could not find any all-in-one guide. So decided to write down all steps necessary for getting started and running HA solution using Open Source projects. Nowadays high availability is one of the main concerns faced by big and small companies.Minimum wasting of time (downtime per year), sustainably working of infrastructure and etc. is the main mission for all companies that they are trying to achieve.There are different approaches to this mission. One of them as large companies did, to buy expensive software and support from vendors. But small companies could not go through these steps. The true power of Open Source comes up at these moments.You can build your own High Availability solution using free but yet powerful Open Source projects. In this article we will show you how to achieve Database Clustering and Load Balancing. We will use:

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MySQL Optimizer Tracer usage case with count(*)

What is Optimizer Trace? After reading topic about Optimizer Tracer by [Morgan Tocker][1] decided to test it. From [Optimizer Trace and EXPLAIN FORMAT=JSON in 5.7][2]: Optimizer trace is a new diagnostic tool introduced in MySQL 5.6 to show how the optimizer is working internally. It is similar to EXPLAIN, with a few notable differences: It doesn’t just show the intended execution plan, it shows the alternative choices. You enable the optimizer trace, then you run the actual query. It is far more verbose in its output. For understanding goal of article please read previous one about related verified optimizer BUG: [Playing with count() optimizer work][3] ** We have 2 queries: **select count() from sales; select count(*) from sales where sales_id > 0; Firstly let’s get explain plan for query with JSON format and as regular:

       -- JSON 
          mysql> explain format=json select …
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MySQL LogRotate script

Did you ever try to use log rotate facility in Linux with MySQL? There is no need to script one for this purpose, it is already installed. From MySQL spec file, it looks for logrotate.d folder:

    # Ensure that needed directories exists 
    install -d $RBR%{_sysconfdir}/{logrotate.d,init.d}

As well as there is dedicated script for installing logrotate script. The script path is: /mysql-5.6.24/support-files/ Again from spec file:

    # Install logrotate and autostart 
    install -m 644 $MBD/release/support-files/mysql-log-rotate $RBR%{\_sysconfdir}/logrotate.d/mysql

After installing there will be mysql script in /etc/logrottate.d/.

   # The log file name and location can be set in
   # /etc/my.cnf by setting the "log-error" option
   # in either [mysqld] or [mysqld_safe] section as
   # follows: …
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Partial table recovery from physical backup

In previous topic, we have covered “Transportable Tablespace” concept by copying and importing table’s tablespace to remote server. See -> Copying Tablespaces to Remote Server

The idea is copying tablespace file to remote server, in remote server you must create identical database names and table names manually, then you should discard new table’s tablespace file and import new copied one.

To achieve this you must have running MySQL version >= 5.6, innodb_file_per_table=1 and you must know “CREATE statement” of table.

Let’s to change our test condition. Assume that, you have MySQL server and you have taken physical backup of your server (you can use Percona XtraBackup, …

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lower_case_table_names option to lose databases and tables

To lose your data or make it unavailable there is an excellent option in MySQL, rather than drop or delete Option name is lower_case_table_names. Default value of this setting is 0:

       mysql> select @@lower_case_table_names; 
       | @@lower_case_table_names | 
       | 0 | 
       1 row in set (0.00 sec) 

Due to documentation value=0: Table and database names are stored on disk using the lettercase specified in the CREATE TABLE or CREATE DATABASE statement. Name comparisons are case sensitive. You should not set this variable to 0 if you are running MySQL on a system that has case-insensitive file names (such as Windows or OS X). If you force this variable to 0 with –lower-case-table-names=0 on a case-insensitive file system and access MyISAM tablenames using different …

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Error reading GTIDs from binary log: -1

Wonder how MySQL Slave server will act, when disk full condition occurs? Before in our articles we use only single MySQL server. Now think about replication topology, where slave server has problem with full partition. Firstly we will enable Binary Log/GTID on Slave side and will ensure that the changes also applied to binary log on Slave side:

      server_id = 2 
      log_bin = /opt/mysql/datadir/mysql-bin 
      log_bin_index = /opt/mysql/datadir/mysql-bin 
      expire_logs_days = 14 
      sync_binlog = 1 
      binlog_format = row 
      relay_log = /opt/mysql/datadir/mysql-relay-bin 
      log_slave_updates = 1 
      read_only = 1 
      gtid-mode = on 
      enforce-gtid-consistency = true 
      master-info-repository = TABLE 
      relay-log-info-repository = TABLE 
      slave-parallel-workers = 15 
      binlog-checksum = CRC32 
      master-verify-checksum = 1 
      slave-sql-verify-checksum = 1 …
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Testing MySQL with “read-only” filesystem

From previous articles about “disk full” conditions, you have some taste of testing MySQL with such approach:

1. Testing Disk Full Conditions

2. Using GDB, investigating segmentation fault in MySQL

But there is still untouched topic, about read-only mounted file system and how MySQL will act in such condition. In real life, i have encountered such situation that something happened with Linux server and file system suddenly goes to read-only mode.

Buffer I/O error on device sdb1, logical block 1769961 lost page write due to I/O error on sdb1 sd 0:0:1:0: timing out command, waited 360s sd 0:0:1:0: Unhandled error code sd 0:0:1:0: SCSI error: return code = 0x06000008 Result: hostbyte=DID_OK …
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Using GDB, investigating segmentation fault in MySQL

In previous article, we have covered some errors and issues with using MySQL in “disk full” environment. Where there was no space left on device.(See here: Testing Disk Full Conditions)

Today’s scenario is -> Starting MySQL with GTID/binary log enabled, in 0 space left Linux(CentOS 6.5) environment.

If you hit a bug or problem, general rule for helping community to fix it is to provide as much information as possible. Especially useful is to give gdb output from coredump. To get coredump you can read this wonderful article Hunting-The-Core

Now let’s explore our situation. Because our segfault is detected while starting MySQL, it is not possible to attach PID to GDB and also using strace. Our my.cnf file:

log_bin = …
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Testing “disk full” conditions in MySQL

How MySQL will act if there is no space left on hard disk?
To answer this question, let’s test it:

Our first test is with MySQL 5.6.24-debug with disabled binary log:
Trying to import huge dump, after while it says table is full:

Query OK, 12725 rows affected (2.46 sec)
Records: 12725  Duplicates: 0  Warnings: 0

Query OK, 12724 rows affected (2.40 sec)
Records: 12724  Duplicates: 0  Warnings: 0

Query OK, 12726 rows affected (2.53 sec)
Records: 12726  Duplicates: 0  Warnings: 0

ERROR 1114 (HY000): The table 'sales' is full
ERROR 1114 (HY000): The table 'sales' is full
ERROR 1114 (HY000): The table 'sales' is full

In error log you will see something like:

[root@localhost mysql]# tail -f /opt/mysql/datadir/error.err
Version: '5.6.24-debug'  socket: '/opt/mysql/datadir/mysqld-new.sock'  port: 3307  Shahriyar Rzayev's MySQL
2015-04-24 03:56:09 7fabeffff700 InnoDB: Error: Write to file ./sales2/sales.ibd failed at …
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