LightDB 23.3 通过GUC参数控制commit fetch

参数控制commit fetch"/>

LightDB 23.3 通过GUC参数控制commit fetch

背景

commit游标提交之后，可以继续使用fetch进行结果集的操作。commit和fetch结合使用功能开发时不考虑分布式。后续，又对分布式进行了测试，发现持有portal后，代码中会对querydesc进行非空判断。当querydesc为空时，LightDB数据库崩溃。修改成对querydesc作非空判断之后，又会导致之前使用一个全局变量接收portal的方案失败。现在一个sql执行完，portal就会释放掉。在事务中调用打开游标的函数， 由于portal被释放，打开的游标就不能继续被fetch，故报游标不存在。

解决方案

因此决定将commit游标提交之后，可以继续使用fetch进行结果集的操作的功能利用GUC参数lightdb_cursor_after_commit 进行限制，去掉之前使用全局变量存储持有的portal的全部逻辑。
lightdb_cursor_after_commit 为off,不能在一个事务提交之后，再去fetch
操作这个结果集;为on时，一个事务提交之后，这个游标还可以继续使用。

测试

lightdb_cursor_after_commit 设置成 off

set lightdb_cursor_after_commit to off;                              
create function fg(ref inout refcursor) return int as
begin             
open ref for select * from nested_tab;
return 0;
end;
/
CREATE FUNCTION
lightdb@test_createdb_oracle=# begin;
BEGIN
lightdb@test_createdb_oracle=*# select fg('cf');fg 
----0
(1 row)lightdb@test_createdb_oracle=*# fetch all in cf;id | name  |  job  | age 
----+-------+-------+-----1 | asda  | gfdgd |  122 | sdfsd | cvxvx |  143 | uyiy  | mmbv  |  16
(3 rows) 

lightdb_cursor_after_commit 设置成 on

set lightdb_cursor_after_commit to on; 
create or replace function fg(ref inout refcursor) return int as
begin             
open ref for select * from nested_tab;
return 0;
end;
/
lightdb@test_createdb_oracle=#  begin;
BEGIN
lightdb@test_createdb_oracle=*# select fg('cf');fg 
----0
(1 row)lightdb@test_createdb_oracle=*# fetch all in cf;id | name  |  job  | age 
----+-------+-------+-----1 | asda  | gfdgd |  122 | sdfsd | cvxvx |  143 | uyiy  | mmbv  |  16
(3 rows)lightdb@test_createdb_oracle=*# commit;
COMMIT
lightdb@test_createdb_oracle=# fetch all in cf;id | name | job | age 
----+------+-----+-----
(0 rows)lightdb@test_createdb_oracle=# fetch all in cf;
ERROR:  cursor "cf" does not exist

java测试：

package test;import java.math.BigDecimal;
import java.sql.*;public class PGJdbcOOMTest {public static void main(String[] args) {Connection conn = null;Statement stmt = null;ResultSet rs = null;try {Class.forName("org.postgresql.Driver");java.lang.String  dbURL = "jdbc:postgresql://192.168.105.161:5432/test_hs_oracle";conn = DriverManager.getConnection(dbURL, "lightdb", "1");//Thread.sleep(50000);conn.setAutoCommit(false); //NOTE: 为了设置fetchSize,必须设置为false// 语句stmt = conn.createStatement();stmt.setFetchSize(1);System.out.println("ps.getQueryTimeout():" + stmt.getQueryTimeout());System.out.println("ps.getFetchSize():" + stmt.getFetchSize());System.out.println("ps.getFetchDirection():" + stmt.getFetchDirection());System.out.println("ps.getMaxFieldSize():" + stmt.getMaxFieldSize());// 查询//rs = stmt.executeQuery("set lightdb_cursor_after_commit to on");//rs = stmt.executeQuery("set lightdb_syntax_compatible_type to oracle");ResultSet resultSet = stmt.executeQuery("SELECT pg_backend_pid()");rs = stmt.executeQuery("SELECT * FROM nested_tab;");while(rs.next()){System.out.println(rs.getObject(1));connmit();}} catch (Exception e) {System.err.println(e.getMessage());e.printStackTrace();}finally {try {if(rs != null){rs.close();}} catch (SQLException e) {System.err.println(e.getMessage());e.printStackTrace();}try {if(stmt != null) {stmt.close();}} catch (SQLException e) {System.err.println(e.getMessage());e.printStackTrace();}try {if(conn != null) {conn.close();}} catch (SQLException e) {System.err.println(e.getMessage());e.printStackTrace();}}}}

–lightdb_cursor_after_commit 设置成 off

–lightdb_cursor_after_commit 设置成 on

针对for update和for share测试

set lightdb_cursor_after_commit to on

for update

create table nested_tab(id int primary key, name varchar2(100), job varchar2(100), age int);
insert into nested_tab values (1, 'asda', 'gfdgd', 12);
insert into nested_tab values (2, 'sdfsd', 'cvxvx', 14);
insert into nested_tab values (3, 'uyiy', 'mmbv', 16);create  or replace function fg(ref inout refcursor) return int as
begin             
open ref for select * from nested_tab for update;
return 0;
end;
/lightdb@test_hs_oracle=#  begin;
BEGIN
lightdb@test_hs_oracle=*# select fg('cf');fg 
----0
(1 row)lightdb@test_hs_oracle=*# fetch all in cf;id | name  |  job  | age 
----+-------+-------+-----1 | asda  | gfdgd |  122 | sdfsd | cvxvx |  143 | uyiy  | mmbv  |  16
(3 rows)lightdb@test_hs_oracle=*# commit;
COMMIT
lightdb@test_hs_oracle=# fetch all in cf;id | name | job | age 
----+------+-----+-----
(0 rows)lightdb@test_hs_oracle=# fetch all in cf;
ERROR:  cursor "cf" does not exist

for share

create  or replace function fg(ref inout refcursor) return int as
begin             
open ref for select * from nested_tab for share;
return 0;
end;
/lightdb@test_hs_oracle=# begin;
BEGIN
lightdb@test_hs_oracle=*# select fg('cf');fg 
----0
(1 row)lightdb@test_hs_oracle=*# fetch all in cf;id | name  |  job  | age 
----+-------+-------+-----1 | asda  | gfdgd |  122 | sdfsd | cvxvx |  143 | uyiy  | mmbv  |  16
(3 rows)lightdb@test_hs_oracle=*#  commit;
COMMIT
lightdb@test_hs_oracle=# fetch all in cf;id | name | job | age 
----+------+-----+-----
(0 rows)lightdb@test_hs_oracle=# fetch all in cf;
ERROR:  cursor "cf" does not exist

分布式测试

lightdb分布式参照：分布式

set lightdb_cursor_after_commit to off

create table nested_tab(id int primary key, name varchar2(100), job varchar2(100), age int);
insert into nested_tab values (1, 'asda', 'gfdgd', 12);
insert into nested_tab values (2, 'sdfsd', 'cvxvx', 14);
insert into nested_tab values (3, 'uyiy', 'mmbv', 16);select create_distributed_table('nested_tab','id');create function fg(ref inout refcursor) return int as
begin             
open ref for select * from nested_tab;
return 0;
end;
/
lightdb@test_hs_oracle=# begin;
BEGIN
lightdb@test_hs_oracle=*# select fg('cf');fg 
----0
(1 row)lightdb@test_hs_oracle=*# fetch all in cf;id | name  |  job  | age 
----+-------+-------+-----1 | asda  | gfdgd |  123 | uyiy  | mmbv  |  162 | sdfsd | cvxvx |  14
(3 rows)lightdb@test_hs_oracle=*# commit;
COMMIT
lightdb@test_hs_oracle=# fetch all in cf;
ERROR:  cursor "cf" does not exist

set lightdb_cursor_after_commit to on

create table nested_tab(id int primary key, name varchar2(100), job varchar2(100), age int);
insert into nested_tab values (1, 'asda', 'gfdgd', 12);
insert into nested_tab values (2, 'sdfsd', 'cvxvx', 14);
insert into nested_tab values (3, 'uyiy', 'mmbv', 16);select create_distributed_table('nested_tab','id');create function fg(ref inout refcursor) return int as
begin             
open ref for select * from nested_tab;
return 0;
end;
/lightdb@test_hs_oracle=# begin;
BEGIN
lightdb@test_hs_oracle=*# select fg('cf');fg 
----0
(1 row)lightdb@test_hs_oracle=*# fetch all in cf;id | name  |  job  | age 
----+-------+-------+-----1 | asda  | gfdgd |  123 | uyiy  | mmbv  |  162 | sdfsd | cvxvx |  14
(3 rows)lightdb@test_hs_oracle=*# commit;
COMMITlightdb@test_hs_oracle=# fetch all in cf;id | name | job | age 
----+------+-----+-----
(0 rows)lightdb@test_hs_oracle=# fetch all in cf;
ERROR:  cursor "cf" does not exist

for update/for share

create  or replace function fg(ref inout refcursor) return int as
begin             
open ref for select * from nested_tab for update;
return 0;
end;
/
lightdb@test_hs_oracle=# create  or replace function fg(ref inout refcursor) return int as
lightdb@test_hs_oracle$# begin             
lightdb@test_hs_oracle$# open ref for select * from nested_tab for update;
lightdb@test_hs_oracle$# return 0;
lightdb@test_hs_oracle$# end;
lightdb@test_hs_oracle$# /
CREATE FUNCTION
lightdb@test_hs_oracle=# begin;
BEGIN
lightdb@test_hs_oracle=*# select fg('cf');
ERROR:  could not run distributed query with FOR UPDATE/SHARE commands
HINT:  Consider using an equality filter on the distributed table's partition column.
CONTEXT:  SQL statement "select * from nested_tab for update"
PL/oraSQL function fg(refcursor) line 3 at OPEN

总结

set lightdb_cursor_after_commit to on；在同一个会话中的后续事务中还能够继续访问该游标（ 但是如果创建事务被中止，游标会被移除）。对于for update和for share lightdb_cursor_after_commit 参数使能单机模式还是支持的，分布式模式下由于不支持for update和for share直接报错。java端同理。
参见：declare