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Displaying posts with tag: myisam (reset)
How lsof Utility May Help MySQL DBAs

While working in Support, I noticed that probably at least once a week I have to use or mention lsof utility in some context. This week, for example, we had a customer trying to find out if his mysqld process running is linked with tcmalloc library. He started it different ways, using LD_PRELOAD directly and --malloc-lib option of mysqld_safe script etc, but wanted to verify that his attempts really worked as expected. My immediate comment in the internal chat was: "Just let them run lsof -p `pidof mysqld` | grep mall and check!" My MariaDB 10.2 instance uses jemalloc and this can be checked exactly the same way:
openxs@ao756:~/dbs/maria10.2$ ps aux | grep mysqld...
openxs    4619  0.0  0.0   4452   804 pts/2    S    …

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MySQL, Percona Server for MySQL and MariaDB Default Configuration Differences

In this blog post, I’ll discuss some of the MySQL and MariaDB default configuration differences, focusing on MySQL 5.7 and MariaDB 10.2. Percona Server for MySQL uses the same defaults as MySQL, so I will not list them separately.

MariaDB Server is a general purpose open source database, created by the founders of MySQL. MariaDB Server (referred to as MariaDB for brevity) has similar roots as Percona Server for MySQL, but is quickly diverging from MySQL compatibility and growing on its own. MariaDB has become the default installation for several operating systems (such as Red Hat Enterprise Linux/CentOS/Fedora). Changes in the default variables can make a large difference in the out-of-box …

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Why we still need MyISAM (for read-only tables)

TL;DR: we still need MyISAM and myisampack because it uses less space on disk (half of compressed InnoDB) !

In the previous post, I shared my experience with InnoDB table compression on a read-only dataset.  In it, I claimed, without giving much detail, that using MyISAM and myisampack would result is a more compact storage on disk.  In this post, I will share more details about this claim.

An Adventure in InnoDB Table Compression (for read-only tables)

In my last post about big MySQL deployments, I am quickly mentioning that InnoDB compression is allowing dividing disk usage by about 4.3 on a 200+ TiB dataset.  In this post, I will give more information about this specific use case of InnoDB table compression and I will share some statistics and learnings on this system and subject.  Note that I am not covering InnoDB page compression which is

How far can you go with MySQL or MariaDB ?

MySQL theoretical limits are known and they can be found in the manual, they include:

MyISAM permits data and index files to grow up to 256 TiB by default, but this limit can be changed up to the maximum permissible size of 65,536 TiB (256^7 − 1 bytes). The maximum tablespace size depends on the InnoDB page size: 64 TiB for 16 KiB pages.(The maximum tablespace size is also the maximum size for a

Why Thread May Hang in "Waiting for table level lock" State - Part I

Last time I had to use gdb to check what's going on in MySQL server and found something useful with it to share in the blog post it was April 2017, and I miss this kind of experience already. So, today I decided to try it again in a hope to get some insights in cases when other tools may not apply or may not be as helpful as one could expect. Here is the long enough story, based on recent customer issue I worked on this week.
* * * Had you seen anything like this output of SHOW PROCESSLIST statement:

Id User Host db Command Time State 
Info Progress
...
28 someuser01 xx.xx.xx.xx:39644 somedb001 Sleep 247
NULL 0.000
29 someuser01 xx.xx.xx.yy:44100 somedb001 Query 276
Waiting for table level lock DELETE FROM t1 WHERE (some_id = 'NNNNN') AND ...
0.000 …
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Fun with Bugs #47 - On Some Bugs Found Using oprofile

Users had to identify the reasons for MySQL performance problems somehow well before famous Performance Schema appeared in MySQL 5.5.3, and even before Domas invented his Poor Man's Profiler. Poor users had to use some OS-level tools, and among these tools the most important one was, probably, oprofile.

oprofile is a system-wide statistical profiling tool for Linux available since 2001 and 2.4.x kernels. It was applied to MySQL for many …

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MySQL 8.0: The end of MyISAM

This blog discusses the gradual end of MyISAM in MySQL.

The story that started 20 years ago is coming to its end. I’m talking about the old MyISAM storage engine that was the only storage provided by MySQL in 1995, and was available in MySQL for 20+ years. Actually, part of my job as a MySQL consultant for 10+ years was to discover MyISAM tables and advise customers how to convert those to InnoDB.

(Check your MySQL installation, you may still have MyISAM tables).

MySQL 5.7 still used MyISAM storage for the system tables in the MySQL schema.

In MySQL 8.0 (DMR version as of writing), the MyISAM storage engine is still available. But in a very limited scope:

  • After …
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Q: Does MySQL support ACID? A: Yes

I was recently asked this question by an experienced academic at the NY Oracle Users Group event I presented at.

Does MySQL support ACID? (ACID is a set of properties essential for a relational database to perform transactions, i.e. a discrete unit of work.)

Yes, MySQL fully supports ACID, that is Atomicity, Consistency, Isolation and Duration. (*)

This is contrary to the first Google response found searching this question which for reference states “The standard table handler for MySQL is not ACID compliant because it doesn’t support consistency, isolation, or durability”.

The question is however not a simple Yes/No because it depends on timing …

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corrupted / crashed MyISAM + mysql_repair_threads = stuck “Repair with N threads”

This post explains on the usage of mysql_repair_threads for repairing myisam table & the processlist status Repair with N threads

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