postgresql 事務隔離級別 set transaction isolation level

os: centos 7.4
db: postgresql 10.11

postgresql 默認的 isolation level 爲 read committed，可以調整隔離級別。

版本

# cat /etc/centos-release
CentOS Linux release 7.4.1708 (Core) 
# 
# 
# su - postgres
Last login: Wed Jan 15 18:34:12 CST 2020 on pts/0
$
$
$ psql -c "select version();"
                                                 version                                                  
----------------------------------------------------------------------------------------------------------
 PostgreSQL 10.11 on x86_64-pc-linux-gnu, compiled by gcc (GCC) 4.8.5 20150623 (Red Hat 4.8.5-39), 64-bit
(1 row)

set transaction isolation level

postgres=# select name,setting from pg_settings where name like 'transaction%';
          name          |    setting     
------------------------+----------------
 transaction_deferrable | off
 transaction_isolation  | read committed
 transaction_read_only  | off
(3 rows)

postgres=# \h set transaction
Command:     SET TRANSACTION
Description: set the characteristics of the current transaction
Syntax:
SET TRANSACTION transaction_mode [, ...]
SET TRANSACTION SNAPSHOT snapshot_id
SET SESSION CHARACTERISTICS AS TRANSACTION transaction_mode [, ...]

where transaction_mode is one of:

    ISOLATION LEVEL { SERIALIZABLE | REPEATABLE READ | READ COMMITTED | READ UNCOMMITTED }
    READ WRITE | READ ONLY
    [ NOT ] DEFERRABLE

postgres=# set transaction isolation level serializable;
WARNING:  SET TRANSACTION can only be used in transaction blocks
SET

serializable

postgres=# begin;
postgres=# set transaction isolation level serializable;
postgres=# show transaction_isolation;
 transaction_isolation 
-----------------------
 serializable
(1 row)

postgres=# rollback;

repeatable read

postgres=# begin;
postgres=# set transaction isolation level repeatable read;
postgres=# show transaction_isolation;
 transaction_isolation 
-----------------------
 repeatable read
(1 row)

postgres=# rollback;

read committed

postgres=# begin;
postgres=# set transaction isolation level read committed;
postgres=# show transaction_isolation;
 transaction_isolation 
-----------------------
 read committed
(1 row)

postgres=# rollback;

read uncommitted

postgres=# begin;
postgres=# set transaction isolation level read uncommitted;
postgres=# show transaction_isolation;
 transaction_isolation 
-----------------------
 read uncommitted
(1 row)

postgres=# rollback;

begin

postgres=# \h begin
Command:     BEGIN
Description: start a transaction block
Syntax:
BEGIN [ WORK | TRANSACTION ] [ transaction_mode [, ...] ]

where transaction_mode is one of:

    ISOLATION LEVEL { SERIALIZABLE | REPEATABLE READ | READ COMMITTED | READ UNCOMMITTED }
    READ WRITE | READ ONLY
    [ NOT ] DEFERRABLE

serializable

postgres=# begin transaction isolation level serializable;
postgres=# show transaction_isolation;
 transaction_isolation 
-----------------------
 serializable
(1 row)

postgres=# rollback;

repeatable read

postgres=# begin transaction isolation level repeatable read;
postgres=# show transaction_isolation;
 transaction_isolation 
-----------------------
 repeatable read
(1 row)

postgres=# rollback;

read committed

postgres=# begin transaction isolation level read committed;
postgres=# show transaction_isolation;
 transaction_isolation 
-----------------------
 read committed
(1 row)

postgres=# rollback;

read uncommitted

postgres=# begin transaction isolation level read uncommitted;
postgres=# show transaction_isolation;
 transaction_isolation 
-----------------------
 read uncommitted
(1 row)

postgres=# rollback;

參考:
http://postgres.cn/docs/10/sql-set-transaction.html