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mnesia:delect_object只删除索引问题

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前言

最近遇到一个奇怪的问题，mnesia数据有时能查出来有时查不出来，细查发现是mnesia:delect_object删除时，只删除了索引，没有删除具体的数据

问题重现

  1. 表结构:
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-record(gordon_test, {
    idr,    % {id, pid}
    id,
    pid,
    locale,
    time = os:timestamp()
}).
  1. 初使化代码:
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mnesia:create_table(gordon_test, [
    {ram_copies, [node() | nodes()]},
    {attributes, record_info(fields, gordon_test)}
]),
mnesia:add_table_index(gordon_test, id),
mnesia:add_table_index(gordon_test, pid).
  1. 插入数据:
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mnesia:dirty_write(gordon_test, {gordon_test, {1, 1}, 1, 1, "", "", os:timestamp()}).
mnesia:dirty_write(gordon_test, {gordon_test, {2, 2}, 2, 2, "", "", os:timestamp()}).
mnesia:dirty_write(gordon_test, {gordon_test, {3, 3}, 3, 3, "", "", os:timestamp()}).

3.查询:

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Id = 3,
Pid = 3,
% 查出id=3的所有记录，都能查出一条记录
mnesia:dirty_index_read(gordon_test, Id, #gordon_test.id),
mnesia:dirty_index_match_object(#gordon_test{idr = '$1',id=Id, _='_'}, #gordon_test.id),
  1. 执行删除:
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mnesia:dirty_delete_object(X#gordon_test{locale = aaaa}).
or
Trans = fun() ->
    mnesia:delete_object(X#gordon_test{locale = aaaa})
        end,
mnesia:transaction(Trans)
  1. 两次查询，dirty_index_read查不到数据:
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% 数据查询为空
mnesia:dirty_index_read(gordon_test, Id, #gordon_test.id),
% 数据不变
mnesia:dirty_index_match_object(#gordon_test{idr = '$1',id=Id, _='_'}, #gordon_test.id),

问题定位

查文档:

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If a table is of type bag, it can sometimes be needed to delete only some of the records with a certain key. 
This can be done with the function delete_object/3. A complete record must be supplied to this function.

The semantics of this function is context-sensitive. For details, see mnesia:activity/4. 
In transaction-context, it acquires a lock of type LockKind on the record. 
Currently, the lock types write and sticky_write are supported.

深层研究

待继续 @todo