> Is that just the way it is? yes. Denormalise your model and store the data in a format that supports the read queries you want to run. Cassandra is predicated on the idea that storage is cheap.
For *most* columns cassandra stores the column name and the value and some meta data. Cheers ----------------- Aaron Morton Freelance Cassandra Developer New Zealand @aaronmorton http://www.thelastpickle.com On 15/11/2012, at 4:18 PM, Kevin Burton <rkevinbur...@charter.net> wrote: > In the below example I am thinking that id is the order id. Would there be > considerable duplication if there are other column families/tables that also > are identified or have a key of id? It seems that id potentially could be > duplicated for each column family/table. Is that just the way it is? While > for a small data set this would be no big deal. But for millions or billions > of orders this becomes significant. > > From: aaron morton [mailto:aa...@thelastpickle.com] > Sent: Wednesday, November 14, 2012 6:00 PM > To: user@cassandra.apache.org > Subject: Re: CF metadata syntax for an array > > database a hint that this will be an array? > Things are going to be easier if you stop thinking about arrays :) > > For background > http://www.datastax.com/docs/1.1/dml/using_cql#using-composite-primary-keys > > The first part of the primary key is the storage engine row key. This is the > ring that cassandra uses to identify the row in the cluster. You could think > of this as similar to a Hive partition. But if you have not used Hive I would > not think of it like that. > > The remaining parts are used to prefix the columns in the row. The internally > the columns created have the names > > * value of item_id : "price" > * value of item_id : "title" > > Hope that helps. > > ----------------- > Aaron Morton > Freelance Cassandra Developer > New Zealand > > @aaronmorton > http://www.thelastpickle.com > > On 15/11/2012, at 11:35 AM, Peter Lin <wool...@gmail.com> wrote: > > > it means the column family uses composite key, which gives you > additional capabilities like order by in the where clause > > On Wed, Nov 14, 2012 at 5:27 PM, Kevin Burton <rkevinbur...@charter.net> > wrote: > > I hope I am not bugging you but now what is the purpose of PRIMARY_KEY(id, > item_id)? By expressing the KEY as two values this basically gives the > database a hint that this will be an array? Is there an implicit INDEX on id > and item_id? Thanks again. > > -----Original Message----- > From: aaron morton [mailto:aa...@thelastpickle.com] > Sent: Wednesday, November 14, 2012 4:08 PM > To: user@cassandra.apache.org > Subject: Re: CF metadata syntax for an array > > Like this? > > cqlsh:dev> CREATE TABLE my_orders( > ... id int, > ... item_id int, > ... price decimal, > ... title text, > ... PRIMARY KEY(id, item_id) > ... ); > > cqlsh:dev> insert into my_orders > ... (id, item_id, price, title) > ... values > ... (1, 1, 4, 'this is an example'); > cqlsh:dev> insert into my_orders > ... (id, item_id, price, title) > ... values > ... (1, 2, 8, 'this is another example'); > cqlsh:dev> insert into my_orders > ... (id, item_id, price, title) > ... values > ... (1, 3, 6, 'this is the last example'); > > cqlsh:dev> select * from my_orders where id = 1; id | item_id | price | > title > ----+---------+-------+-------------------------- > 1 | 1 | 4 | this is an example > 1 | 2 | 8 | this is another example > 1 | 3 | 6 | this is the last example > > > > > ----------------- > Aaron Morton > Freelance Cassandra Developer > New Zealand > > @aaronmorton > http://www.thelastpickle.com > > On 15/11/2012, at 10:38 AM, Kevin Burton <rkevinbur...@charter.net> wrote: > > > An array would be a list of groups of items. In my case I want a > list/array of line items. An order has certain characteristics and one of > them is a list of the items that are being ordered. Say ever line item has > an id, price, and description so one such "array" would look like: > > > 1 $4.00 "This is an example" > 2 $8.00 "This is another example" > 3 $6.00 "This is the last example" > > So in this case the array would be the three items listed above. So the > "column" is repeated three times for this order. > > > From: aaron morton [mailto:aa...@thelastpickle.com] > Sent: Wednesday, November 14, 2012 3:05 PM > To: user@cassandra.apache.org > Subject: Re: CF metadata syntax for an array > > In both cases the array is the PRIMARY_KEY. > I'm not sure what you mean by the "array" > > The vector_name and list_name columns are used as "variable names" to > identify a particular vector or list. They are the storage engine "row key". > > > Cheers > > ----------------- > Aaron Morton > Freelance Cassandra Developer > New Zealand > > @aaronmorton > http://www.thelastpickle.com > > On 14/11/2012, at 5:31 PM, Kevin Burton <rkevinbur...@charter.net> wrote: > > > Does the array have to be a KEY? > Sorry I don't understand this question. > > In the samples you give you specify array as > > CREATE COLUMNFAMILY Description ( > PRIMARY_KEY > (vector_name, index), > > Age text, > Gender text, > vector_name text, > index bigint, > ... > > Or > CREATE COLUMNFAMILY Description ( > PRIMARY_KEY > (listr_name, sort_key), > > Age text, > Gender text, > sort_key bigint, > list_name text > .. > > > In both cases the array is the PRIMARY_KEY. In order for an array to work > does the array have to be a KEY? > > > From: aaron morton [mailto:aa...@thelastpickle.com] > Sent: Tuesday, November 13, 2012 10:18 PM > To: user@cassandra.apache.org > Subject: Re: CF metadata syntax for an array > > > Would this syntax be the same for CREATE COLUMNFAMILY (as an aside what is > a 'TABLE' in Cassandra)? > > Yes, CQL 2 uses COLUMN FAMILY or Table and CQL 3 uses TABLE > > http://www.datastax.com/dev/blog/cql3-evolutions > > In other words is this valid: > Does it work ? Is so it's valid. > > Does the array have to be a KEY? > Sorry I don't understand this question. > > Finally, what would be the syntax for inserting data into the CF? > Depends on what you want to do. > Docs are a good starting point > http://www.datastax.com/docs/1.1/references/cql/index > > Cheers > > ----------------- > Aaron Morton > Freelance Developer > @aaronmorton > http://www.thelastpickle.com > > On 14/11/2012, at 2:42 AM, Kevin Burton <rkevinbur...@charter.net> wrote: > > > > Sorry to be so slow but I am just learning CQL. Would this syntax be the > same for CREATE COLUMNFAMILY (as an aside what is a 'TABLE' in Cassandra)? > In other words is this valid: > > > CREATE COLUMNFAMILY Description ( > PRIMARY_KEY > (vector_name, index), > > Age text, > Gender text, > vector_name text, > index bigint, > ... > > Or > CREATE COLUMNFAMILY Description ( > PRIMARY_KEY > (listr_name, sort_key), > > Age text, > Gender text, > sort_key bigint, > list_name text > .. > > > > Does the array have to be a KEY? Finally, what would be the syntax for > inserting data into the CF? > > > Thanks again. > > From: aaron morton [mailto:aa...@thelastpickle.com] > Sent: Tuesday, November 13, 2012 4:09 AM > To: user@cassandra.apache.org > Subject: Re: CF metadata syntax for an array > > While this solves the problem for an array of 'primitive' types. What if I > want an array or collection of an arbitrary type like list<foo>, where foo > is a user defined type? > > Do you mean a custom Cassandra data type that sub classes AbstractType? I > dont think CQL can support those, I may be wrong though. > > > If you mean a basic client side data type you could serialise it and store > as a string or byte buffer in a CQL collection. > > > What are the options to solve this type of array? > ... > > > > arbitrary type like list<foo>, > Do you mean an array such as int[] or do you mean the equivalent of a java > List<T> with functions like remove that actually delete items and from the > list? > > > If it's the former a CQL table such as below would work > > CREATE TABLE vectors ( > vector_name text, > index bigint, > object_property_1 text, > object_property_2 text, > PRIMARY_KEY (vector_name, index) ); > > The problem is, if you delete a element at (vector, index) the remaining > indexes will be off. > > > If it's the later, a List<T>, then it depends a little on what > features you want to support. If you want a sorted list of objects the > table is roughly the same > > CREATE TABLE List ( > list_name text, > sort_key bigint, > object_property_1 text, > object_property_2 text, > PRIMARY_KEY (list_name, sort_key) ); > > Hope that helps. > > ----------------- > Aaron Morton > Freelance Developer > @aaronmorton > http://www.thelastpickle.com > > ----------------- > Aaron Morton > Freelance Developer > @aaronmorton > http://www.thelastpickle.com > > On 13/11/2012, at 9:46 AM, Kevin Burton <rkevinbur...@charter.net> wrote: > > > > > While this solves the problem for an array of 'primitive' types. What if I > want an array or collection of an arbitrary type like list<foo>, where foo > is a user defined type? I am guessing that this cannot be done with > 'collections'. What are the options to solve this type of array? > > > On Nov 12, 2012, at 2:28 PM, aaron morton <aa...@thelastpickle.com> wrote: > > This may help http://www.datastax.com/dev/blog/cql3_collections > > I have gotten as far as feeling a need to understand a 'super-column' > You can happily ignore them. > > > Cheers > > ----------------- > Aaron Morton > Freelance Developer > @aaronmorton > http://www.thelastpickle.com > > On 12/11/2012, at 8:35 PM, Kevin Burton <rkevinbur...@charter.net> wrote: > > > > > I am sorry if this is an FAQ. But I was wondering what the syntax for > describing an array? I have gotten as far as feeling a need to understand a > 'super-column' but I fail after that. Once I have the metadata in place to > describe an array how do I insert data into the array? Get data from the > array? Thank you. > > > > > ----------------- Aaron Morton Freelance Cassandra Developer New Zealand @aaronmorton http://www.thelastpickle.com
