10일차 # 8-26: Transaction & Read Consistency

- Read Consistency (읽기 일관성)

    1) Readers do NOT wait for writers

    2) Writers do NOT wait for readers

        [Session1]                                                 [Session2]

  -- Read consistency

  create table t_book -- DDL

  (no number,

   name varchar2(10));

  desc t_book

  insert into t_book values (1000, 'Jack1'); -- DML

  insert into t_book values (2000, 'Java');

  select * from t_book;

  NO NAME

----- ----------

1000 Jack1

2000 Java

desc t_book

select * from t_book;

no rows selected

  commit;

select * from t_book;

  NO NAME

----- ----------

1000 Jack1

2000 Java

  -- Lock

  update t_book

  set name = 'Luke'

  where no = 1000;

update t_book

set name = 'Lake'

where no = 1000;

|wait!

  rollback;

1 row updated.

rollback;

  -- Deadlock

  update t_book

  set name = 'Luke'

  where no = 1000;

update t_book

set name = 'James'

where no = 2000;

  update t_book

  set name = 'James'

  where no = 2000; 

  |wait!

update t_book

set name = 'Lake'

where no = 1000;

|wait!

  ORA-00060: deadlock detected 

  while waiting for resource

  commit;

1 row updated.

commit;