I'm starting to learn cassandra. So far I have created a keyspace. Next, I simply want to create a column family. Reading docs, this should simply be:
create column family DATASTORE;
I keep getting the error:
Bad Request: line 1:7 no viable alternative at input 'column'
Installed Cassandra on windows.
I'm using Cassandra CQL.
Thanks.
I suggest reading the "Creating a table with CQL" section of the docs.
This command is only appropriate for the CLI Utility application - and is not valid CQL. This video provides a good overview: https://www.youtube.com/watch?v=WSCrwBueoPI&list=PL3E5AC388940EEC0A
You need to supply more parameters to dictate what the table (also known as a column family) will store.
First create a keyspace (the below is in cql)
CREATE KEYSPACE firstkeyspace
WITH REPLICATION =
{
'class': 'SimpleStrategy',
'replication_factor': '2'
}
Then here is what you want. This will create a table named userz in the firstkeyspace keyspace. The below table will store two columns (columns as in columns of a table).
CREATE TABLE firstkeyspace.userz (
user text,
password text,
PRIMARY KEY (user)
);
Related
In several places it's advised to design our Cassandra tables according to the queries we are going to perform on them. In this article by DataScale they state this:
The truth is that having many similar tables with similar data is a good thing in Cassandra. Limit the primary key to exactly what you’ll be searching with. If you plan on searching the data with a similar, but different criteria, then make it a separate table. There is no drawback for having the same data stored differently. Duplication of data is your friend in Cassandra.
[...]
If you need to store the same piece of data in 14 different tables, then write it out 14 times. There isn’t a handicap against multiple writes.
I have understood this, and now my question is: provided that I have an existing table, say
CREATE TABLE invoices (
id_invoice int PRIMARY KEY,
year int,
id_client int,
type_invoice text
)
But I want to query by year and type instead, so I'd like to have something like
CREATE TABLE invoices_yr (
id_invoice int,
year int,
id_client int,
type_invoice text,
PRIMARY KEY (type_invoice, year)
)
With id_invoice as the partition key and year as the clustering key, what's the preferred way to copy the data from one table to another to perform optimized queries later on?
My Cassandra version:
user#cqlsh> show version;
[cqlsh 5.0.1 | Cassandra 3.5.0 | CQL spec 3.4.0 | Native protocol v4]
You can use cqlsh COPY command :
To copy your invoices data into csv file use :
COPY invoices(id_invoice, year, id_client, type_invoice) TO 'invoices.csv';
And Copy back from csv file to table in your case invoices_yr use :
COPY invoices_yr(id_invoice, year, id_client, type_invoice) FROM 'invoices.csv';
If you have huge data you can use sstable writer to write and sstableloader to load data faster.
http://www.datastax.com/dev/blog/using-the-cassandra-bulk-loader-updated
To echo what was said about the COPY command, it is a great solution for something like this.
However, I will disagree with what was said about the Bulk Loader, as it is infinitely harder to use. Specifically, because you need to run it on every node (whereas COPY needs to only be run on a single node).
To help COPY scale for larger data sets, you can use the PAGETIMEOUT and PAGESIZE parameters.
COPY invoices(id_invoice, year, id_client, type_invoice)
TO 'invoices.csv' WITH PAGETIMEOUT=40 AND PAGESIZE=20;
Using these parameters appropriately, I have used COPY to successfully export/import 370 million rows before.
For more info, check out this article titled: New options and better performance in cqlsh copy.
An alternative to using COPY command (see other answers for examples) or Spark to migrate data is to create a materialized view to do the denormalization for you.
CREATE MATERIALIZED VIEW invoices_yr AS
SELECT * FROM invoices
WHERE id_client IS NOT NULL AND type_invoice IS NOT NULL AND id_client IS NOT NULL
PRIMARY KEY ((type_invoice), year, id_client)
WITH CLUSTERING ORDER BY (year DESC)
Cassandra will fill the table for you then so you wont have to migrate yourself. With 3.5 be aware that repairs don't work well (see CASSANDRA-12888).
Note: that Materialized Views are probably not best idea to use and has been changed to "experimental" status
i new for use apache cassandra, i have install cassandra and use cqlsh in my laptop
i used to create table using :
create table userpageview( created_at timestamp, hit int, userid int, variantid int, primary key (created_at, hit, userid, variantid) );
and insert several data into table, but when i tried to select using condition for all column (i mean one by one) it's error
maybe my data modelling wrong, maybe anyone can tell me how create data modelling in cassandra
thx
You need to read about partition keys and clustering keys. Cassandra works much differently than relational databases and the types of queries you can do are much more restricted.
Some information to get you started: here and here.
There is one particular table in the system that I actually want to stay unique on a per server basis.
i.e. http://server1.example.com/some_stuff.html and http://server2.example.com/some_stuff.html should store and show data unique to that particular server. If one of the server dies, that table and its data goes with it.
I think CQL does not support table-level replication factors (see available create table options). One alternative is to create a key-space with a replication factor = 1:
CREATE KEYSPACE <ksname>
WITH replication = {'class':'<strategy>' [,'<option>':<val>]};
Example:
To create a keyspace with SimpleStrategy and "replication_factor" option
with a value of "1" you would use this statement:
CREATE KEYSPACE <ksname>
WITH replication = {'class':'SimpleStrategy', 'replication_factor':1};
then all tables created in that key-space will have no replication.
If you would like to have a table for each node, then I think Cassandra does not directly support that. One work-around is to start an additional Cassandra cluster for each node where each cluster only have one node.
I am not sure why you would want to do that, but here is my take on this:
Distribution of the actual your data among the nodes in your Cassandra cluster is determined by the row key.
Just setting the replication factor to 1 will not put all data from one column family/table on 1 node. The data will still be split/distributed according to your row key.
Exactly WHERE your data will be stored is determined by the row key along with the partitioner as documented here. This is an inherent part of a DDBS and there is no easy way to force this.
The only way I can think of to have all the data for one server phisically in one table on one node, is:
use one row key per server and create (very) wide rows, (maybe using composite column keys)
and trick your token selection so that all row key tokens map to the node you are expecting (http://wiki.apache.org/cassandra/Operations#Token_selection)
I'm trying to leverage a specific feature of Apache Cassandra CQL3, which is partition and clustering keys for tables which are created with compact storage option.
For Eg.
CREATE TABLE EMPLOYEE(id uuid, name text, field text, value text, primary key(id, name , field )) with compact storage;
I've created the table via CQL3 and i;m able to insert rows successfully using the Hector API.
But I couldn't find right set of options in the hector api to create the table itself as i require.
To elaborate a little bit more:
In ColumnFamilyDefinition.java i couldnt see an option for setting storage option (as compact storage) and In ColumnDefinition.java, i couldnt find the option to say that this column is part of the Partition and Clustering Keys
Could you please give me an idea of whether i can use Hector for this (i.e. Creating table) or not and if i can do that, what are the options that i need to provide?
If you are not tied to Hector, you could look into the DataStax Java Driver which was created to use CQL3 and Cassandra's binary protocol.
I'm currently evaluating Cassandra for an upcoming project and am trying to get my head around the basics.
I have an issue where when creating a column family via the CQL Shell - the column family is created as usable however it does not appear when I issue a DESCRIBE command with the CLI tool or when looking at the Cluster via DataStax OpsCenter.
I've created the keyspace as such:
CREATE KEYSPACE Testing
WITH replication = {'class': 'SimpleStrategy', 'replication_factor' : 1};
and defined the column family as:
CREATE TABLE SampleTable(
Id int PRIMARY KEY,
Name text,
OtherValue int
);
I can successfully insert and select data from SampleTable however it does not show up with a Describe command or in OpsCenter.
I can create a visible Column Family using the CLI command line, or the API in FluentCassandra but would like to use the CQL approach.
This is day one with Cassandra so I'm sure I'm missing something simple. Any pointers?
Column families created with CQL3 do not show up when using the thrift API. See the following issues for more information:
https://issues.apache.org/jira/browse/CASSANDRA-4377
https://issues.apache.org/jira/browse/CASSANDRA-4924