| Author |
Message |
< Advanced Erlang/OTP ~ Mnesia transaction inside an mnesia transaction etc... |
| Ludvig |
 Posted: Mon Aug 07, 2006 7:45 pm |
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User
Joined: 20 Jul 2006
Posts: 38
Location: London
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If you have a Mnesia transaction inside another mnesia transaction and the inner transaction fails, will the the databse do a full rollover on the whole transaction or just the inner transaction?? Or what will happen??
Example:
Code:
func1(Key) ->
Fun = fun() ->
Result = mensia:read({test,key}),
func2(Result),
mnesia:write({test2,["hi","ho"]})
end,
mnesia:transaction(Fun).
func2(Result) ->
Fun = fun() ->
mnesia:write({test2,Result})
end,
mnesia:transaction(Fun).
-------------------
Really bad intendention.. |
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| oscarh |
| Posted: Wed Aug 23, 2006 12:55 pm |
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User
Joined: 20 Jul 2006
Posts: 22
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If the inner transaction is aborted, only that one is affected.
Code:
-module(test).
-compile(export_all).
-record(test, {id, value}).
create_table() ->
mnesia:create_table(test, []).
transaction() ->
mnesia:transaction(fun() ->
mnesia:write(#test{id = 1, value = "test 1"}),
mnesia:write(#test{id = 2, value = "test 2"}),
transaction_2(),
mnesia:write(#test{id = 3, value = "test 3"})
end
).
transaction_2() ->
mnesia:transaction(fun()->
[Record] = mnesia:read(1),
mnesia:write(Record#test{id = 1, value = "updated test 1"}),
mnesia:abort(testing_abort)
end).
Code: Eshell V5.4.9 (abort with ^G)
1> application:start(mnesia).
ok
2> test:create_table().
{atomic,ok}
3> mnesia:dirty_all_keys(test).
[]
4> test:transaction().
{atomic,ok}
5> mnesia:dirty_all_keys(test).
[1,2,3]
You could check for the result of the inner one:
Code:
-module(test).
-compile(export_all).
-record(test, {id, value}).
create_table() ->
mnesia:create_table(test, []).
transaction() ->
mnesia:transaction(fun() ->
mnesia:write(#test{id = 1, value = "test 1"}),
mnesia:write(#test{id = 2, value = "test 2"}),
case transaction_2() of
{atomic, _Result} -> ok;
{aborted, _Reason} -> mnesia:abort(inner_aborted)
mnesia:write(#test{id = 3, value = "test 3"})
end
).
transaction_2() ->
mnesia:transaction(fun()->
[Record] = mnesia:read(1),
mnesia:write(Record#test{id = 1, value = "updated test 1"}),
mnesia:abort(testing_abort)
end).
Code: Eshell V5.4.9 (abort with ^G)
1> application:start(mnesia).
ok
2> test:create_table().
{atomic,ok}
3> mnesia:dirty_all_keys(test).
[]
4> test:transaction().
{aborted,inner_aborted}
5> mnesia:dirty_all_keys(test).
[]
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| Ludvig |
| Posted: Wed Aug 23, 2006 1:05 pm |
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User
Joined: 20 Jul 2006
Posts: 38
Location: London
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Thanks for trying to solve my problem. But your explanation gave me a new problem. In your code:
Code: -module(test).
-compile(export_all).
-record(test, {id, value}).
create_table() ->
mnesia:create_table(test, []).
transaction() ->
mnesia:transaction(fun() ->
mnesia:write(#test{id = 1, value = "test 1"}),
mnesia:write(#test{id = 2, value = "test 2"}),
case transaction_2() of
{atomic, _Result} -> ok;
{aborted, _Reason} -> mnesia:abort(inner_aborted)
end,
mnesia:write(#test{id = 3, value = "test 3"})
end
).
transaction_2() ->
mnesia:transaction(fun()->
[Record] = mnesia:read(1),
mnesia:write(Record#test{id = 1, value = "updated test 1"}),
mnesia:abort(testing_abort)
end).
I change it to this:
Code: -module(test).
-compile(export_all).
-record(test, {id, value}).
create_table() ->
mnesia:create_table(test, []).
transaction() ->
mnesia:transaction(fun() ->
mnesia:write(#test{id = 1, value = "test 1"}),
mnesia:write(#test{id = 2, value = "test 2"}),
case transaction_2() of
{atomic, _Result} -> ok;
{aborted, _Reason} -> mnesia:abort(inner_aborted)
end,
mnesia:write(#test{id = 3, value = "test 3"}),
mnesia:abort(problem_in_paradise)
end
).
transaction_2() ->
mnesia:transaction(fun()->
[Record] = mnesia:read(1),
mnesia:write(Record#test{id = 1, value = "updated test 1"}),
end).
As you can see I changed so that transaction_2 dosen't abort. But instead an aborted is done after transaction_2 is finished.
How will this affect the transactions and is there any way to abort the transaction_2 after it has been finished? |
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| oscarh |
| Posted: Wed Aug 23, 2006 1:33 pm |
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User
Joined: 20 Jul 2006
Posts: 22
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First of all, in the future I should try and post code that compiles.
However, the inner transaction is never really comitted before the outer one is:
Code:
-module(test).
-compile(export_all).
-record(test, {id, value}).
create_table() ->
mnesia:create_table(test, []).
transaction() ->
mnesia:transaction(fun() ->
mnesia:write(#test{id = 1, value = "test 1"}),
mnesia:write(#test{id = 2, value = "test 2"}),
case transaction_2() of
{atomic, _Result} -> ok;
{aborted, Reason} -> mnesia:abort({inner_aborted, Reason})
end,
mnesia:write(#test{id = 3, value = "test 3"}),
mnesia:abort(problem_in_paradise)
end
).
transaction_2() ->
mnesia:transaction(fun()->
[Record] = mnesia:read({test, 1}),
mnesia:write(Record#test{value = "updated test 1"}),
mnesia:write(#test{id = 4, value = "test 4"})
end).
Gives:
Code:
1> application:start(mnesia).
ok
2> test:create_table().
{atomic,ok}
3> mnesia:dirty_all_keys(test).
[]
4> test:transaction().
{aborted,problem_in_paradise}
5> mnesia:dirty_all_keys(test).
[]
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| oscarh |
| Posted: Wed Aug 23, 2006 1:47 pm |
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Joined: 20 Jul 2006
Posts: 22
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| Ludvig |
| Posted: Fri Aug 25, 2006 8:57 am |
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User
Joined: 20 Jul 2006
Posts: 38
Location: London
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Thank you!
There where some really god examples. Just what I needed. |
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