I have a table with schema below :
create table xx(
bucket_id int,
like_count int,
photo_id int,
username text,
PRIMARY KEY(bucket_id,like_count,photo_id)
) WITH CLUSTERING ORDER BY (like_count DESC)
Here i can fetch all records in in descending order of like_count. But i need to update like_count at some point in my app, which i am not able to do because its part of primary key.
If i remove it from primary key, i can not get sorted results based on like_count. What would be correct way to tackle this problem in cassandra?
I am afraid Cassandra is not a good fit for dealing with mutable orders. (Consider Redis Sorted Sets instead)
With that said, you can actually achieve this using CAS-like semantics (compare-and-set) and light-weight transactions which will make your update around 20x slower.
You will also need an additional table that will serve as a lookup for current like_count per bucket_id/photo_id.
create table yy (
bucket_id int,
photo_id int,
like_count int,
PRIMARY KEY((bucket_id,photo_id))
)
Then do a light-weight-transactional delete from xx followed (if success) by an re-insert into xx and update to yy:
Some pseudo code:
//CAS loop (supposedly in a function of args: bucket_id, photo_id, username, new_score)
for (;;) {
//read current score (the assumption here is that the bucket_id/photo_id entry already exists in both xx and yy)
ResultSet rs1 = select like_count from yy where bucket_id = ? and photo_id = ?
int old_score = rs1.one().getInt(0)
//same score don't do anything
if (new_score == old_score) break;
//attempt to delete using light-weight transaction (note usage of IF EXISTS)
ResultSet r2 = delete from xx where bucket_id = ? and photo_id = ? and like_count = old_score IF EXISTS
if (rs2.one().getBool(0)) {
//if delete was successful, reinsert with the new score
insert bucket_id, photo_id, photo_id, username, like_count into xx values (?, ?, ?, new_score)
//update lookup table
update yy set like_count = new_score where bucket_id = ? and photo_id = ?
//we are done!
break;
}
//delete was not successful, someone already updated the score
//try again in a next CAS iteration
}
Remove like_count from PRIMARY KEY definition and perform sorting on the application. If this change happens very rarely on few keys you can think to remove the whole entry and rewrite it with updated value but I don't recommend this solution.
HTH,
Carlo
Related
I have Following Data Model :-
campaigns {
id int PRIMARY KEY,
scheduletime text,
SchduleStartdate text,
SchduleEndDate text,
enable boolean,
actionFlag boolean,
.... etc
}
Here i need to fetch the data basing on start date and end data with out ALLOW FILTERING .
I got more suggestions to re-design schema to full fill the requirement But i cannot filter the data basing on id since i need the data in b/w the dates .
Some one give me a good suggestion to full fill this scenario to execute Following Query :-
select * from campaings WHERE startdate='XXX' AND endDate='XXX' ; // With out Allow Filtering thing
CREATE TABLE campaigns (
SchduleStartdate text,
SchduleEndDate text,
id int,
scheduletime text,
enable boolean,
PRIMARY KEY ((SchduleStartdate, SchduleEndDate),id));
You can make the below queries to the table,
slect * from campaigns where SchduleStartdate = 'xxx' and SchduleEndDate = 'xx'; -- to get the answer to above question.
slect * from campaigns where SchduleStartdate = 'xxx' and SchduleEndDate = 'xx' and id = 1; -- if you want to filter the data again for specific ids
Here the SchduleStartdate and SchduleEndDate is used as the Partition Key and the ID is used as the Clustering key to make sure the entries are unique.
By this way, you can filter based on start, end and then id if needed.
One downside with this will be if you only need to filter by id that wont be possible as you need to first restrict the partition keys.
As a Cassandra novice, I have a CQL design question. I want to re-use a concept which I've build before using RDBMS systems, to create history for customerData. The customer himself will only see the latest version, so that should be the fastest, but queries on whole history can be performed.
My suggested entity properties:
customerId text,
validFromDate date,
validUntilDate date,
customerData text
First save of customerData just INSERTs customerData with validFromDate=NOW and validUntilDate=31-12-9999
Subsequent saves of customerData changes the last record - setting validUntilDate=NOW - and INSERT new customerData with validFromDate=NOW and validUntilDate=31-12-9999
Result:
This way a query of (customerId, validUntilDate)=(id,31-12-9999) will give last saved version.
Query on (customerId) will give all history.
To query customerData at certain time t just use query with validFromDate < t < validUntilDate
My guess is PARTITION_KEY = customerId and CLUSTER_KEY can be validFromDate. Or use PRIMARY KEY = customerId. Or I could create two tables, one for fast querying of lastest version (has no history), and another for historical analyses.
How do you design this in CQL-way? I think I'm thinking too much RDBMish.
Use change timestamp as CLUSTERING KEY with DESC order, e.g
CREATE TABLE customer_data_versions (
id text,
change_time timestamp,
name text,
PRIMARY KEY (id, change_time)
) WITH CLUSTERING ORDER BY ( change_time DESC );
It will allow you to store data versions per customer id in descending order.
Insert two versions for the same id:
INSERT INTO customer_data_versions (id, change_time, name) VALUES ('id1', totimestamp(now()),'John');
INSERT INTO customer_data_versions (id, change_time, name) VALUES ('id1', totimestamp(now()),'John Doe');
Get last saved version:
SELECT * FROM customer_data_versions WHERE id='id1' LIMIT 1;
Get all versions for the id:
SELECT * FROM customer_data_versions WHERE id='id1';
Get versions between dates:
SELECT * FROM customer_data_versions WHERE id='id1' AND change_time <= before_date AND change_time >= after_date;
Please note, there are some limits for partition size (how much versions you will be able to store per customer id):
Cells in a partition: ~2 billion (231); single column value size: 2 GB ( 1 MB is recommended)
my aim is to get the msgAddDate based on below query :
select max(msgAddDate)
from sampletable
where reportid = 1 and objectType = 'loan' and msgProcessed = 1;
Design 1 :
here the reportid, objectType and msgProcessed may not be unique. To add the uniqueness I have added msgAddDate and msgProcessedDate (an additional unique value).
I use this design because I don't perform range query.
Create table sampletable ( reportid INT,
objectType TEXT,
msgAddDate TIMESTAMP,
msgProcessed INT,
msgProcessedDate TIMESTAMP,
PRIMARY KEY ((reportid ,msgProcessed,objectType,msgAddDate,msgProcessedDate));
Design 2 :
create table sampletable (
reportid INT,
objectType TEXT,
msgAddDate TIMESTAMP,
msgProcessed INT,
msgProcessedDate TIMESTAMP,
PRIMARY KEY ((reportid ,msgProcessed,objectType),msgAddDate, msgProcessedDate))
);
Please advice which one to use and what will be the pros and cons between two based on performance.
Design 2 is the one you want.
In Design 1, the whole primary key is the partition key. Which means you need to provide all the attributes (which are: reportid, msgProcessed, objectType, msgAddDate, msgProcessedDate) to be able to query your data with a SELECT statement (which wouldn't be useful as you would not retrieve any additional attributes than the one you already provided in the WHERE statemenent)
In Design 2, your partition key is reportid ,msgProcessed,objectType which are the three attributes you want to query by. Great. msgAddDate is the first clustering column, which will be automatically sorted for you. So you don't even need to run a max since it is sorted. All you need to do is use LIMIT 1:
SELECT msgAddDate FROM sampletable WHERE reportid = 1 and objectType = 'loan' and msgProcessed = 1 LIMIT 1;
Of course, make sure to define a DESC sorted order on msgAddDate (I think by default it is ascending...)
Hope it helps!
SELECT count(*) FROM device_stats
WHERE orgid = 'XYZ'
AND regionid = 'NY'
AND campusid = 'C1'
AND buildingid = 'C1'
AND floorid = '2'
AND year = 2017;
The above CQL query returns correct result - 32032, in CQL Shell
But when I run the same query using QueryBuilder Java API , I see the count as 0
BuiltStatement summaryQuery = QueryBuilder.select()
.countAll()
.from("device_stats")
.where(eq("orgid", "XYZ"))
.and(eq("regionid", "NY"))
.and(eq("campusid", "C1"))
.and(eq("buildingid", "C1"))
.and(eq("floorid", "2"))
.and(eq("year", "2017"));
try {
ResultSetFuture tagSummaryResults = session.executeAsync(tagSummaryQuery);
tagSummaryResults.getUninterruptibly().all().stream().forEach(result -> {
System.out.println(" totalCount > "+result.getLong(0));
});
I have only 20 partitions and 32032 rows per partition.
What could be the reason QueryBuilder not executing the query correctly ?
Schema :
CREATE TABLE device_stats (
orgid text,
regionid text,
campusid text,
buildingid text,
floorid text,
year int,
endofwindow timestamp,
categoryid timeuuid,
devicestats map<text,bigint>,
PRIMARY KEY ((orgid, regionid, campusid, buildingid, floorid,year),endofwindow,categoryid)
) WITH CLUSTERING ORDER BY (endofwindow DESC,categoryid ASC);
// Using the keys function to index the map keys
CREATE INDEX ON device_stats (keys(devicestats));
I am using cassandra 3.10 and com.datastax.cassandra:cassandra-driver-core:3.1.4
Moving my comment to an answer since that seems to solve the original problem:
Changing .and(eq("year", "2017")) to .and(eq("year", 2017)) solves the issue since year is an int and not a text.
Folks,
I would like to solve the following with one table in Cassandra. Said service tracks when users open an asset. On subsequent events to the same asset, we simply over-write the accessDate.
example record:
{ userId: "string", assetId: "string", accessDate: unixTimestamp }
With this said, we need to fulfill the following access requirements (each requirement has its own bulletpoint for readability):
Be able to return all assets a user has opened, and at what time.
This is easy to achieve, table could look like:
CREATE TABLE user_assets_tracker (
userId uuid,
accessDate timestamp,
assetId uuid,
PRIMARY KEY (userid, accessDate, assetId)
);
This allows us to query for all assets, and when each was last accessed.
SELECT *
FROM user_assets_tracker
WHERE userId = 522b1fe2-2e36-4cef-a667-cd4237d08b89
ORDER BY accessDate DESC;
>
Dandy. Now the harder bits, which I am unsure about, was hoping you folks could chime in:
Show me all the assets user added in the past 30 days.
Naturally the LIMIT here is not what we need. Also, we may need to have 2 tables to achieve this.
SELECT *
FROM user_assets_tracker
WHERE userid = 522b1fe2-2e36-4cef-a667-cd4237d08b89
ORDER BY accessDate DESC;
LIMIT 10; ?????
Show me the last accessed item for the user. I think this one is easier, the LIMIT 1 solves that.
This is probably straight forward, with this schema:
CREATE TABLE user_assets_tracker (
userId uuid,
accessDate timestamp,
assetId uuid,
PRIMARY KEY (userid, accessDate, assetId)
);
SELECT *
FROM user_assets_tracker
WHERE userid = 522b1fe2-2e36-4cef-a667-cd4237d08b89
ORDER BY accessDate DESC;
LIMIT 1;
Retrieve the full record for a particular userId + assetId
Since accessDate comes before assetId in our schema, I am not sure how to do this as well. Another table?
Thanks!!
PS It seems that SASI Index could be the solution
Though you are always selecting assetid orderby accessDate desc.
Define your schema with order by accessDate desc
CREATE TABLE user_assets_tracker (
userid uuid,
accessdate timestamp,
assetid uuid,
PRIMARY KEY (userid, accessdate, assetid)
) WITH CLUSTERING ORDER BY (accessdate DESC, assetid ASC);
Now you don't need to specify order by accessDate desc every time. it will by default order your data by accessDate desc
Show me all the assets user added in the past 30 days.
First get timestamp of 30 day ago.
Let's current timestamp of 30 day ago is : 2017-02-05 12:00:00+0000
Now you can query :
SELECT * FROM user_assets_tracker WHERE userid = 522b1fe2-2e36-4cef-a667-cd4237d08b89 AND accessdate >= '2017-02-05 12:00:00+0000'
Retrieve the full record for a particular userId + assetId
If you are using Cassandra 3.0 or above you can use Materialized Views
CREATE a Materialized View :
CREATE MATERIALIZED VIEW user_assets AS
SELECT *
FROM user_assets_tracker
WHERE userid IS NOT NULL AND assetid IS NOT NULL AND accessdate IS NOT NULL
PRIMARY KEY (userid, assetid, accessdate);
Now if you want to get all data with userid and assetid, here is the query
SELECT * FROM user_assets WHERE userid = 522b1fe2-2e36-4cef-a667-cd4237d08b89 AND assetid = 1d45e6c2-02a1-11e7-aac5-b9ab92bee74c;
Here is another thing, if huge data is inserted into a single user, you should add time bucket with userid as partition key.For more check the answer https://stackoverflow.com/a/41857183/2320144