Shantanu's Blog

Database Consultant

October 30, 2013

 

location of binary files


When you change the data directory do not forget to also change the data directory of binary logging as well as relay log position. If this is not changed, the binary or relay log may not be available when you mount / unmount the data directory.

datadir=/mnt/data/

log-bin=/mnt/bin/mysql/master
log-bin-index=appmaster

relay-log=/mnt/bin/relay/slave
relay-log-index=appslave

# you may need to create required directories
# mkdir -p /mnt/bin/relay/ /mnt/bin/mysql/

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October 29, 2013

 

killing and starting mysql service

Before you kill mysql process from command prompt it is very important to note the mysql parameters. Reading the following output carefully will save a lot of time later on.

root@ip-10-28:/usr# ps aux | grep mysql
root     15711  0.0  0.1   4400   752 pts/1    S    09:53   0:00 /bin/sh ./bin/mysqld_safe
root     16084  1.0 38.7 1584048 233956 pts/1  Sl   09:53   0:00 /usr/sbin/mysqld --basedir=/usr --datadir=/var/lib/mysql --plugin-dir=/usr/lib/mysql/plugin --user=root --pid-file=/var/run/mysqld/mysqld.pid --socket=/var/run/mysqld/mysqld.sock --port=3306

In order to start this mysql server again, I will need to change directory to the base directory /usr/ and from there start mysql using ./bin/mysqld_safe &

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October 25, 2013

 

TokuDB an engine of future


TokuDB is highly recommended for slaves in production environment. Here are 9 advantages of using TokuDB in production.

1) Data warehouse / big data solution:
TokuDB may take the same amount of time to complete the query if the data is small and fits in memory.
But with huge data, InnoDB is not able to perform while tokuDB gives you quick results.

2) Integrates with MySQL:
TOkuDB is an engine just like MyISAM and InnoDB. It is listed as default engine in the output of "show engines" command.

3) Highly compressed data:
TokuDB compresses data upto 15 to 20% compared to MyISAM or InnODB.

Tokudb disk consumption:
-rwxrwx--x 1 root root 222M Oct 25 19:27 _akola_ticket_main_41e0_1_18_B_0.tokudb
-rwxrwx--x 1 root root  68M Oct 25 19:27 _akola_ticket_key_tripindex_41e0_1_18_B_2.tokudb
-rwxrwx--x 1 root root  52M Oct 25 19:27 _akola_ticket_key_route_no_41e0_1_18_B_5.tokudb
-rwxrwx--x 1 root root  50M Oct 25 19:27 _akola_ticket_key_adjtripno_41e0_1_18_B_3.tokudb
-rwxrwx--x 1 root root  36M Oct 25 19:42 _akola_ticket_key_wbindex_41e0_1_18_B_1.tokudb
-rwxrwx--x 1 root root  34M Oct 25 19:27 _akola_ticket_key_NewIndex1_41e0_1_18_B_4.tokudb

MyISAM disk consumption for the same table:
-rw-rw---- 1 root root 1.5G Jul 10 00:36 ticket.MYD
-rw-rw---- 1 root root 335M Jul 10 00:40 ticket.MYI

4) Easily transfer data:
I can simply alter table to toku using alter table statement.

alter table tbl_name engine=TokuDB;

Or I can take the backup without specifing the engine. Since TokuDB is the default engine, it will be converted to tokudb while restoring data.

mysqldump db_name --routines --compatible=no_table_options > db_name_to_toku.sql

5) Crash Revoery:
TOkuDB has one of the excellent crash recovery feature just like InnoDB (that MyISAM is missing!)

6) Replication — Eliminate Slave Lag:
MySQL’s single threaded design often leads to slave lag. With TokuDB, slave lag is eliminated.
This insures replication can be used for read scaling, backups, and disaster recovery, without resorting to sharding, expensive hardware.

7) Hot Schema Changes in Seconds:
TokuDB introduced Hot Column Addition (HCAD). You can add or delete columns from an existing table with minimal downtime.

8) No need to configure parameters:
You may need to increase only open files limit if you get an error something like...
[ERROR] Error in accept: Too many open files
open-files-limit=40000

Other than this you do not need to configure anything! Now compare this with InnoDB.

By default, TokuDB uses about half the memory of the machine as buffer pool (or disk cache). That leaves the other half of memory for the OS to allocate.

9) InnoDB disk consumption:
InnoDB stores data in ibdata files and the disk consumption is not reduced even if you drop tables.
TokuDB tables works like MyISAM and frees the disk space immediately once you drop / truncate tables.

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October 24, 2013

 

Start and stop cluster using a script

Here is a python script that will start or stop the cluster as and when you wish from shell prompt.

Start the cluster based on the latest snapshot. It will not start a new cluster if there is one already running:
python redshift.py start

Delete the cluster after taking snapshot:
python redshift.py stop

The only requirement is that "boto" python module should be installed.
todo: There should be a clause to check if any process is using the cluster before deleting it. It is safe to delete a cluster if there is no process running.
_____

#!/usr/bin/python

import boto
conn = boto.connect_redshift(aws_access_key_id='ABC', aws_secret_access_key='XYZ+PQR')

import datetime
mymonth = datetime.datetime.now().strftime("%b").lower()
myday = datetime.datetime.now().strftime("%d")
myvar = mymonth+myday+'-vi-mar5-deliveryreport-new'

response = conn.describe_cluster_snapshots()
snapshots = response['DescribeClusterSnapshotsResponse']['DescribeClusterSnapshotsResult']['Snapshots']
snapshots.sort(key=lambda d: d['SnapshotCreateTime'])
mysnapidentifier = snapshots[-1]['SnapshotIdentifier']

mydict=conn.describe_clusters()

def start_cluster():
    try:
        myidentifier=mydict['DescribeClustersResponse']['DescribeClustersResult']['Clusters'][0]['ClusterIdentifier']
    except IndexError:
        conn.restore_from_cluster_snapshot('vi-mar5-deliveryreport-new', mysnapidentifier, availability_zone='us-east-1a')
        print "start a new cluster if no cluster is active"

def stop_cluster():
    try:   
        myidentifier=mydict['DescribeClustersResponse']['DescribeClustersResult']['Clusters'][0]['ClusterIdentifier']
        conn.delete_cluster(myidentifier, skip_final_cluster_snapshot=False, final_cluster_snapshot_identifier=myvar)
        print "stop cluster and take backup"
    except:
        print "No cluster is active right now"

import argparse

parser = argparse.ArgumentParser(description="Manage the cluster")
parser.add_argument("action", choices=["stop", "start"])

args = parser.parse_args()
print args
if args.action == "start":
    start_cluster()
if args.action == "stop":
    stop_cluster()

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