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
–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 | 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
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
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
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
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