Learn JAVA 20th day, contact exception handling, customize exception

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 ...

Added by ypirc on Wed, 15 May 2019 13:47:55 +0300

PostgreSQL page inspect diagnoses and optimizes the query performance degradation caused by the delay of GIN (inverted) index merging

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 ...

Added by hatching on Wed, 15 May 2019 09:30:25 +0300

InnoDB Engine B+Tree Index Usage and New Features

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 ...

Added by ehhwan on Wed, 15 May 2019 05:12:03 +0300

Competition for Cache Buffers Chain Latch

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 ...

Added by PHP Monkeh on Tue, 14 May 2019 18:13:35 +0300

MySql and Pytnon Interaction

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 ...

Added by jwoo on Tue, 14 May 2019 16:37:38 +0300

PostgreSQL 11.1 trillion tpcb performance test on Aliyun ECS + ESSD + zfs/lvm2 strip + block_size=32K

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 ...

Added by stanleycwb on Tue, 14 May 2019 14:43:51 +0300

Database System Experiment 4: SQL-SELECT Query Operation

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 ...

Added by nalleyp23 on Sun, 12 May 2019 13:43:12 +0300

Optimized case of semi-connection and anti-connection

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 ...

Added by roneill on Sun, 12 May 2019 12:38:52 +0300