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From Subroto Barua <sbarua...@yahoo.com.INVALID>
Subject Re: Question: Behavior of inserting a list multiple times with same timestamp
Date Tue, 20 Jun 2017 04:09:19 GMT
here is the response from Datastax support/dev:


In a list each item is its own cell. Append adds a new cell sorted at basically "current server
time uuid" prepend adds at "-current server time uuid". User supplied time stamps are used
for the cell timestamp when specified.

Inserting the entire list deletes and then inserts

Reading reads out the entire list
Positional access reads the entire list and gets/puts at the spot specified

Basically, lists are not idempotent


On Monday, June 19, 2017, 6:55:40 AM PDT, Thakrar, Jayesh <jthakrar@conversantmedia.com>
wrote:

Subroto,

Cassandra docs say otherwise.

Writing list data is accomplished with a JSON-style syntax. To write a record using INSERT,
specify the entire list as a JSON array. Note: An INSERT will always replace the entire list.

Maybe you can elaborate/shed some more light?

Thanks,
Jayesh


Lists

A list is a typed collection of non-unique values where elements are ordered by there position
in the list. To create a column of type list, use the list keyword suffixed with the value
type enclosed in angle brackets. For example:

CREATE TABLE plays (
    id text PRIMARY KEY,
    game text,
    players int,
    scores list<int>
)
Do note that as explained below, lists have some limitations and performance considerations
to take into account, and it is advised to prefer sets over lists when this is possible.

Writing list data is accomplished with a JSON-style syntax. To write a record using INSERT,
specify the entire list as a JSON array. Note: An INSERT will always replace the entire list.

INSERT INTO plays (id, game, players, scores)
          VALUES ('123-afde', 'quake', 3, [17, 4, 2]);
Adding (appending or prepending) values to a list can be accomplished by adding a new JSON-style
array to an existing list column.

UPDATE plays SET players = 5, scores = scores + [ 14, 21 ] WHERE id = '123-afde';
UPDATE plays SET players = 5, scores = [ 12 ] + scores WHERE id = '123-afde';
It should be noted that append and prepend are not idempotent operations. This means that
if during an append or a prepend the operation timeout, it is not always safe to retry the
operation (as this could result in the record appended or prepended twice).

Lists also provides the following operation: setting an element by its position in the list,
removing an element by its position in the list and remove all the occurrence of a given value
in the list. However, and contrarily to all the other collection operations, these three operations
induce an internal read before the update, and will thus typically have slower performance
characteristics. Those operations have the following syntax:

UPDATE plays SET scores[1] = 7 WHERE id = '123-afde';                // sets the 2nd
element of scores to 7 (raises an error is scores has less than 2 elements)
DELETE scores[1] FROM plays WHERE id = '123-afde';                  // deletes the
2nd element of scores (raises an error is scores has less than 2 elements)
UPDATE plays SET scores = scores - [ 12, 21 ] WHERE id = '123-afde'; // removes all occurrences
of 12 and 21 from scores
As with maps, TTLs if used only apply to the newly inserted/updated values.



On 6/19/17, 1:12 AM, "Subroto Barua" <sbarua116@yahoo.com.INVALID> wrote:

    This is an expected behavior.
    
    We learned this issue/feature at the current site (we use Dse 5.08)
    
    Subroto 
    
    > On Jun 18, 2017, at 10:29 PM, Zhongxiang Zheng <zzheng@yahoo-corp.jp> wrote:
    > 
    > Hi all,
    > 
    > I have a question about a behavior when insert a list with specifying timestamp.
    > 
    > It is documented that "An INSERT will always replace the entire list."
    > https://github.com/apache/cassandra/blob/trunk/doc/cql3/CQL.textile#lists
    > 
    > However, When a list is inserted multiple times using same timestamp,
    > it will not be replaced, but will be added as follows.
    > 
    > cqlsh> CREATE TABLE test.test (k int PRIMARY KEY , v list<int>);   
                                                           
                                                           
                                        
    > cqlsh> INSERT INTO test.test (k , v ) VALUES ( 1 ,[1]) USING TIMESTAMP 1000
;                                                           
                                                           
                              
    > cqlsh> INSERT INTO test.test (k , v ) VALUES ( 1 ,[1]) USING TIMESTAMP 1000
;
    > cqlsh> SELECT * FROM test.test ;
    > 
    > k | v
    > ---+--------
    > 1 | [1, 1]
    > 
    > I confirmed this behavior is reproduced in 3.0.13 and 3.10.
    > I'd like to ask whether this behavior is a expected behavior or a bug?
    > 
    > In our use case, CQL statements with same values and timestamp will be issued multiple
times
    > to retry inserting under the assumption that insert is idempotent.
    > So, I expect that the entire list will be replace even if insert a list multiple
times with same timestamp.
    > 
    > Thanks,
    > 
    > Zhongxiang
    > 
    > 
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