健哥的数据花园

摘要： /* * get_baserel_parampathinfo * Get the ParamPathInfo for a parameterized path for a base relation, * constructing one if we don't have one already. * * This centralizes estimating the rowcounts for parameterized paths. * We need to cache those to be sure we use the same rowcount for ... 阅读全文

摘要： 看官方文档：http://www.postgresql.org/docs/current/static/sql-prepare.htmlPREPARE creates a prepared statement. A prepared statement is a server-side object that can be used to optimize performance. When the PREPARE statement is executed, the specified statement is parsed, analyzed, and rewritten. When an 阅读全文

摘要： Improve the planner's ability to use nested loops with inner index scans (Tom Lane)The new "parameterized path" mechanism allows inner index scans to use values from relations that are more than one join level up from the scan. This can greatly improve performance in situations where s 阅读全文

摘要： 代码：import java.sql.Connection;import java.sql.DriverManager;import java.sql.PreparedStatement;import java.sql.ResultSet;public class Test02 { public static void main(String argsv[]){ try { Class.forName("org.postgresql.Driver").newInstance(); String url = "jdbc... 阅读全文

摘要： Java 代码，在数据库端，并没有当成 prepared statetment 被处理。C代码通过libpq 访问数据库端，被当成了 prepared statement 处理。也许是因PostgreSQL对JDBC的支持毕竟是后期出现的：下面看代码和运行结果：Java 代码：import java.sql.*; public class Test01 { public static void main(String argsv[]){ try { Class.forName("org.postgresql.Driver").n... 阅读全文

摘要： 代码如下：[root@lex tst]# cat testlibpq.c/* * testlibpq.c * Test the C version of LIBPQ, the POSTGRES frontend library. */#include <stdio.h>#include <stdlib.h>#include "libpq-fe.h"static voidexit_nicely(PGconn *conn){ PQfinish(conn); exit(EXIT_SUCCESS);}intmain(){ int nFields; int i 阅读全文

摘要： 程序：[root@lex tst]# cat testlibpq.c/* * testlibpq.c * Test the C version of LIBPQ, the POSTGRES frontend library. */#include <stdio.h>#include <stdlib.h>#include "libpq-fe.h"static voidexit_nicely(PGconn *conn){ PQfinish(conn); exit(EXIT_SUCCESS);}intmain(){ char *pghost, *pgpor 阅读全文

摘要： http://www.postgresql.org/docs/9.2/static/sql-prepare.htmlPREPARE creates a prepared statement. A prepared statement is a server-side object that can be used to optimize performance. When the PREPARE statement is executed, the specified statement is parsed, analyzed, and rewritten. When an EXECUTE c 阅读全文

摘要： 继续分析/* * final_cost_hashjoin * Final estimate of the cost and result size of a hashjoin path. * * Note: the numbatches estimate is also saved into 'path' for use later * * 'path' is already filled in except for the rows and cost fields and * num_batches * 'workspace' is the r 阅读全文

摘要： 看hash join 里的概念：numbuckets与numbatches：numbuckets是 在内存中，hash表里面，"桶"的个数。numbatches是 如果hash表过大，在内存中放不下，则要分多次进行。voidfinal_cost_hashjoin(PlannerInfo *root, HashPath *path, JoinCostWorkspace *workspace, SpecialJoinInfo *sjinfo, SemiAntiJoinFactors *... 阅读全文