作者：阡蓝fliona | 来源：互联网 | 2023-05-18 07:18
这篇文章主要讲解了“PostgreSQL禁止的异象是什么”，文中的讲解内容简单清晰，易于学习与理解，下面请大家跟着小编的思路慢慢深入，一起来研究和学习“PostgreSQL禁止的异象是什么”吧！
测试数据
数据表idx，在id列上有索引，数据库默认的隔离级别为可串行化
15:44:16 [local:/data/run/pg12]:5120 pg12@testdb=# \d+ idx
Table "public.idx"
Column | Type | Collation | Nullable | Default | Storage | Stats
target | Description
--------+-------------------+-----------+----------+---------+----------+-------
-------+-------------
id | integer | | | | plain |
|
c1 | character varying | | | | extended |
|
Indexes:
"idx_id" btree (id)
Access method: heap
[pg12@localhost pg122db]$ grep &＃39;isolation&＃39; postgresql.conf
default_transaction_isolation = &＃39;SERIALIZABLE&＃39;
Write触发
操作序列如下：
| 时间点 | T1 | T2 | T3 |
|---|
| t1 | begin; |
|
|
| t2 | select * from idx where id = 1; |
|
|
| t3 |
| begin; |
|
| t4 |
| select * from idx where id = 10000; |
|
| t5 |
|
| begin; |
| t6 |
|
| update idx set c1 = ‘x’ where id = 10000; |
| t7 |
|
| commit; |
| t8 |
| update idx set c1 = ‘x’ where id = 1; |
|
session 2（T2）在执行update操作时会报错
-- session 2
15:46:52 [local:/data/run/pg12]:5120 pg12@testdb=#* update idx set c1 = &＃39;x&＃39; where id = 1;
ERROR: could not serialize access due to read/write dependencies among transactions
DETAIL: Reason code: Canceled on identification as a pivot, during write.
HINT: The transaction might succeed if retried.
15:47:10 [local:/data/run/pg12]:5120 pg12@testdb=#!
Read触发
操作序列如下：
| 时间点 | T1 | T2 | T3 |
|---|
| t1 | begin; |
|
|
| t2 | select * from idx where id = 1; |
|
|
| t3 |
| begin; |
|
| t4 |
| update idx set c1 = ‘x1’ where id = 1; |
|
| t5 |
|
| begin; |
| t6 |
|
| update idx set c1 = ‘x’ where id = 10000; |
| t7 |
|
| commit; |
| t8 |
| select * from idx where id = 10000; |
|
session 2（T2）在执行select操作时会报错
15:54:41 [local:/data/run/pg12]:5120 pg12@testdb=#* select * from idx where id = 10000;
ERROR: could not serialize access due to read/write dependencies among transactions
DETAIL: Reason code: Canceled on conflict out to pivot 423284, during read.
HINT: The transaction might succeed if retried.
15:55:16 [local:/data/run/pg12]:5120 pg12@testdb=#!
commit触发
操作序列如下：
| 时间点 | T1 | T2 |
|---|
| t1 | begin; |
|
| t2 | select * from idx where id = 1; |
|
| t3 | update tbl set c1 = ‘x’ where id = 10000; |
|
| t4 |
| begin; |
| t5 |
| select * from idx where id = 10000; |
| t6 |
| update idx set c1 = ‘x’ where id = 1; |
| t7 |
| commit; |
| t8 | commit; |
|
T1执行commit的时候会报错：
16:07:50 [local:/data/run/pg12]:5120 pg12@testdb=#* commit;
ERROR: could not serialize access due to read/write dependencies among transactions
DETAIL: Reason code: Canceled on identification as a pivot, during commit attempt.
HINT: The transaction might succeed if retried.
感谢各位的阅读，以上就是“PostgreSQL禁止的异象是什么”的内容了，经过本文的学习后，相信大家对PostgreSQL禁止的异象是什么这一问题有了更深刻的体会，具体使用情况还需要大家实践验证。这里是编程笔记，小编将为大家推送更多相关知识点的文章，欢迎关注！
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