Cassandra Query No ratings yet.

Time Series db using cassandra Try it out   cqlsh:demo> create TABLE demo.users3(lastname text, firstname text, time timestamp , primary key(lastname, time)); cqlsh:demo> INSERT INTO users2(lastname, firstname , time ) VALUES ( ‘test1’, ‘testfir’, 164447) USING TTL 20; cqlsh:demo> select firstname FROM demo.users2;   Data Modeling However, in Cassandra, the data access queries • Read More »

bigdata OLTP , OLAP No ratings yet.

row-based vs col based db or format row based –> good for OLTP ( transcation),   e.g: cassendra col based –> good for OLAP (? easy to aggreation etc?), druid Parquet hadoop: big data storage, what is the alternatives? S3 on cloud?   pinot vs cassandra druid If your queries ALWAYS constrain • Read More »

grpc deep drive No ratings yet.

GRPC   client side msg: header, msg, EOS server side msg:  header, msg, msg,  Trailer over http2 keep live? c++ async or sync? , does it provider more performance than sync one? CPU Bound means the rate at which process progresses is limited by the speed of the CPU. A task that • Read More »

bigdata platform with Kubernets or Hadoop No ratings yet.

Hadoop: Hadoop kubernets MapReduce Spark on K8s Flink stream HDFS S3? any better one Resource manager Yarn/Mesos K8s itself   During its evolution phase, Hadoop provided three main functionalities that made it a Big Data-ready solution: a distributed computer mechanism (MapReduce), a robust data storage (HDFS), and a resource manager (YARN/Mesos). But modern technologies now • Read More »

Some notes about An Elegant Puzzle – Systems of Engineering Management No ratings yet.

Some notes: Team size 8 engineers/manager Managers should support six to eight   Documents to avoid interruption Finally, the one thing that I’ve found at companies with very few interruptions and have observed almost nowhere else: really great, consistently available documentation. It’s probably even harder to bootstrap documentation into a non-documenting company than it is • Read More »

Bias vs Variance in ML No ratings yet.

Somehow even wiki seems not clearly explained what it is due to un-cleary math denotion. The video gave us more precision meaning of bias, variance. Expected error of algorithm the goal of the algorithm is to reduce the total error when we do the  prediction/(genelization). Thus we need to calculate the expected error of the • Read More »

mysql transcations No ratings yet.

Generally how to write transaction Begin transaction by issuing the SQL command BEGIN WORK. Issue one or more SQL commands like SELECT, INSERT, UPDATE or DELETE. Check if there is no error and everything is according to your requirement. If there is any error, then issue a ROLLBACK command, otherwise issue a COMMIT command.   how • Read More »

screen tmux cheat sheet No ratings yet.

Screen screen -d -R your_session name //split only the monitor screen ctrl-a ( release the kb ), then press: | for vsplit    —> need this step : ctrl-a, c ( to create a new window, otherwise just blank screen) ctrl-a ( release the kb ), then press: shift s:  for hsplit ctrl-a , tab • Read More »

c++ multi-set/multi-map, set/map and its unordered version No ratings yet.

container name implementation/underlying struct notes/ sample unordered_set  The value of an element is at the same time its key, that identifies it uniquely. hash table unordered_multiset much like unordered_set containers, but allowing different elements to have equivalent values. hash table Internally when an existing value is inserted, the data structure increases its count which is associated with each • Read More »