问题
As the title says: will moving (without renaming) a table/partition while it's being accessed have negative consequences on any queries accessing it?
For example, say there's a long-running SELECT COUNT(*) FROM some_table.
If I were to ALTER TABLE some_table MOVE TABLESPACE some_other_tablespace, would the SELECT fail?
Would it complete, but have incorrect results? Maybe something else entirely?
The only info I could find was that moving the table to a different tablespace would require rebuilding the indices under certain circumstances, but none made mention of what happens to any active queries.
回答1:
It might fail with ORA-08103: object no longer exists.
In Oracle, readers and writers do not block each other. Which means DML and queries will not interfere with each other, excluding a few weird cases like running out of UNDO space. But moving a tablespace, or any type of ALTER or other DDL statement, is not a normal write. The multiversion concurrency control model breaks down when you run DDL, at least for the involved objects, and weird things start to happen.
Testing a large move is difficult, but you can reproduce these errors by looping through a lot of small alters and queries. In case you think this is only a theoretical issue, I have seen these errors occur in real-life, on a production database.
Warning: infinite loops below since I can't predict how long it will take to reproduce this error. But it usually only takes me tens of seconds.
--Create sample table.
drop table test1 purge;
create table test1(a number, b number)
partition by list(a) (partition p1 values(1), partition p2 values(2))
nologging tablespace users;
--Session 1
begin
loop
execute immediate '
insert /*+ append */ into test1 select mod(level,2)+1, level
from dual connect by level <= 100000';
commit;
execute immediate 'alter table test1 move partition p1 tablespace users';
end loop;
end;
/
--Session 2: Read from moved partition
declare
v_count number;
begin
loop
select count(*) into v_count from test1 where a = 1;
end loop;
end;
/
--Session 3: Read from unmoved partition
declare
v_count number;
begin
loop
select count(*) into v_count from test1 where a = 2;
end loop;
end;
/
Session 2 will eventually die with:
ORA-08103: object no longer exists
ORA-06512: at line 6
Session 3 will not fail, it is not querying an altered partition. Each partition has its own segment, and is a separate object that can potentially "no longer exist".
回答2:
A partition move WILL cause DML to fail if it is accessing the parition.
I just proved it :-/.
I was doing a large delete and tried to move a partition (alter table move partition).
The error I received was:
ORA-12801: error signaled in parallel query server P004ORA-08103: object no longer exists
来源：https://stackoverflow.com/questions/15531881/will-moving-a-table-partition-to-a-different-tablespace-interrupt-queries-access