Related
I'm working on designing an application which will enable users to send requests to connect with each other, see their sent or received requests, make notes during their interactions for later reference if connected, and remove users from their contact lists.
In a RDBMS, the schema would be:
table User with column
uid (a unique string for each user)
table Request with columns:
from - user id
to - user id Primary Key (from, to)
created - timestamp
message - string
expiry - timestamp
table Connection with columns:
from - user id
to - user id
Primary Key (from, to)
notes - String
created - timestamp
modified - timestamp
isFavourite - to is a favourite of from user, value 0 or 1
isActive - soft delete, value 0 or 1
pairedConnection - shows whether the connection between to and from was deactivated (the to user removed the from user from its contact list), value 0 or 1
The queries I anticipate to be needed are:
find the sent requests for a user
find the received requests for a user
find all the active contacts of a given user
find all the favourites of a user
find all the users who deleted the given from user from their lists
update the notes taken by a user when meeting another user he is connected with
update user as favourite
mark connection for soft deletion
I'm trying to model this in Cassandra, but feel confused about the keys to choose for max efficiency.
So far, I have the following ideas, and would welcome feedback from more experienced Cassandra users:
create table users(
uid text PRIMARY KEY
);
create table requestsByFrom(
from text,
to text,
message text,
created timestamp,
expiry timestamp,
PRIMARY KEY (from,to)
create table requestsByTo(
from text,
to text,
message text,
created timestamp,
expiry timestamp,
PRIMARY KEY (to,from)
);
create table connections(
from text,
to text,
notes text,
created timestamp,
modified timestamp,
isFavourite boolean,
isActive boolean,
pairedConnection boolean,
PRIMARY KEY (from,to)
);
create table activeConnections(
from text,
to text,
isActive boolean,
PRIMARY KEY (from,isActive)
);
create table favouriteConnections(
from text,
to text,
isFavourite boolean,
PRIMARY KEY (from, isFavourite)
);
create table pairedConnection(
from text,
to text,
pairedConnection boolean,
PRIMARY KEY ((from,to), pairedConnection)
);
Cassandra has a different paradigm to RDBMS, and this is more evident with the way that the data modeling has to be done. You need to keep in mind that denormalization is preferred, and that you'll have repeated data.
The tables definition should be based on the queries to retrieve the data, this is partially stated in the definition of the problem, for instance:
find the sent requests for a user
Taking the initial design of the table requestsByFrom, an alternative will be
CREATE TABLE IF NOT EXISTS requests_sent_by_user(
requester_email TEXT,
recipient_email TEXT,
recipient_name TEXT,
message TEXT,
created TIMESTAMP
PRIMARY KEY (requester_email, recipient_email)
) WITH default_time_to_live = 864000;
Note that from is a restricted keyword, the expiry information can be set with the definition of the default_time_to_live clause (TTL) which will remove the record after the time defined; this value is the amount of seconds after the record is inserted, and the example is 10 days (864,000 seconds).
The primary key is suggested to be the email address, but it can also be an UUID, name is not recommended as there can be multiple persons sharing the same name (like James Smith) or the same person can have multiple ways to write the name (following the example Jim Smith, J. Smith and j smith may refer to the same person).
The name recipient_name is also added as it is most likely that you'll want to display it; any other information that will be displayed/used with the query should be added.
find the received requests for a user
CREATE TABLE IF NOT EXISTS requests_received_by_user(
recipient_email TEXT,
requester_email TEXT,
requester_name TEXT,
message TEXT,
created TIMESTAMP
PRIMARY KEY (recipient_email, requester_email)
) WITH default_time_to_live = 864000;
It will be preferred to add records to requests_sent_by_user and requests_received_by_user at the same time using a batch, which will ensure consistency in the information between both tables, also the TTL (expiration of the data) will be the same.
storing contacts
In the question there are 4 tables of connections: connections, active_connections, favourite_connections, paired_connections, what will be the difference between them? are they going to have different rules/use cases? if that is the case, it makes sense to have them as different tables:
CREATE TABLE IF NOT EXISTS connections(
requester_email TEXT,
recipient_email TEXT,
recipient_name TEXT,
notes TEXT,
created TIMESTAMP,
last_update TIMESTAMP,
is_favourite BOOLEAN,
is_active BOOLEAN,
is_paired BOOLEAN,
PRIMARY KEY (requester_email, recipient_email)
);
CREATE TABLE IF NOT EXISTS active_connections(
requester_email TEXT,
recipient_email TEXT,
recipient_name TEXT,
last_update TIMESTAMP,
PRIMARY KEY (requester_email, recipient_email)
);
CREATE TABLE IF NOT EXISTS favourite_connections(
requester_email TEXT,
recipient_email TEXT,
recipient_name TEXT,
last_update TIMESTAMP,
PRIMARY KEY (requester_email, recipient_email)
);
CREATE TABLE IF NOT EXISTS paired_connections(
requester_email TEXT,
recipient_email TEXT,
recipient_name TEXT,
last_update TIMESTAMP,
PRIMARY KEY (requester_email, recipient_email)
);
Note that the boolean flag is removed, the logic is that if the record exists in active_connections, it will be assumed that it is an active connection.
When a new connection is created, it may have several records in different tables; to bundle all those inserts or updates, it is preferred to use batch
find all the active contacts of a given user
Based on the proposed tables, if the requester's email is test#email.com:
SELECT * FROM active_connections WHERE requester_email = 'test#email.com'
update user as favourite
It will be a batch updating the record in connections and adding the new record to favourite_connections:
BEGIN BATCH
UPDATE connections
SET is_favourite = true, last_update = dateof(now())
WHERE requester_email ='test#email.com'
AND recipient_email = 'john.smith#test.com';
INSERT INTO favourite_connections (
requester_email, recipient_email, recipient_name, last_update
) VALUES (
'test#email.com', 'john.smith#test.com', 'John Smith', dateof(now())
);
APPLY BATCH;
mark connection for soft deletion
The information of the connection can be kept in connections with all the flags disabled, as well as the records removed from active_connections, favourite_connections and paired_connections
BEGIN BATCH
UPDATE connections
SET is_active = false, is_favourite = false,
is_paired = false, last_update = dateof(now())
WHERE requester_email ='test#email.com'
AND recipient_email = 'john.smith#test.com';
DELETE FROM active_connections
WHERE requester_email = 'test#email.com'
AND recipient_email = 'john.smith#test.com';
DELETE FROM favourite_connections
WHERE requester_email = 'test#email.com'
AND recipient_email = 'john.smith#test.com';
DELETE FROM paired_connections
WHERE requester_email = 'test#email.com'
AND recipient_email = 'john.smith#test.com';
APPLY BATCH;
In the process of learning Cassandra and using it on a small pilot project at work. I've got one table that is filtered by 3 fields:
CREATE TABLE webhook (
event_id text,
entity_type text,
entity_operation text,
callback_url text,
create_timestamp timestamp,
webhook_id text,
last_mod_timestamp timestamp,
app_key text,
status_flag int,
PRIMARY KEY ((event_id, entity_type, entity_operation))
);
Then I can pull records like so, which is exactly the query I need for this:
select * from webhook
where event_id = '11E7DEB1B162E780AD3894B2C0AB197A'
and entity_type = 'user'
and entity_operation = 'insert';
However, I have an update query to set the record inactive (soft delete), which would be most convenient by partition key in the same table. Of course, this isn't possible:
update webhook
set status_flag = 0
where webhook_id = '11e8765068f50730ac964b31be21d64e'
An example of why I'd want to do this, is a simple DELETE from an API endpoint:
http://myapi.com/webhooks/11e8765068f50730ac964b31be21d64e
Naturally, if I update based on the composite key, I'd potentially inactivate more records than I intend to.
Seems like my only choice, doing it the "Cassandra Way", is to use two tables; the one I already have and one to track status_flag by webhook_id, so I can update based on that id. I'd then have to select by webhook_id in the first table and disable it there as well? Otherwise, I'd have to force users to pass all the compound key values in the URL of the API's DELETE request.
Simple things you take for granted in relational data, seem to get complex very quickly in Cassandraland. Is this the case or am I making it more complicated than it really is?
You can add webhook to your primary key.
So your table defination becomes somethign like this.
CREATE TABLE webhook (
event_id text,
entity_type text,
entity_operation text,
callback_url text,
create_timestamp timestamp,
webhook_id text,
last_mod_timestamp timestamp,
app_key text,
status_flag int,
PRIMARY KEY ((event_id, entity_type, entity_operation),webhook_id)
Now lets say you insert 2 records.
INSERT INTO dev_cybs_rtd_search.webhook(event_id,entity_type,entity_operation,status_flag,webhook_id) VALUES('11E7DEB1B162E780AD3894B2C0AB197A','user','insert',1,'web_id');
INSERT INTO dev_cybs_rtd_search.webhook(event_id,entity_type,entity_operation,status_flag,webhook_id) VALUES('12313131312313','user','insert',1,'web_id_1');
And you can update like following
update webhook
set status_flag = 0
where webhook_id = 'web_id' AND event_id = '11E7DEB1B162E780AD3894B2C0AB197A' AND entity_type = 'user'
AND entity_operation = 'insert';
It will only update 1 record.
However you have to send all the things defined in your primary key.
I'm trying to build a news feed system using Cassandra, I was thinking of using a fan out approach wherein if a user posts a new post, I'll write a new record in all of his friends' feed table. The table structure looks like:
CREATE TABLE users (
user_name TEXT,
first_name TEXT,
last_name TEXT,
profile_pic TEXT,
PRIMARY KEY (user_name)
);
CREATE TABLE user_feed (
user_name TEXT,
posted_time TIMESTAMP,
post_id UUID,
posted_by TEXT, //posted by username
posted_by_profile_pic TEXT,
post_content TEXT,
PRIMARY KEY ((user_name), posted_time)
) WITH CLUSTERING ORDER BY(posted_time desc);
Now, I can get a feed for a particular user in a single query all fine. What if the user who has posted a feed updates his profile pic. How do I go about updating the data in user_feed table?
You can use batch statements to achieve atomicity at your updates. So in this case you can create a batch with the update on tables users and user_feed using the same user_name partition key:
BEGIN BATCH
UPDATE users SET profile_pic = ? WHERE user_name = ?;
UPDATE user_feed SET posted_by_profile_pic = ? WHERE user_name = ?;
APPLY BATCH;
Take a look at CQL Batch documentation
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
I have gone though this article and here is the schema I have got from it. This is helpful for my application for maintaining statuses of a user, but how can I extend this to maintain one to one chat archive and relations between users, relations mean people belong to specific group for me. I am new to this and need an approach for this.
Requirements :
I want to store messages between user-user in a table.
Whenever a user want to load messages by a user. I want to retrieve them back and send it to user.
I want to retrieve all the messages from different users to the user when user has requested.
And also want to store class of users. I mean for example user1 and user2 belong to "family" user3, user4, user1 belong to friends etc... This group can be custom name given by the user.
This is what I have tried so far:
CREATE TABLE chatarchive (
chat_id uuid PRIMARY KEY,
username text,
body text
)
CREATE TABLE chatseries (
username text,
time timeuuid,
chat_id uuid,
PRIMARY KEY (username, time)
) WITH CLUSTERING ORDER BY (time ASC)
CREATE TABLE chattimeline (
to text,
username text,
time timeuuid,
chat_id uuid,
PRIMARY KEY (username, time)
) WITH CLUSTERING ORDER BY (time ASC)
Below is the schema that I currently have:
CREATE TABLE users (
username text PRIMARY KEY,
password text
)
CREATE TABLE friends (
username text,
friend text,
since timestamp,
PRIMARY KEY (username, friend)
)
CREATE TABLE followers (
username text,
follower text,
since timestamp,
PRIMARY KEY (username, follower)
)
CREATE TABLE tweets (
tweet_id uuid PRIMARY KEY,
username text,
body text
)
CREATE TABLE userline (
username text,
time timeuuid,
tweet_id uuid,
PRIMARY KEY (username, time)
) WITH CLUSTERING ORDER BY (time DESC)
CREATE TABLE timeline (
username text,
time timeuuid,
tweet_id uuid,
PRIMARY KEY (username, time)
) WITH CLUSTERING ORDER BY (time DESC)
With C* you need to store data in the way you'll use it.
So let's see how this would look like for this case:
I want to store messages between user-user in a table.
Whenever a user want to load messages by a user. I want to retrieve them back and send it to user.
CREATE TABLE chat_messages (
message_id uuid,
from_user text,
to_user text,
body text,
class text,
time timeuuid,
PRIMARY KEY ((from_user, to_user), time)
) WITH CLUSTERING ORDER BY (time ASC);
This will allow you to retrieve a timeline of messages between two users. Note that a composite primary key is used so that wide rows are created for each pair of users.
SELECT * FROM chat_messages WHERE from_user = 'mike' AND to_user = 'john' ORDER BY time DESC ;
I want to retrieve all the messages from different users to the user when user has requested.
CREATE INDEX chat_messages_to_user ON chat_messages (to_user);
This allows you to do:
SELECT * FROM chat_messages WHERE to_user = 'john';
And also want to store class of users. I mean for example user1 and user2 belong to "family" user3, user4, user1 belong to friends etc... This group can be custom name given by the user.
CREATE INDEX chat_messages_class ON chat_messages (class);
This will allow you to do:
SELECT * FROM chat_messages WHERE class = 'family';
Note that in this kind of database, DENORMALIZED DATA IS A GOOD PRACTICE. This means that using the name of the class again and again is not a bad practice.
Also note that I haven't used a 'chat_id' nor a 'chats' table. We could easily add this but I feel that your use case didn't require it as it has been put forward. In general, you cannot do joins in C*. So, using a chat id would imply two queries.
EDIT: Secondary indexes are inefficient. A materialised view will be a better implementation with C* 3.0
There is a chat application created by Alan Chandler on github that has the features you request:
MBchat
It uses a 2-phase authentication. First the user is validated in the forums and then, the user is validated on the chat database.
Here's the first validation part of the schema (schema located in inc/user.sql):
BEGIN;
CREATE TABLE users (
uid integer primary key autoincrement NOT NULL,
time bigint DEFAULT (strftime('%s','now')) NOT NULL,
name character varying NOT NULL,
role text NOT NULL DEFAULT 'R', -- A (CEO), L (DIRECTOR), G (DEPT HEAD), H (SPONSOR) R(REGULAR)
cap integer DEFAULT 0 NOT NULL, -- 1 = blind, 2 = committee secretary, 4 = admin, 8 = mod, 16 = speaker 32 = can't whisper( OR of capabilities).
password character varying NOT NULL, -- raw password
rooms character varying, -- a ":" separated list of rooms nos which define which rooms the user can go in
isguest boolean DEFAULT 0 NOT NULL
);
CREATE INDEX userindex ON users(name);
-- Below here you can add the specific users for your set up in the form of INSERT Statements
-- This list is test users to cover the complete range of functions. Note names are converted to lowercase, so only put lowercase names in here
INSERT INTO users(uid,name,role,cap,password,rooms,isguest) VALUES
(1,'alice','A',4,'password','7',0), -- CEO class user alice
(2,'bob','L',3,'password','8',0), -- DIRECTOR class user bob
(3,'carol','G',2,'password','7:8:9',0), -- DEPT HEAD class user carol
And here's the second validation part of the schema (schema located in data/chat.sql):
CREATE TABLE users (
uid integer primary key NOT NULL,
time bigint DEFAULT (strftime('%s','now')) NOT NULL,
name character varying NOT NULL,
role char(1) NOT NULL default 'R',
rid integer NOT NULL default 0,
mod char(1) NOT NULL default 'N',
question character varying,
private integer NOT NULL default 0,
cap integer NOT NULL default 0,
rooms character_varying
);
The following is the schema of the chat rooms you can see the user classes and the examples of it:
CREATE TABLE rooms (
rid integer primary key NOT NULL,
name varchar(30) NOT NULL,
type integer NOT NULL -- 0 = Open, 1 = meeting, 2 = guests can't speak, 3 moderated, 4 members(adult) only, 5 guests(child) only, 6 creaky door
) ;
INSERT INTO rooms (rid, name, type) VALUES
(1, 'The Forum', 0),
(2, 'Operations Gallery', 2), -- Guests Can't Speak
(3, 'Dungeon Club', 6), -- creaky door
(4, 'Auditorium', 3), -- Moderated Room
(5, 'Blue Room', 4), -- Members Only (in Melinda's Backups this is Adults)
(6, 'Green Room', 5), -- Guest Only (in Melinda's Backups this is Juveniles AKA Baby Backups)
(7, 'The Board Room', 1), -- Various meeting rooms - need to be on users room list
The users have another table to indicate the participation of the conversation:
CREATE table wid_sequence ( value integer);
INSERT INTO wid_sequence (value) VALUES (1);
CREATE TABLE participant (
uid integer NOT NULL REFERENCES users (uid) ON DELETE CASCADE ON UPDATE CASCADE,
wid integer NOT NULL,
primary key (uid,wid)
);
And the archives are recorded as follows:
CREATE TABLE chat_log (
lid integer primary key,
time bigint DEFAULT (strftime('%s','now')) NOT NULL,
uid integer NOT NULL REFERENCES user (uid) ON DELETE CASCADE ON UPDATE CASCADE,
name character varying NOT NULL,
role char(1) NOT NULL,
rid integer NOT NULL,
type char(2) NOT NULL,
text character varying
);
Edit: However this type of data modeling is not very suitable for Cassandra. Because, in Cassandra your data does not fit on one machine so joins are not available. So, in Cassandra denormalizing data is the practical choice. Check below for the denormalized version of chat_log table:
CREATE TABLE chat_log (
lid uuid,
time timestamp,
sender text NOT NULL,
receiver text NOT NULL,
room text NOT NULL,
sender_role varchar NOT NULL,
receiver_role varchar NOT NULL,
rid decimal NOT NULL,
status varchar NOT NULL,
message text,
PRIMARY KEY (sender, receiver, room)
-- PRIMARY KEY (sender, receiver) if you don't want the messages to be separated by the rooms
) WITH CLUSTERING ORDER BY (time ASC);
Now in order to retrieve data you'd use the following queries:
Whenever a user want to load messages by a user. I want to retrieve them back and send it to user.
SELECT * FROM chat_log WHERE sender = 'bob' ORDER BY time ASC
I want to retrieve all the messages from different users to the user when user has requested.
SELECT * FROM chat_log WHERE receiver = 'alice' ORDER BY time ASC
I want to store and retrieve class of users.
SELECT * FROM chat_log WHERE sender_role = 'A' ORDER BY time ASC -- messages sent by CEOs
SELECT * FROM chat_log WHERE receiver_role = 'A' ORDER BY time ASC -- messages received by CEOs
After modeling the data. You'd need to create indexes for quick and efficient querying as follows:
For retrieving all messages from different users to the user efficiently
CREATE INDEX chat_log_uid ON chat_log (sender);
CREATE INDEX chat_log_uid ON chat_log (receiver);
For retrieving all messages from user classes efficiently
CREATE INDEX chat_log_class ON chat_log (sender_role);
CREATE INDEX chat_log_class ON chat_log (receiver_role);
I believe these examples will give you the approach you need.
If you'd like to learn more about Cassandra data modeling you can check down below:
Cassandra Data Modeling Best Practices, Part 1
Cassandra Data Modeling Best Practices, Part 2
Cassandra Data Modeling Best Practices Slide
Data Modeling Example