New mnesia events

[Chandrashekhar Mullaparthi]

It's pretty neat - but what if the record definition for schema itself
changes.... I need the definition for the schema record to know the name of
the table created - Isn't that internal to mnesia??

cheers,
Chandru

> -----Original Message-----
> From: Hakan Mattsson [mailto:hakan@REDACTED]
> Sent: 9 March 2001 11:02
> To: Chandrashekhar Mullaparthi
> Cc: 'Erlang mailing list'
> Subject: Re: New mnesia events
> 
> 
> On Fri, 9 Mar 2001, Chandrashekhar Mullaparthi wrote:
> 
> Chandrashekhar> I think it will be useful if mnesia could 
> issue the following events.
> Chandrashekhar>  
> Chandrashekhar> {table_created, Table}
> Chandrashekhar> {table_deleted, Table}
> 
> Don't you like mnesia:subscribe({table, schema})?
> 
> Chandrashekhar> {table_available, Table} - This would be like 
> an asynchronous version of
> Chandrashekhar> mnesia:wait_for_tables(Tables, Timeout). 
> Right now, I have some very big
> Chandrashekhar> tables and a process which uses them doesn't 
> know when they will be
> Chandrashekhar> available. But it can't wait forever in 
> mnesia:wait_for_tables - the way to
> Chandrashekhar> do it now would be to have a timer to 
> periodically check if the required
> Chandrashekhar> table is available. Would be easier if my 
> process could just subscribe for
> Chandrashekhar> an event.
> Chandrashekhar>  
> Chandrashekhar> The first two would be useful in a case where 
> tables are created/deleted
> Chandrashekhar> dynamically in an application. The way to do 
> it now would be to use
> Chandrashekhar> mnesia:report_event - but it would be nice to 
> have a standard way of knowing
> Chandrashekhar> when a table has been created/deleted.
> 
> You always have the option of spawning a separate process in order
> to perform the monitoring of when tables gets loaded, but my original 
> idea was to handle thos via the event mechanism.
> 
> Chandrashekhar> The table event {delete, {Tab, Key}, 
> ActivityId} is not issued for each key
> Chandrashekhar> when a table is deleted - which is sensible - 
> but {table_deleted, Table}
> Chandrashekhar> would nicely fill the gap.
> 
> As mentioned above, use the mnesia:subscribe/1 function.
> 
> /Håkan
> 
> ---
> Håkan Mattsson
> Ericsson
> Computer Science Laboratory
> http://www.ericsson.se/cslab/~hakan
> 
> 
> --- CUT --- CUT --- CUT --- CUT --- CUT --- CUT --- CUT --- CUT --
> unix> erl
> Erlang (BEAM) emulator version 5.0.2 [threads]
> 
> Eshell V5.0.2  (abort with ^G)
> 1> mnesia:start().
> ok
> 2> mnesia:subscribe({table, schema}).
> {ok,nonode@REDACTED}
> 3> mnesia:create_table(a_brand_new_table, []).
> {atomic,ok}
> 4> flush().
> Shell got {mnesia_table_event,{write,{schema,
>                                          a_brand_new_table,
>                                          [{name,a_brand_new_table},
>                                           {type,set},
>                                           
> {ram_copies,[nonode@REDACTED]},
>                                           {disc_copies,[]},
>                                           {disc_only_copies,[]},
>                                           {load_order,0},
>                                           {access_mode,read_write},
>                                           {index,[]},
>                                           {snmp,[]},
>                                           {local_content,false},
>                                           
> {record_name,a_brand_new_table},
>                                           {attributes,[key,val]},
>                                           {user_properties,[]},
>                                           {frag_properties,[]},
>                                           {cookie,
>                                               {{984,134919,30740},
>                                                nonode@REDACTED}},
>                                           {version,{{2,0},[]}}]},
>                                      {tid,3,<0.63.0>}}}
> Shell got {mnesia_table_event,{write,{schema,
>                                          a_brand_new_table,
>                                          [{name,a_brand_new_table},
>                                           {type,set},
>                                           
> {ram_copies,[nonode@REDACTED]},
>                                           {disc_copies,[]},
>                                           {disc_only_copies,[]},
>                                           {load_order,0},
>                                           {access_mode,read_write},
>                                           {index,[]},
>                                           {snmp,[]},
>                                           {local_content,false},
>                                           
> {record_name,a_brand_new_table},
>                                           {attributes,[key,val]},
>                                           {user_properties,[]},
>                                           {frag_properties,[]},
>                                           {cookie,
>                                               {{984,134919,30740},
>                                                nonode@REDACTED}},
>                                           {version,{{2,0},[]}}]},
>                                      {tid,3,<0.63.0>}}}
> 5> mnesia:delete_table(a_brand_new_table).
> {atomic,ok}
> 6> flush(). 
> Shell got {mnesia_table_event,{delete,{schema,
>                                           a_brand_new_table,
>                                           [{name,a_brand_new_table},
>                                            {type,set},
>                                            
> {ram_copies,[nonode@REDACTED]},
>                                            {disc_copies,[]},
>                                            {disc_only_copies,[]},
>                                            {load_order,0},
>                                            {access_mode,read_write},
>                                            {index,[]},
>                                            {snmp,[]},
>                                            {local_content,false},
>                                            
> {record_name,a_brand_new_table},
>                                            {attributes,[key,val]},
>                                            {user_properties,[]},
>                                            {frag_properties,[]},
>                                            {cookie,
>                                                {{984,135646,22951},
>                                                 nonode@REDACTED}},
>                                            {version,{{2,0},[]}}]},
>                                       {tid,4,<0.66.0>}}}
> ok
> BREAK: (a)bort (c)ontinue (p)roc info (i)nfo (l)oaded
>        (v)ersion (k)ill (D)b-tables (d)istribution7> 
> unix>
> 



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