Technology Questions

At the time of updating the data warehouse, a lookup table is used. When placed on the fact table or warehouse based upon the primary key of the target, the update is takes place only by allowing new records or updated records depending upon the condition of lookup.

The materialized views are aggregate tables. It contains summarized data. For example, to generate sales reports on weekly or monthly or yearly basis instead of daily basis of an application, the date values are aggregated into week values, week values are aggregated into month values and month values into year values. To perform this process aggregate function is used.

Delete command removes the rows from a table based on the condition that we provide with a WHERE clause. Truncate will actually remove all the rows from a table and there will be no data in the table after we run the truncate command.

TRUNCATE:

- TRUNCATE is faster and uses fewer system and transaction log resources than DELETE.

- TRUNCATE removes the data by deallocating the data pages used to store the table's data, and only the page deallocations are recorded in the transaction log.

- TRUNCATE removes all rows from a table, but the table structure, its columns, constraints, indexes and so on, remains. The counter used by an identity for new rows is reset to the seed for the column.

- You cannot use TRUNCATE TABLE on a table referenced by a FOREIGN KEY constraint. Because TRUNCATE TABLE is not logged, it cannot activate a trigger.

- TRUNCATE cannot be rolled back.

- TRUNCATE is DDL Command.

- TRUNCATE Resets identity of the table

DELETE:

- DELETE removes rows one at a time and records an entry in the transaction log for each deleted row.

- If you want to retain the identity counter, use DELETE instead. If you want to remove table definition and its data, use the DROP TABLE statement.

- DELETE Can be used with or without a WHERE clause

- DELETE Activates Triggers.

- DELETE can be rolled back.

- DELETE is DML Command.

- DELETE does not reset identity of the table.

Note: DELETE and TRUNCATE both can be rolled back when surrounded by TRANSACTION if the current session is not closed. If TRUNCATE is written in Query Editor surrounded by TRANSACTION and if session is closed, it can not be rolled back but DELETE can be rolled back.

-  The process of having a copy of redo log files is called mirroring.
-  It is done by creating group of log files together. This ensures that LGWR automatically writes them to all the members of the current on-line redo log group.
-  In case a group fails, the database automatically switches over to the next group. It diminishes the performance.

Aynchronous and Event Driven - All APIs of Node.js library area unit aynchronous that's non-blocking. It basically means that a Node.js based mostly server not waits for a API to return information. Server moves to next API when calling it and a notification mechanism of Events of Node.js helps server to induce response from the previous API decision.

Very Fast - Node.js library is very fast in execution of code.

Single Threaded but highly Scalable - Node.js uses a single threaded model with event looping. Node.js uses a single threaded program and same program can services much larger number of requests than traditional server like open source.

No Buffering - Node.js applications never buffer any data. These applications simply output the data in faster.

The Java programming language provides a system-level thread to track memory allocation.

Garbage collection has the following characteristics:

• Checks for and frees memory no longer needed

• Is done automatically

• Can vary dramatically across JVM implementations

Standard modules contain variables, procedures and functions that are accessible anywhere within the project. A class module contains properties and events, and is made accessible only by objects that were created as an instance of that class.

A Monitor defines a lock and condition variables for managing concurrent access to shared data. The monitor uses the lock to ensure that only a single thread inactive in the monitor code at any time.

A monitor allows only one thread to lock an object at once.

All the above listed are debugging windows in .NET