My Workday

JProfiler helps you find performance bottlenecks, pin down memory leaks and resolve threading issues in your Java application. JProfiler combines CPU, Memory and Thread profiling in one application and is developed by ej-technologies. The latest version at the time of this article is 6.0.

The new 5.5 is now available with “Semisynchronous Replication”. This comes as an addition to the built-in asynchronous replication. MySQL replication is asynchronous by default. Events written to the binary logs on the Master server being retrieved by the slave server(s). Unfortunately, the Master server has no knowledge of when the slave has retrieved or processed these events. As a result, when Master crashes, transactions committed on Master, might have not have been committed on the slave server(s). In other words, there is no guarantee that any event will ever reach any slave.

In case of “Semisynchronous Replication”, the Master server blockes the transaction commit until at least one of the slave servers acknowledges the it has received all the events for that transaction. Obviously, this is great for consistency, however it brings up questions about replication over the WWW which isn’t an uncommon practice. In case of hitting the timeout limit (in case of no response from any of the slave servers), the Master server reverts back to asynchronous replication.

From MySQL support:

To understand what the “semi” in “semisynchronous replication” means, compare it with asynchronous and fully synchronous replication:

* With asynchronous replication, the master writes events to its binary log and slaves request them when they are ready. There is no guarantee that any event will ever reach any slave.
* With fully synchronous replication, when a master commits a transaction, all slaves also will have committed the transaction before the master returns to the session that performed the transaction. The drawback of this is that there might be a lot of delay to complete a transaction.
* Semisynchronous replication falls between asynchronous and fully synchronous replication. The master waits after commit only until at least one slave has received and logged the events. It does not wait for all slaves to acknowledge receipt, and it requires only receipt, not that the events have been fully executed and committed on the slave side.

Software doesn’t just appear on the shelves by magic. That program shrink-wrapped inside the box along with the indecipherable manual and 12-paragraph disclaimer notice actually came to you by way of an elaborate path, through the most rigid quality control on the planet. Here, shared for the first time with the general public, are the inside details of the program development cycle.

1. Programmer produces code he believes is bug-free.
2. Product is tested. 20 bugs are found.
3. Programmer fixes 10 of the bugs and explains to the testing department that the other 10 aren’t really bugs.
4. Testing department finds that five of the fixes didn’t work and discovers 15 new bugs.
5. See 3.
6. See 4.
7. See 5.
8. See 6.
9. See 7.
10. See 8.
11. Due to marketing pressure and an extremely pre-mature product announcement based on overly-optimistic programming schedule, the product is released.
12. Users find 137 new bugs.
13. Original programmer, having cashed his royalty check, is nowhere to be found.
14. Newly-assembled programming team fixes almost all of the 137 bugs, but introduce 456 new ones.
15. Original programmer sends underpaid testing department a postcard from Fiji. Entire testing department quits.
16. Company is bought in a hostile takeover by competitor using profits from their latest release, which had 783 bugs.
17. New CEO is brought in by board of directors. He hires programmer to redo program from scratch.
18. Programmer produces code he believes is bug-free….

Verbose GC options

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Profiling Queries with SHOW STATUS
mysql> flush status;
mysql> select SQL_NO_CACHE count(*) from table;

- Check query plan now:

mysql> show status like 'Select%';

- Check engine operations:

mysql> show status like 'Handler%';

- Check if there was any ordering:

mysql> show status like 'Sort%';

- Check how many temporary tables have been created:

mysql> show status like 'Created%';


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Is a certain process running your CPU right into the ground? How do you find said process without picking your way through the ps aux results? With this command:

ps -e -o pcpu,cpu,nice,state,cputime,args --sort pcpu | sed '/^ 0.0 /d'

…at which point you can kill it with sudo kill -9.

The combination of FLUSH STATUS and SHOW SESSSION STATUS can be used to see what happens while MySQL executes a query. First, run FLUSH STATUS to reset session status variables to zero.

mysql> FLUSH STATUS;

mysql> SELECT COUNT(*) FROM TABLE;

Procedure to add a swap file

You need to use dd command to create swapfile. Next you need to use mkswap command to set up a Linux swap area on a device or in a file.

a) Login as the root user

b) Type following command to create 512MB swap file (1024 * 512MB = 524288 block size):

# dd if=/dev/zero of=/swapfile1 bs=1024 count=524288

c) Set up a Linux swap area:

# mkswap /swapfile1

d) Activate /swapfile1 swap space immediately:

# swapon /swapfile1

e) To activate /swapfile1 after Linux system reboot, add entry to /etc/fstab file. Open this file using text editor such as vi:

# vi /etc/fstab

Append following line:

/swapfile1 swap swap defaults 0 0

So next time Linux comes up after reboot, it enables the new swap file for you automatically.

g) How do I verify swap is activated or not?

Simply use free command:

$ free -m