apache cassandra, part 3 – machinery, work with cassandra

April 12, 2023 www.ExigenServices.com

Apache Cassandra, part 3 – machinery, work with Cassandra

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V. Architecture (part 2)

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SEDA Architecture

SEDA – Staged event-driven architecture

1. Every unit of work is split into several stages that are executed in parallel threads.

2. Each stage consist of input and output event queue, event handler and stage controller.

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SEDA Architecture advantages

Well conditioned system load

Preventing resources from being overcommitted.

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SEDA in Cassandra - Usages

1. Read

2. Mutation

3. Gossip

4. Anti – Entropy

….

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SEDA in Cassandra - Design

Stage Manager presents Map between stage names and Java 5 thread pool executers.

Each controller with queue is presented by ThreadPoolExecuter that can be configured through JMX.

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VI. Working with Cassandra

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Installing and launching Cassandra

Download from http://cassandra.apache.org/download/

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Installing and launching Cassandra

Launching server: bin/cassandra.bat

– use “-f” key to run sever in foreground, so that all of the server logs will print to standard out

– is started with single node cluster called “Test Cluster” listening on port 9160

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Installing and launching Cassandra

Starting command-line client interface:bin/cassandra-cli.bat

– you see [username@keyspace] at the beginning of every line

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Creating a cluster

In configuration file cassandra.yaml specify:

seeds – the list of seeds for the cluster rpc_address and listen_address – network

addresses

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Creating a cluster

initial_token – defining the node’s token range auto_bootstrap – enables auto-migration of data

to the new node

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nodetool ring

Use nodetool for view configuration

~$ nodetool -h localhost -p 8080 ring

Address Status State Load Owns Range Ring

850705…

10.203.71.154 Up Normal 2.53 KB 50.00 0 |<--|

10.203.55.186 Up Normal 1.33 KB 50.00 850705… |-->|

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Connecting to server

Connect from command line:connect <HOSTNAME>/<PORT> [<USERNAME>

‘<PASSWORD>’];

Examples:connect localhost/9160;connect 127.0.0.1/9160 user ‘password’;

Connect when staring command line client:cassandra-cli –h,––host <HOSTNAME>

–p,––port <PORT>–k,––keyspace <KEYSPACE>–u,––username <USERNAME>–p,––password <PASSWORD>

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Describing environment

show cluster name;

show keyspaces;

show api version;

describe cluster;

describe keyspace [<KEYSPACE>];

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Create keyspace

create keyspace <KEYSPACE>; create keyspace <KEYSPACE> with

<ATTR1> = <VAL1> and<ATTR2> = <VAL2> ...;

Attributes:– placement_strategy– replication_factor– …

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Create keyspace

Example:create keyspace Keyspace1 with placement_strategy =

‘org.apache.cassandra.locator.RackUnawareStrategy’ and replication_factor = 4;

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Update keyspace

Update attributes of created keyspace:

update keyspace <KEYSPACE> with<ATTR1> = <VAL1> and <ATTR2> = <VAL2> ...;

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Switch to keyspace

use <KEYSPACE>; use <KEYSPACE> [<USERNAME> ‘<PASSWORD>’];

If you don’t specify username and password then credentials supplied to the ‘connect’ statement will be used

If the server doesn’t support authentication it will ignore credentials

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Switch to keyspace

Example:

use Keyspace1 user1 ‘qwerty123’;

When you use keyspace you’ll see [user1@Keyspace1] at the beginning of every line

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Create column family

create column family <COL_FAMILY>; create column family <COL_FAMILY> with

<ATTR1> = <VAL1> and<ATTR2> = <VAL1> ...;

Example:create column family Users with column_type = Super andcomparator = UTF8Type androws_cached = 1000;

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Update column family

When column family is created you can update its attributes:

update column family <COL_FAMILY> with<ATTR1> = <VAL1> and<ATTR2> = <VAL1> ...;

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Comparators and validators

Comparators – compare column names Validators – validate column values

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Comparators and validators

You can specify comparator for column family and all subcolumns in column family (one for all)

You can specify validators for each known column of column family

You can specify default validator for column family that will be used for columns for which validators aren’t specified

You can specify key validator which will validate row keys

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Attributes of column family

– column_type: can be Standard or Super(default - Standard)

– comparator: specifies how column names will be compared for sort order

– column_metadata: defines the validation and indexes for known columns

– default_validation_class: validator to use for values in columns which are not listed in the column_metadata. (default – BytesType)

– key_validation_class: validator for keys

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Column metadata

You can define validators for each known column in the family

create column family User withcolumn_metadata = [

{column_name: name, validation_class: UTF8Type},{column_name: age, validation_class:

IntegerType}, {column_name: birth, validation_class: UTF8Type}

];

Columns not listed in this section are validated with default_validation_class

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Secondary indexes

Allows queries by value

get users where name = ‘Some user';

Can be created in background

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Creating index

Define it in column metadata

For example in cassandra-cli:

create column family users with comparator=UTF8Type and column_metadata=[{

column_name: birth_date, validation_class: LongType, index_type: KEYS

}];

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Some restrictions

Cassandra use hash indexes instead of btree

indexes.

Thus, in where condition at least one indexed field

with operator “=“ must be present

So, you can’t use

get users where birth_date > 1970;

but can

get users where birth_date = 1990 and karma > 50;

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Index types

KEYS

BITMAP (will be supported in future releases)

Id GenderBitmaps

F M

1 Female 1 0

2 Male 0 1

3 Male 0 1

4 Unspecified 0 0

5 Female 1 0

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Writing data

To write data use set command:

set Customers[‘ivan’][‘name’] = ‘Ivan’;

set Customers[‘makar’][‘info’][‘age’] = 96;

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Reading data

To read data use get command:get Customers[‘ivan’][‘name’];

- this will display ‘Ivan’

get Customers[‘makar’];- this will display all columns for key ‘makar’

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Reading data

To list a range of rows use list command:list Customers;list Customers[a:];list Customers[a:c] limit 40;

- you can specify limit of rows that will be displayed (default - 100)

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Reading data

To get columns number use count command:count Customers[‘ivan’]

- this will display number of columns for key ‘ivan’

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Deleting data

To delete a row, a column or a subcolumn use del command:del Customers[‘ivan’];

- this will delete all columns for key ‘ivan’

del Customers[‘ivan’][‘name’];- this will delete column name for key ‘ivan’

del Customers[‘ivan’][‘accounts’][‘2312784829312343’];- this will delete a subcolumn with an account number from ‘accounts’ column for key ‘ivan’

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Deleting data

To delete all data in a column family use truncate command:

truncate Customers;

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Drop column family or keyspace

drop column family Customers;

drop keyspace Keyspace1;

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Q&A

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Resources

Home of Apache Cassandra Project http://cassandra.apache.org/

Apache Cassandra Wiki http://wiki.apache.org/cassandra/ Documentation provided by DataStax

http://www.datastax.com/docs/0.8/ Good explanation of creation secondary indexes

http://www.anuff.com/2010/07/secondary-indexes-in-cassandra.html

Eben Hewitt “Cassandra: The Definitive Guide”, O’REILLY, 2010, ISBN: 978-1-449-39041-9

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Authors

Lev Sivashov - lsivashov@gmail.com

Andrey Lomakin - lomakin.andrey@gmail.com, twitter: @Andrey_LomakinLinkedIn: http://www.linkedin.com/in/andreylomakin

Artem Orobets – enisher@gmail.comtwitter: @Dr_EniSh

Anton Veretennik - tennik@gmail.com