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Articles by Mithlesh Upadhyay
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Node in Apache Cassandra
Apache Cassandra is an open-source NoSQL database written in Java, designed for high availability with no single point of failure. Nodes are the fundamental building blocks of Cassandra's distributed architecture, forming a peer-to-peer ring structure. Node in Cassandra Each node holds actual data along with metadata (location, data center, keyspaces, tables, schema). Nodes form a ring where every node is equal − no master/slave hierarchy. Data is distributed across nodes using a partitioner, and replicas are stored on multiple nodes for fault tolerance. ...
Read MoreNO-UNDO REDO Recovery Based on Deferred Update
In deferred update recovery, actual database modifications on disk are postponed until a transaction commits. Updates are recorded only in the log and cache buffers during execution. If a transaction fails before commit, the database on disk remains unaffected − hence NO-UNDO. Only REDO is needed for committed transactions whose changes haven't been written to disk. Deferred Update Protocol A transaction cannot modify the database on disk until it reaches its commit point. All REDO log entries must be force-written to disk before commit (Write-Ahead Logging). Only REDO log entries (new values/AFIM) are needed − no UNDO ...
Read MoreNew Storage Systems
Modern storage systems are designed to handle large data volumes with reliability, scalability, and cost-effectiveness. The three significant developments are SAN, NAS, and iSCSI. SAN Fibre Channel Block-level access NAS Ethernet / LAN File-level access iSCSI SCSI over IP Block-level over Ethernet Storage Area Networks (SAN) SAN is a high-speed dedicated network of storage devices configured as nodes, allowing flexible attachment and detachment from servers. SANs use Fibre ...
Read MoreNetwork Attached Storage in DBMS
Network Attached Storage (NAS) is a dedicated storage device connected to a network that allows multiple clients to store and access files. In DBMS, NAS serves as a storage solution for database files, backups, and shared data without requiring a full server. NAS Storage Device LAN (Ethernet) DB Server Web Server ...
Read MoreNested Queries in SQL
A nested query (subquery) is a query placed inside another query. The inner query executes first and its result is used by the outer query for more complex data retrieval. Syntax SELECT column1, column2 FROM table1 WHERE column1 IN ( SELECT column1 FROM table2 WHERE condition ); Types of Nested Queries Non-Correlated Inner runs independently Result passed to outer Operators: IN, NOT IN, ALL, ANY ...
Read MoreMySQL PARTITION BY Clause
The PARTITION BY clause in MySQL groups rows into separate partitions (windows) for use with window functions like RANK(), DENSE_RANK(), LEAD(), and LAG(). It must always be used inside an OVER() clause. If omitted, the entire table is treated as a single partition. Syntax window_function(expression) OVER (PARTITION BY column_name [ORDER BY column_name] [frame_clause]) Example Consider a Hacker table ? CREATE TABLE Hacker ( h_id INT, h_name VARCHAR(50), challenge_id INT, score INT ); INSERT INTO Hacker ...
Read MoreMultiversion Timestamp Ordering
Multiversion Timestamp Ordering (MVTO) is a concurrency control technique that maintains multiple versions of each data item. Each version has a unique timestamp, and transactions access the appropriate version based on their own timestamp, preventing conflicts and deadlocks. Components Each version Xi of a data item maintains − Value − The data content of that version. Read_TS(Xi) − Largest timestamp of any transaction that successfully read Xi. Write_TS(Xi) − Timestamp of the transaction that created Xi. How MVTO Works ...
Read MoreMultiple Granularity Locking in DBMS
Multiple granularity locking provides different levels of locks for different database objects − from the entire database down to individual records. This maximizes concurrency while maintaining consistency. Granularity Hierarchy Database Area 1 Area 2 File 1 File 2 File 3 File 4 R1 ...
Read MoreMultilevel Indexes
In RDBMS, indexes are data structures that speed up data retrieval by reducing disk accesses. As databases grow, single-level indexes become too large for main memory. Multilevel indexes solve this by dividing the index into a hierarchy of smaller, manageable blocks. Index Components Search Key Sorted primary/candidate key points to Data Reference Pointer to disk ...
Read MoreMulti-tier architecture of Data Warehouse
A data warehouse is a central repository that consolidates data from multiple sources into a format optimized for analysis and decision-making. To handle the complexity and volume of data efficiently, data warehouses use a multi-tier architecture where each layer performs a specific function. Multi-tier Architecture Layers Data Sources DBs, Files, External APIs ...
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