mnesia_frag ????

Rikard Johansson <>
Mon Jan 16 14:01:41 CET 2006



As Ulf says, you should use mnesia:read within the ReadFun,

ReadFun = fun(Db,DBKey) ->  mnesia:read({Db, DBKey}) end.

However, if you want "dirty access" you can use the 'sync_dirty' 
AccessContext.

mnesia:activity(sync_dirty, ReadFun, [profile_db,777], mnesia_frag).

/Rikard

Ulf Wiger (AL/EAB) wrote:
>  
> Don't use mnesia:dirty_read/2 as your read function.
> Try with mnesia:read({Tab, Key}) instead.
>  
> Dirty_read() goes directly to the (base-) table, and has no concept of 
> mnesia_frag.
>  
> /Uffe
> 
>     ------------------------------------------------------------------------
>     *From:* 
>     [mailto:] *On Behalf Of *Sanjaya
>     Vitharana
>     *Sent:* den 16 januari 2006 13:32
>     *To:* 
>     *Subject:* mnesia_frag ????
> 
>     Hi .. !!!
>      
>     Can any one show me where I'm doing wrong, I'm trying to write a
>     single record & retrive it using mnesia_frag.
>      
>     But it's not working :( for me.
>      
>     ()29 <mailto:)29>>
>     mnesia:table_info(profile_db, frag_properties).
>     [{base_table,profile_db},                   
>      {foreign_key,undefined},
>      {hash_module,mnesia_frag_hash},
>      {hash_state,{hash_state,30,15,4}},
>      {n_fragments,30},
>      {node_pool,[]}]
>     ()31 <mailto:)31>> WriteFun1 = fun(DbFile,
>     Rec) -> mnesia:write(DbFile, Rec, write)end.
>     #Fun<erl_eval.12.2225172>
>     ()32 <mailto:)32>>
>     mnesia:activity(transaction, WriteFun1, [profile_db,
>     {profile_db,777,"test",333,1234,5678,1234}], mnesia_frag).
>     ok  --- Here it shows as it works
>     ()33 <mailto:)33>> ReadFun = fun(Db,DBKey)
>     ->  mnesia:dirty_read(Db, DBKey)end.
>     #Fun<erl_eval.12.2225172>
>     ()34 <mailto:)34>>
>     mnesia:activity(transaction, ReadFun, [profile_db,777], mnesia_frag).
>     [] -- but empty list given when try to retrive
>     ()35 <mailto:)35>>
>     mnesia:dirty_first(profile_db).
>     '$end_of_table'  --- since the db should contains only 2 records, I
>     tried this. but :(
>     ()36 <mailto:)36>>
>      
>      
>     Furthermore I have used below, to create the DB.
>      
>     -record(profile_db, {mobile_no, prof_details, type,
>     last_update_date, first_creation_date, fax_no}).
>      
>        Res = mnesia:create_table(profile_db,[
>                           {disc_copies, NodeList},
>                           {type, ordered_set},
>                           {index, [type, last_update_date,
>     first_creation_date, fax_no]},
>                           {frag_properties, [{n_fragments, 30}]},
>                           {attributes, record_info(fields, profile_db)}
>                           ]),
>      
>     ----------------------------------------------------------------------------------------------------------------------------------------------------
>     consider the mnesia:info() result below, and note that the
>     profile_db_frag2: with 1        records occupying 95       words of mem
>     disc_copies        = [schema]
>     but I have used  {disc_copies, NodeList}
>     ----------------------------------------------------------------------------------------------------------------------------------------------------
>      
>     ()43 <mailto:)43>>
>     mnesia:info().                                
>     ---> Processes holding locks <---
>     ---> Processes waiting for locks <---
>     ---> Participant transactions <---
>     ---> Coordinator transactions <---
>     ---> Uncertain transactions <---
>     ---> Active tables <---
>     profile_db     : with 0        records occupying 70       words of mem
>     profile_db_frag2: with 1        records occupying 95       words of mem
>     ......
>     profile_db_frag13: with 1        records occupying 95       words of mem
>     .......
>     profile_db_frag29: with 0        records occupying 70       words of mem
>     profile_db_frag30: with 0        records occupying 70       words of mem
>     schema         : with 31       records occupying 4380     words of mem
>     ===> System info in version "4.2.3", debug level = none <===
>     opt_disc. Directory "/usr2/omni_vm_prof/db/vmdb" is used.
>     use fallback at restart = false
>     running db nodes   = []
>     stopped db nodes   = []
>     master node tables = []
>     remote             = []
>     ram_copies         = [profile_db,
>                           profile_db_frag10,
>                           profile_db_frag11,
>                          
>                           ...
>                          
>                           profile_db_frag8,
>                           profile_db_frag9]
>     disc_copies        = [schema]
>     disc_only_copies   = []
>     [{,disc_copies}] = [schema]
>     [{,ram_copies}] = [profile_db_frag30,
>                                     profile_db_frag29,
>                                    
>                                     .....
>      
>                                     profile_db_frag3,
>                                     profile_db_frag2,
>                                     profile_db]
>     12 transactions committed, 5 aborted, 0 restarted, 0 logged to disc
>     0 held locks, 0 in queue; 0 local transactions, 0 remote
>     0 transactions waits for other nodes: []
>     ok
>     ()44 <mailto:)44>>             
>      
>      
>     I have confused with the results, can anyone explane this ??
>      
>     Thanks in advance.
>      
>     Sanjaya Vitharana



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