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| mattevans |
 Posted: Tue Jun 22, 2010 11:20 pm |
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User
Joined: 07 Jun 2009
Posts: 47
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Hi,
I have a fragmented mnesia table that I need to add a second index to.
It appears that to get this working I need to call mnesia:add_table_index/2 for each fragment.
i.e.
mnesia:add_table_index(content_table,file_id).
mnesia:add_table_index(content_table_frag2,file_id).
mnesia:add_table_index(content_table_frag3,file_id).
....
mnesia:add_table_index(content_table_fragN,file_id).
Likewise, to do an index read of the fragmented table I need to search each fragment in turn:
mnesia:activity(sync_dirty,fun mnesia:dirty_index_read/3,[content_table,{1,1,1},file_id],mnesia_frag).
mnesia:activity(sync_dirty,fun mnesia:dirty_index_read/3,[content_table_frag2,{1,1,1},file_id],mnesia_frag).
....
until match found, or
....
mnesia:activity(sync_dirty,fun mnesia:dirty_index_read/3,[content_table_fragN,{1,1,1},file_id],mnesia_frag).
I guess searching through multiple fragments is quicker than a brute-force mnesia:match_object/1 or mnesia:select/4, but I was wondering if there is a better way to do this?
I could, of course, have my own secondary index table (in the example above the key would be file_id and the data would be the primary key I ultimately want). But I now need to ensure the two tables remain in sync.
Is there another way anyone is aware of?
Thanks
Matt
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| chandru.m |
| Posted: Wed Jun 23, 2010 8:47 am |
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Joined: 24 Oct 2007
Posts: 85
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Hi Matt,
On 23 June 2010 00:18, Evans, Matthew <mevans@verivue.com> wrote:
> Hi,
>
> I have a fragmented mnesia table that I need to add a second index to.
>
> It appears that to get this working I need to call mnesia:add_table_index/2
> for each fragment.
>
>
Yes - that is correct.
> Likewise, to do an index read of the fragmented table I need to search each
> fragment in turn:
>
Not really - the following code should do.
dirty_index_read(Tab, SecondaryKey, Pos) ->
F = fun(T, Sk, P) -> mnesia:index_read(T,Sk,P) end,
mnesia:activity(async_dirty, F, [Tab, SecondaryKey, Pos], mnesia_frag).
cheers
Chandru
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| mattevans |
| Posted: Wed Jun 23, 2010 12:08 pm |
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Joined: 07 Jun 2009
Posts: 47
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Many thanks. I was thrown by me doing:
74> mnesia:activity(sync_dirty,fun mnesia:dirty_index_read/3,[cmfs_content_uuid_table,{1,1,1},file_id],mnesia_frag).
[]
When I should've done:
73> mnesia:activity(sync_dirty,fun mnesia:index_read/3,[cmfs_content_uuid_table,{1,1,1},file_id],mnesia_frag).
[#cmfs_content_uuid_table{content_uuid = 1,
file_id = {1,1,1},
nts_start_offset = '_',nts_duration = '_',start_time = '_',
end_time = '_',restripe_time = '_',version_id = '_',
start_of_content = '_',average_bit_rate = '_',
peak_bit_rate = '_',program_id = '_',frame_rate_code = '_',
video_format = '_',video_size = '_',pid_info_list = '_',
duration = '_',media_type = '_',size = '_',data_state = '_',
checksum = '_'}]
________________________________________
From: Chandru [chandrashekhar.mullaparthi@gmail.com]
Sent: Wednesday, June 23, 2010 4:44 AM
To: Evans, Matthew
Cc: erlang-questions@erlang.org
Subject: Re: [erlang-questions] mnesia secondary index
Hi Matt,
On 23 June 2010 00:18, Evans, Matthew <mevans@verivue.com<mailto:mevans@verivue.com>> wrote:
Hi,
I have a fragmented mnesia table that I need to add a second index to.
It appears that to get this working I need to call mnesia:add_table_index/2 for each fragment.
Yes - that is correct.
Likewise, to do an index read of the fragmented table I need to search each fragment in turn:
Not really - the following code should do.
dirty_index_read(Tab, SecondaryKey, Pos) ->
F = fun(T, Sk, P) -> mnesia:index_read(T,Sk,P) end,
mnesia:activity(async_dirty, F, [Tab, SecondaryKey, Pos], mnesia_frag).
cheers
Chandru
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| wuji |
| Posted: Wed Sep 12, 2012 8:43 am |
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Joined: 10 Aug 2012
Posts: 654
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