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PostgreSQL interview questions

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Question
What is Multi version concurrency control?
Answer
Multi version concurrency control or MVCC is used to avoid unnecessary locking of the database. This removes the time lag for the user to log into his database. This feature or time lag occurs when someone else is accessing the content. All the transactions are kept as a record.
Question
What is a sequence?
Answer
A sequence is a special kind of database object designed for generating unique numeric identifiers. It is typically used to generate artificial primary keys. Sequences are similar, but not identical, to the AUTO_INCREMENT concept in MySQL.

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Question
Is possible to create a shared-storage PostgreSQL server cluster?
Answer
PostgreSQL does not support clustering using shared storage on a SAN, SCSI backplane, iSCSI volume, or other shared media. Such "RAC-style" clustering isn't supported. Only replication-based clustering is currently supported.
Question
What are indices in PostgreSQL?
Answer
There are built in functions such as B-tree, hash table, and GIST indices can be used or users can define their own indices. PostgreSQL can scan the index backwards. An expression index can be created with the addition of a WHERE clause. Partial index created with addition of WHERE clause.
Question
What are string constants in PostgreSQL?
Answer
String constants contain a sequence of characters bound by single quotes. This feature is used during the insertion of a character or passing a character to database objects. PostgreSQL allows the usage of single quotes but embedded by a C style backslash. This feature is important in parsing data.

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