Shantanu's Blog

In order to create hourly partitions, we need to use to_seconds function.
Here is a quick shell script to create the required hourly partitions for a given day.

#!/bin/sh
myval='2012-03-27'
mydate=${1:-$myval}
for ((a=0; a <= 24 ; a++))
do
parthour=`echo "$a hour" | sed 's/\ //'`
myhour=`mysql -Bse"select date_add('$mydate', interval $a hour)"`
echo "PARTITION $parthour VALUES less than (to_seconds('$myhour')),"
done

// create range daily partitions like this...
# sh create_partition.sh '2012-01-23' '2012-01-29'
PARTITION 20120123parti VALUES less than (to_seconds('2012-01-23 00:00:00')),
PARTITION 20120124parti VALUES less than (to_seconds('2012-01-24 00:00:00')),
PARTITION 20120125parti VALUES less than (to_seconds('2012-01-25 00:00:00')),
PARTITION 20120126parti VALUES less than (to_seconds('2012-01-26 00:00:00')),
PARTITION 20120127parti VALUES less than (to_seconds('2012-01-27 00:00:00')),
PARTITION 20120128parti VALUES less than (to_seconds('2012-01-28 00:00:00')),
PARTITION 20120129parti VALUES less than (to_seconds('2012-01-29 00:00:00')),

use following shell script

#!/bin/sh
mypart='parti'
start_date='2011-01-01'
myStartDate=${1:-$start_date}
end_date='2012-07-01'
myEndDate=${2:-$end_date}

start_seconds=`mysql -Bse"select to_seconds('$myStartDate')"`
end_seconds=`mysql -Bse"select to_seconds(date_add(('$myEndDate'), interval 1 day))"`
diff_seconds=$(($end_seconds-$start_seconds))

i="0"

while [ $i -lt $diff_seconds ]
do
myhour=`mysql -Bse"select date_add('$myStartDate', interval $i second)"`
partname=`mysql -Bse"select date_format(date_add('$myStartDate', interval $i second), '%Y%m%d')"`
echo "PARTITION $partname$mypart VALUES less than (to_seconds('$myhour')),"
i=$[$i+86400]
done

Labels: mysql, shell script

Inner join in redis

I've got a leader board set containing member ranks (roughly 2 million records) Each key has a corresponding hash set containing the member id, name,
gender and country. I'd like to be able to sort the leader board and also filter it by a field in the hash set (e.g.: *get scores for members where gender is male*).
What is the best approach to achieving this?

Ans:
sadd females laxmi kamal sonia
sadd male ram sham akbar

zadd scores 100 sonia
zadd scores 200 laxmi
zadd scores 300 kamal
zadd scores 100 ram
zadd scores 400 sham

zinterstore femscores 2 scores females
zrange femscores 0 50 withscores

Labels: redis

If you want to avoid 5 minute cron (*/5) you can set a per minute cron and check for 5 minute interval.
This will especially help when you already have per minute cron and want a command to run only after every 5 minutes.

cat todel.sh
#!/bin/sh
run_command='false'
myminute=`date '+%M'`
NUMBERS="5 10 15 20 25 30 35 40 45 50 55 00"
for number in `echo $NUMBERS`  
do
if [ $myminute -eq $number ];then
run_command='true'
break
else
run_command='false'
fi
done

if [[ $run_command == 'true' ]];then
echo "run command"
date

fi

Labels: shell script

Mysql can have daily partitions i.e. different partition for each day in a year. This shell script can help us to create the required code.

#!/bin/bash
# c is the numeric value of Jan 1, 2012
# a is the number of days in year

c=734502
for ((a=1; a <= 366 ; a++))
do
c=`expr $c + 1`
partition_name=`date '+%d%b%Y'  --date="2011-12-31 -$a day ago"`
echo "PARTITION $partition_name VALUES IN ($c),"
done

Labels: mysql, shell script

redis-py client objects and connection pools are designed to be threadsafe. And creating a client instance without explicitly specifying a connection pool creates one for you by default.

 
# redis_connections.py
cache = redis.StrictRedis(..., db=1)
testing = redis.StrictRedis(..., db=2)
...
# end redis_connections.py
 
 
# your application:
import redis_connections
redis_connections.cache.set('foo', 'bar')
...
redis_connection.testing.get('bing')

Labels: redis

// contents of showcode.php file

?php
$source = $file;
highlight_file( $source [ $return = false ] );

?>

It is possible that "return=false" may not work on older browsers and / or Linux OS. We can make any php file printable by passing the file name as variable in the URL. for e.g.

http://my_web_site.com/showcode.php?file=toprint.php

Labels: php tips, usability

Here are 2 very useful firefox extensions if you are using AWS account.

1) ElasticFox is a Mozilla Firefox extension for managing your Amazon EC2 account. Launch new instances, mount Elastic Block Storage volumes, map Elastic IP addresses, and more.

http://s3.amazonaws.com/ec2-downloads/elasticfox.xpi


2) s3fox allows you to manage S3 account just like any other FTP software.

https://addons.mozilla.org/en-US/firefox/addon/amazon-s3-organizers3fox/

Labels: aws

If you are having a project hosted on google code (and you should have one!) then the following steps will help you to upload a file to your downloads section.

1) Python script:
create the googlecode_upload.py on the server from where you want to upload a file.

wget http://support.googlecode.com/svn/trunk/scripts/googlecode_upload.py -o googlecode_upload_q7y2d4n8.py

2) credentials:
When you run the file, it will ask for your username that is usually the google username. But password is not the gmail password. You will see your password on the following page:

https://code.google.com/hosting/settings

Note your username and password.

3) Upload the file to your project:

# python google.py -s test -p mysqldump mysqldump.percona

summary (test), project name (mysqldump) and file name (mysqldump.percona) are required.

Labels: aws, usability

Here is the shell script that will generate 10 million lines of dummy records with a counter to keep all the records distinct. The data is delimited by ^
It should take less than 1 minute to generate the final tosend2.txt file.

# cat myredis.sh
#!/bin/bash
>tosend.txt
counter=0
while [ $counter -lt 200000 ]; do
echo "set 3969:$counter 14.140.90.242^^IN^mah^2012-02-29:12:17:17^^servFullEngine^^^UNTRUSTED/1.0:3agpp-agba^Generic^Mozilla:Midlet^$counter^^^^^^" >> tosend.txt
let counter=counter+1
done

for i in `seq 50`
do
sed 's/3969:/3969:'$i'0000/' tosend.txt >> tosend2.txt
done

# wc -l tosend2.txt
10000000 tosend2.txt

Labels: shell script

Labels: aws

Adjusting max connections:

As per my.cnf setting, the maximum permissible max connections are 1024 but we have used only 3 simultaneous connections so far. So there is no need of such a high value and it can be reduced to 900

[root@myserver]# mysqladmin variables | grep max_connections
| max_connections | 1024 |

[root@myserver]# mysqladmin extended-status | grep Max_used_connections
| Max_used_connections | 3 |

[root@myserver]# mysql -e"set global max_connections=600"

Now don't we have a risk of running out of available connections in the future?
Yes. we do. and we still need to keep the max connections as low as possible. why? read on.

table cache
In order to have better performance, we can set the table cache number very high. for e.g.

table_cache=1M

But it is wrong to set such a high value (one million !?), since mysql does not allow more than half a million size for this variable. Let mysql initially have the default limit of 64 that is sufficient for most usual operations. Increasing this limit will return "too many connections" error to the application that is going to be very costly. The high value of table cache conflicts with high value of max_connections and limit its usage. In other words trying to set table cache to 1 million will limit the max_connections to just around 200 or so because there is an upper limit of allowed open file descriptors set by OS.
This point will be clear if you see the following line in mysql error log ...

120201 19:40:24 [Warning] Changed limits: max_open_files: 1024 max_connections: 214 table_cache: 400

In the above case, Mysql has automatically adjusted the table_cache value from 1 million to 400. At the same time it has also brought down the max_connections value from 2000 to 214. This has been done because the max_open_files limit of 1024 is set by OS and mysql has no control over it. If we reduce the table_cache value to the default 64 then mysql will allow max_connections to be set higher than 214. Another option would be to increase the max_open_files variable using "ulimit" command from default 1024 to something like 4024. Since disabling "table_cache" option from my.cnf can easily resolve this issue, I do not recommend increasing file descriptors limit unless absolutely necessary.

In other words, disabling one million table_cache from my.cnf is the only easy option to avoid "max connections reached" error.

Default value of table cache is 64. If the number of file descriptors mysql needs to open is too high (in millions) only then we need to increase the table_cache variable.

[root@myserver]# mysqladmin variables | grep table_cache
| table_cache | 64 |

[root@myserver]# mysqladmin extended-status | grep Opened_tables
| Opened_tables | 1 million |

[root@myserver]# mysql -e"set global table_cache=512"

After restarting mysql service, always check the error log, there may be a useful warning!

Labels: mysql tips

If you are using MyISAM only database, key_buffer_size between 25% to 50% of total RAM is recommended. But it is also important to check if the allotted key buffer is really getting used.

my_key_blocks_unused=$((mysqladmin extended-status | grep Key_blocks_unused) | awk '{print $4}' )
my_key_cache_block_size=$((mysqladmin variables | grep key_cache_block_size) | awk '{print $4}' )
my_key_buffer_size=$((mysqladmin variables | grep key_buffer_size) | awk '{print $4}' )
echo "1 - (($my_key_blocks_unused * $my_key_cache_block_size) / $my_key_buffer_size)"

Once you execute the above commands at the command prompt, it will return something like this...

1 - ((38330 * 1024) / 67108864)

When this formula is evaluated (in excel or use calculator), it will return something like 0.4 and it means that half the key buffer is empty!

Here is how to increase key buffer from 64 MB to 8 GB:

# mysqladmin variables | grep key_buffer_size
| key_buffer_size | 67108864 |

# mysql -e"set global key_buffer_size = 67108864*128"

# mysqladmin variables | grep key_buffer_size
| key_buffer_size | 8589934592 |

_____

Tuning Primer shell script will do this calculation for you!

http://www.day32.com/MySQL/

Labels: mysql tips

Extra Packages for Enterprise Linux (EPEL) is a volunteer-based community effort from the Fedora project to create a repository of add-on packages for Red Hat Enterprise (RHEL) and its compatible spin-offs such as CentOS or Scientific Linux.
REMI is a repository created by Remi Collet. Here are the steps to install MySQL using Remi.

1.
rpm -Uvh http://dl.fedoraproject.org/pub/epel/5/x86_64/epel-release-5-4.noarch.rpm
rpm -Uvh http://rpms.famillecollet.com/enterprise/remi-release-5.rpm
yum --exclude=php\* --enablerepo=remi,remi-test install mysql mysql-server


2.
make following changes in my.cnf

#master-host=10.11.12.13
#master-user=repli
#master-password=secret
#master-connect-retry=60
#skip-locking
#skip-innodb

3. start mysql using following commands.
service mysqld start
if this fails to start mysql then use following commamd to start mysql

mysqld_safe --datadir=/mysql/data


make sure that you have all user grant information with you... so you can restore it after running mysql_install_db
mysql_install_db

#### /usr/share/mysql/english/errmsg.sys check for this file, if this file lines less then 14 lines the you have to copy this file from mysql-5.2 tar ###
#### use --exclude=php\* for excluding php package being update or downloaded

Labels: mysql

Labels: aws