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用考虑分布式。后续测试分布式时，发现持有portal后，会对querydesc进行非空判断，若querydesc为空，会造成崩溃。加上querydesc判断之后，导致之前使用一个全局变量接收portal的方案失败，一个sql执行完，portal就被释放了。在事务中调用打开游标的函数，打开的游标不能继续被fetch，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，一个事务提交时候，这个游标还继续存在。

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 |  12
  2 | sdfsd | cvxvx |  14
  3 | 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 |  12
  2 | sdfsd | cvxvx |  14
  3 | 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));
                conn.commit();
            }
        } 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
test1
–lightdb_cursor_after_commit 设置成 on

test2

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 |  12
  2 | sdfsd | cvxvx |  14
  3 | 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

test5

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 |  12
  2 | sdfsd | cvxvx |  14
  3 | 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

test7

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 |  12
  3 | uyiy  | mmbv  |  16
  2 | 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

test3

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 |  12
  3 | uyiy  | mmbv  |  16
  2 | sdfsd | cvxvx |  14
(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

tesst4

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

test5

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