[erlang-questions] inconsistent results with fragmented table

Chandru <>
Fri Jul 5 20:58:43 CEST 2013


How were these records written to the table in the first place? I've seen
this happen when you write to the table without using mnesia_frag as the
activity callback module.

cheers
Chandru

On 5 July 2013 16:07, Noah Schwartz <> wrote:

> I have a table of type set that worked fine as a non-fragmented table. We
> started seeing performance issues with the table and with the anticipation
> of more clients in the system, we were worried the size would exceed the 2
> GB max.
>
> The table contains chat messages and we purge records older than 7 days.
> There seem to be a number of keys that don't show up in a read activity
> but, do show up when doing a table dump, a select, or using qlc to find
> records. As such, when this purge policy runs records are found that when I
> try to delete don't actually get deleted. It almost seems like read/delete
> are working off of one set while qlc is working off of another set.
>
> Code/outputs below. As you can see for a given key read returns nothing,
> qlc returns an object, delete says it worked ok. Running the code again
> gives the same results. Am I using the fragmentation API incorrectly
> somehow?
>
> Thanks in advance
>
> *Code:*
> -module(sel).
> -include_lib("stdlib/include/qlc.hrl").
> -record(archive_message313, {owner_with_day_utc, owner, with,
> day_gregorian_seconds, messages = []}).
> -export([run/0]).
>
> run () ->
>   Owner = {"9afa8671-7e88-436c-9ad4-4cb13ad45e1e", "dj.barker.xxx.com"},
>   With = {"d735280e-d263-4e2b-beff-ed8ccaca5535", "dj.barker.xxx.com"},
>   DayUtc = {2013, 6, 28},
>   K = {Owner, With, DayUtc},
>
>   DelFun = fun () -> mnesia:delete({archive_message313, K}) end,
>   ReadFun = fun () -> mnesia:read({archive_message313, K}) end,
>
>   QlcFun = fun () ->
>     Q = qlc:q([M || M <- mnesia:table(archive_message313),
> M#archive_message313.owner_with_day_utc == K]),
>     qlc:eval(Q)
>   end,
>
>   Read = mnesia:activity(transaction, ReadFun, [], mnesia_frag),
>   Qlc = mnesia:activity(transaction, QlcFun, [], mnesia_frag),
>   Del = mnesia:activity(transaction, DelFun, [], mnesia_frag),
>
>   {read_result, Read, qlc_result, Qlc, del_result, Del}.
>
> *Output:*
> {read_result,[],qlc_result,
>              [{archive_message313,{{"9afa8671-7e88-436c-9ad4-4cb13ad45e1e",
>                                     "dj.barker.xxx.com"},
>                                    {"d735280e-d263-4e2b-beff-ed8ccaca5535",
>                                     "dj.barker.xxx.com"},
>                                    {2013,6,28}},
>                                   {"9afa8671-7e88-436c-9ad4-4cb13ad45e1e",
>                                    "dj.barker.xxx.com"},
>                                   {"d735280e-d263-4e2b-beff-ed8ccaca5535",
>                                    "dj.barker.xxx.com"},
>                                   63539596800,
>                                   [{{{2013,6,28},{13,36,34}},
>                                     {xmlelement,"forwarded",
>
> [{"xmlns","urn:xmpp:forward:0"}],
>                                                 [{xmlelement,"delay",
>
>  [{"xmlns","urn:xmpp:delay"},
>
> {"stamp","2013-06-28T13:36:34.000000Z"}],
>                                                              []},
>                                                  {xmlelement,"message",
>                                                              [{"to",
>                                                                "
> "},
>                                                                {"from",
>                                                                "
> "},
>
> {"type","chat"}],
>
>  [{xmlelement,"body",[],[...]}]}]},
>                                     1372426594.889164},
>                                    {{{2013,6,28},{13,36,35}},
>                                     {xmlelement,"forwarded",
>
> [{"xmlns","urn:xmpp:forward:0"}],
>                                                 [{xmlelement,"delay",
>
>  [{"xmlns","urn:xmpp:delay"},
>
> {"stamp","2013-06-28T13:36:35.000000Z"}],
>                                                              []},
>                                                  {xmlelement,"message",
>                                                              [{"to",
>                                                                "
> "},
>                                                               {"from",
>                                                                "
> "},
>
> {"type",[...]}],
>
>  [{xmlelement,"body",[],...}]}]},
>                                     1372426595.124266},
>                                    {{{2013,6,28},{13,36,35}},
>                                     {xmlelement,"forwarded",
>
> [{"xmlns","urn:xmpp:forward:0"}],
>                                                 [{xmlelement,"delay",
>
>  [{"xmlns","urn:xmpp:delay"},
>
> {"stamp","2013-06-28T13:36:35.000000Z"}],
>                                                              []},
>                                                  {xmlelement,"message",
>                                                              [{"to",
>                                                                "
> "},
>
> {"from",[...]},
>                                                               {[...],...}],
>
>  [{xmlelement,[...],...}]}]},
>                                     1372426595.337535}]}],
>              del_result,ok}
> --
> Noah
>
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