Shantanu's Blog

Corporate Consultant

September 27, 2013

 

Optimum size of varchars

Here is an excellent explanation about why the varchars should not be more than their optimum size.

MySQL materializes query results to a temporary table, using the MEMORY engine if it can, then converting to MyISAM if it gets too big. The MEMORY engine doesn't support variable length rows, so VARCHARs are converted to CHARs. The field `d` only contains one character in each row, but is defined as a VARCHAR(20000) - which means the temporary table will grow very large. Even when converted to MyISAM, it retains that fixed width format, so the temp table is huge.

Source: http://thenoyes.com/littlenoise/?p=167

Another reason is that the limit of 750 characters on creating indexes may come into the picture. Loosely declared columns can not be indexed properly and composite indexes are almost impossible.

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September 26, 2013

 

Using boto to manage EC2 instances

Amazon Web Services GUI console is really user-friendly. But how about creating / stopping an instance using just 2 or 3 commands? You need python's boto module installed.
 1) Choose any one of the following images:
Red Hat Enterprise Linux 6.4 - ami-a25415cb / ubuntu ami-599c1730 / tokuDB ami-eba0f882 / infinidb ami-25065e4c

2) Choose any one of the following instance type:
General Purpose: t1.micro (0.02), m1.small (2GB - $0.06), m1.medium (4GB - $0.12), m1.large (8GB - $0.24), m1.xlarge (15GB - $0.48), m3.xlarge (15 GB - $0.50), m3.2xlarge (30GB - $1.0)
memory optimizied:  m2.xlarge (16 GB - 0.41) , m2.2xlarge (34 GB - 0.82), m2.4xlarge ( 68GB - 1.64)
storage optimized : hi1.4xlarge (60GB - 3.1), hs1.8xlarge (117GB - 4.6)
Computer optimized:  c1.medium (2GB - 0.145), c1.xlarge (8 GB - 0.58)

import boto.ec2
conn = boto.ec2.connect_to_region("us-east-1", aws_access_key_id='ABC', aws_secret_access_key='ABC+XYZ')
conn.run_instances('ami-a25415cb', placement='us-east-1a', key_name='nov15a',instance_type='m1.xlarge',security_groups=['NuoD-1-0-1-AutogenByAWSMP-'])
<< Reservation:r-50b4f837


// you can also use redhat centos 64 bit version
// AMI: RHEL-6.4_GA-x86_64-10-Hourly2 (ami-a25415cb)


>>> reservations = conn.get_all_instances()
>>> reservations
[Reservation:r-cded15ae, Reservation:r-50b4f837]

>>> instances = reservations[1].instances
>>> instances
[Instance:i-ce07b5b5]

conn.get_all_instances(filters={'reservation-id': 'r-50b4f837'})[0].instances[0]
Instance:i-ce07b5b5


# finding public dns from instance id      
reservations = conn.get_all_instances(instance_ids=['i-ce07b5b5'])
     
#pull out our single instance      
instance = reservations[0].instances[0]
     
#Now we've got the full instance and we can get parameters from here
print(instance.public_dns_name)
<<< ec2-54-226-72-238.compute-1.amazonaws.com


// or get the public dns using
conn.get_all_instances(filters={'reservation-id': 'r-50b4f837'})[0].instances[0].public_dns_name


>>> inst = instances[0]
>>> inst.instance_type
u'm1.xlarge'

// ## start, stop or terminate instance

conn.stop_instances(instance_ids=['i-ce07b5b5'])

conn.start_instances(instance_ids=['i-ce07b5b5'])

conn.terminate_instances(instance_ids=['i-ce07b5b5'])


// attach a given volume from the same zone to the instance
conn.attach_volume ('vol-4a825709', 'i-c77aa3bf', '/dev/sdx')

Upload / download / delete file

import boto
from boto.s3.connection import OrdinaryCallingFormat
c = boto.connect_s3('ABC','PQR+XYZ',calling_format=OrdinaryCallingFormat())
mybucket = c.get_bucket('Vignesh_import')

from boto.s3.key import Key
k = Key(mybucket)
k.key = 'boto.zip'
k.set_contents_from_filename('develop.zip')

for b in mybucket:
    if b.name == 'boto.zip':
         b.get_contents_to_filename('boto.zip')

mybucket.delete_key('boto.zip')

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