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General database role privilege handling in SQL Server   Recently, we have been doing database privilege cleanup with colleagues, mainly by deleting some accounts, removing the larger privileges of some accounts, etc. For example, some have db_owner privileges, we remove the database role db_owner of the accounts and grant the minimum required ...

1.java.lang.NullPointerException (Runtime Exception) is a runtime exception that the compiler cannot predict, such as when you define a Reference variable String a, but you did not instantiate the variable with the new keyword. There are two solutions to this null pointer exception, because you call this a's method againif(null!=a) this variabl ...

Label PostgreSQL, brin index, gin index, merge delay, gin_pending_list_limit, query performance degradation background GIN index is an inverted index of PostgreSQL database with multi-value type. A record may involve KEY in multiple GIN indexes. So if index is merged in real time when writing, IO will increase sharply and RT will increase in ...

We've already talked about it Principle and algorithm of MySQL InnoDB index Here's how to manage and use B+tree indexes and some new features. Management of B+Tree Index The basic indexes we use in the InnoDB engine are B+tree indexes. Create and delete indexes It can be created and deleted in two ways: # Mode 1: alter table, in which case bot ...

Oracle Kernel Technology Disclosure_Lv Haibo's Learning Notes When Cache Buffers Chain(CBC) Latch is competing, there are two main situations: 1. Multiple incompatible processes apply for the same CBC Latch to access different Buffer Headers (BH) of different chain lists protected by this CBC Latch, which is called hot chain c ...

Introducing modules into files import Mysqldb Connection object Used to establish connection with database Create object: call connect() method Conn = connect (parameter list) Parameter host: connected mysql host, if the local host is'localhost' Parametric port: The port of the mysql host connected by default is 330 ...

Label PostgreSQL, pgbench, tpcb, tpcc, tpch, lvm2, zfs, bands background Several recent PostgreSQL OLTP and OLAP tests: PostgreSQL 11 tpcc Test (103,000 tpmC on ECS) - use sysbench-tpcc by Percona-Lab (TPC-H test SF=10,SF=200) PostgreSQL 11 vs 10 vs Deepgreen PostgreSQL 10 billion tpcb performance on ECS PostgreSQL on Aliyun ECS + ESSD - 100 ...

Database System Experiment 4: SQL Language-SELECT Query Operation Database System Experiment 4: SQL Language-SELECT Query Operation Experimental environment Experimental content Steps and processes First create the jxgl database for testing by following SQL statements Use SQL statements to express the following queries ...

Let's first understand some concepts: Semi-join: Two tables are associated, returning only matched data and only one table. Semi-join generally refers to the occurrence of IN and EXISTS in sub-queries. Anti-join: A connection between two tables that returns only the data of the main table and only the data that is not associa ...