mnesia_log.erl

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%% ``The contents of this file are subject to the Erlang Public License,
%% Version 1.1, (the "License"); you may not use this file except in
%% compliance with the License. You should have received a copy of the
%% Erlang Public License along with this software. If not, it can be
%% retrieved via the world wide web at http://www.erlang.org/.
%% 
%% Software distributed under the License is distributed on an "AS IS"
%% basis, WITHOUT WARRANTY OF ANY KIND, either express or implied. See
%% the License for the specific language governing rights and limitations
%% under the License.
%% 
%% The Initial Developer of the Original Code is Ericsson Utvecklings AB.
%% Portions created by Ericsson are Copyright 1999, Ericsson Utvecklings
%% AB. All Rights Reserved.''
%% 
%%     $Id$
%%
%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
%%
%% This module administers three kinds of log files:
%%
%% 1 The transaction log
%%   mnesia_tm appends to the log (via mnesia_log) at the
%%   end of each transaction (or dirty write) and
%%   mnesia_dumper reads the log and performs the ops in
%%   the dat files. The dump_log is done  at startup and
%%   at intervals controlled by the user.
%%
%% 2 The mnesia_down log
%%   mnesia_tm appends to the log (via mnesia_log) when it
%%   realizes that mnesia goes up or down on another node.
%%   mnesia_init reads the log (via mnesia_log) at startup.
%%
%% 3 The backup log
%%   mnesia_schema produces one tiny log when the schema is
%%   initially created. mnesia_schema also reads the log
%%   when the user wants tables (possibly incl the schema)
%%   to be restored. mnesia_log appends to the log when the
%%   user wants to produce a real backup.
%%
%%   The actual access to the backup media is performed via the
%%   mnesia_backup module for both read and write. mnesia_backup
%%   uses the disk_log (*), BUT the user may write an own module
%%   with the same interface as mnesia_backup and configure
%%   Mnesia so the alternate module performs the actual accesses
%%   to the backup media. This means that the user may put the
%%   backup on medias that Mnesia does not know about possibly on
%%   hosts where Erlang is not running.
%%
%% All these logs have to some extent a common structure.
%% They are all using the disk_log module (*) for the basic
%% file structure. The disk_log has a repair feature that
%% can be used to skip erroneous log records if one comes to
%% the conclusion that it is more important to reuse some
%% of the log records than the risque of obtaining inconsistent
%% data. If the data becomes inconsistent it is solely up to the
%% application to make it consistent again. The automatic
%% reparation of the disk_log is very powerful, but use it
%% with extreme care.
%%
%% First in all Mnesia's log file is a mnesia log header.
%% It contains a list with a log_header record as single
%% element. The structure of the log_header may never be
%% changed since it may be written to very old backup files.
%% By holding this record definition stable we can be
%% able to comprahend backups from timepoint 0. It also
%% allows us to use the backup format as an interchange
%% format between Mnesia releases.
%%
%% An op-list is a list of tuples with arity 3. Each tuple
%% has this structure: {Oid, Recs, Op} where Oid is the tuple
%% {Tab, Key}, Recs is a (possibly empty) list of records and
%% Op is an atom.
%%
%% The log file structure for the transaction log is as follows.
%%
%%    After the mnesia log section follows an extended record section
%%    containing op-lists. There are several values that Op may
%%    have, such as write, delete, update_counter, delete_object,
%%    and replace. There is no special end of section marker.
%%
%%    +-----------------+
%%    | mnesia log head |
%%    +-----------------+
%%    | extended record |
%%    | section         |
%%    +-----------------+
%%
%% The log file structure for the mnesia_down log is as follows.
%%
%%    After the mnesia log section follows a mnesia_down section
%%    containg lists with yoyo records as single element.
%%
%%    +-----------------+
%%    | mnesia log head |
%%    +-----------------+
%%    | mnesia_down     |
%%    | section         |
%%    +-----------------+
%%
%% The log file structure for the backup log is as follows.
%%
%%    After the mnesia log section follows a schema section
%%    containing record lists. A record list is a list of tuples
%%    where {schema, Tab} is interpreted as a delete_table(Tab) and
%%    {schema, Tab, CreateList} are interpreted as create_table.
%%
%%    The record section also contains record lists. In this section
%%    {Tab, Key} is interpreted as delete({Tab, Key}) and other tuples
%%    as write(Tuple). There is no special end of section marker.
%%
%%    +-----------------+
%%    | mnesia log head |
%%    +-----------------+
%%    | schema section  |
%%    +-----------------+
%%    | record section  |
%%    +-----------------+
%%
%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%

-module(mnesia_log).

-export([
	 append/2,
	 backup/1,
	 backup/2,
	 backup_checkpoint/2,
	 backup_checkpoint/3,
	 backup_log_header/0,
	 backup_master/2,
	 chunk_decision_log/1,
	 chunk_decision_tab/1,
	 chunk_log/1,
	 chunk_log/2,
	 close_decision_log/0,
	 close_decision_tab/0,
	 close_log/1,
	 unsafe_close_log/1,
	 confirm_log_dump/1,
	 confirm_decision_log_dump/0,
	 previous_log_file/0,
	 previous_decision_log_file/0,
	 latest_log_file/0,
	 decision_log_version/0,
	 decision_log_file/0,
	 decision_tab_file/0,
	 decision_tab_version/0,
	 dcl_version/0,
	 dcd_version/0,
	 ets2dcd/1,
	 ets2dcd/2,
	 dcd2ets/1,
	 dcd2ets/2,
	 init/0,
	 init_log_dump/0,
	 log/1,
	 slog/1,
	 log_decision/1,
	 log_files/0,
	 open_decision_log/0,
	 trans_log_header/0,
	 open_decision_tab/0,
	 dcl_log_header/0,
	 dcd_log_header/0,
	 open_log/4,
	 open_log/6,
	 prepare_decision_log_dump/0,
	 prepare_log_dump/1,
	 save_decision_tab/1,
	 purge_all_logs/0,
	 purge_some_logs/0,
	 stop/0,
	 tab_copier/3,
	 version/0,
	 view/0,
	 view/1,
	 write_trans_log_header/0
	]).
	
	
-include("mnesia.hrl").
-import(mnesia_lib, [val/1, dir/1]).
-import(mnesia_lib, [exists/1, fatal/2, error/2, dbg_out/2]).

trans_log_header() -> log_header(trans_log, version()).
backup_log_header() -> log_header(backup_log, "1.2").
decision_log_header() -> log_header(decision_log, decision_log_version()).
decision_tab_header() -> log_header(decision_tab, decision_tab_version()).
dcl_log_header() -> log_header(dcl_log, dcl_version()).
dcd_log_header() -> log_header(dcd_log, dcd_version()).

log_header(Kind, Version) ->
    #log_header{log_version=Version,
		log_kind=Kind,
		mnesia_version=mnesia:system_info(version),
		node=node(),
		now=now()}.

version() -> "4.3".

decision_log_version() -> "3.0".

decision_tab_version() -> "1.0".

dcl_version() -> "1.0".
dcd_version() -> "1.0".
     
append(Log, Bin) when binary(Bin) ->
    disk_log:balog(Log, Bin);
append(Log, Term) ->
    disk_log:alog(Log, Term).

%% Synced append
sappend(Log, Bin) when binary(Bin) ->
    ok = disk_log:blog(Log, Bin);  
sappend(Log, Term) ->
    ok = disk_log:log(Log, Term).  

%% Write commit records to the latest_log
log(C) when  C#commit.disc_copies == [],
             C#commit.disc_only_copies  == [],
             C#commit.schema_ops == [] ->
    ignore;
log(C) ->
    case mnesia_monitor:use_dir() of
        true ->
	    if
		record(C, commit) ->
		    C2 =  C#commit{ram_copies = [], snmp = []},
		    append(latest_log, C2);
		true ->
		    %% Either a commit record as binary
		    %% or some decision related info
		    append(latest_log, C)
	    end,
	    mnesia_dumper:incr_log_writes();
	false ->
	    ignore
    end.

%% Synced

slog(C) when  C#commit.disc_copies == [],
             C#commit.disc_only_copies  == [],
             C#commit.schema_ops == [] ->
    ignore;
slog(C) ->
    case mnesia_monitor:use_dir() of
        true ->
	    if
		record(C, commit) ->
		    C2 =  C#commit{ram_copies = [], snmp = []},
		    sappend(latest_log, C2);
		true ->
		    %% Either a commit record as binary
		    %% or some decision related info
		    sappend(latest_log, C)
	    end,
	    mnesia_dumper:incr_log_writes();
	false ->
	    ignore
    end.


%% Stuff related to the file LOG

%% Returns a list of logfiles. The oldest is first.
log_files() -> [previous_log_file(),
		latest_log_file(),
		decision_tab_file()
	       ].

latest_log_file() -> dir(latest_log_name()).

previous_log_file() -> dir("PREVIOUS.LOG").

decision_log_file() -> dir(decision_log_name()).

decision_tab_file() -> dir(decision_tab_name()).
    
previous_decision_log_file() -> dir("PDECISION.LOG").

latest_log_name() -> "LATEST.LOG".

decision_log_name() -> "DECISION.LOG".

decision_tab_name() -> "DECISION_TAB.LOG".

init() ->
    case mnesia_monitor:use_dir() of
	true ->
	    Prev = previous_log_file(),
	    verify_no_exists(Prev),
	    
	    Latest = latest_log_file(),
	    verify_no_exists(Latest),
	    
	    Header = trans_log_header(),
	    open_log(latest_log, Header, Latest);
	false ->
	    ok
    end.

verify_no_exists(Fname) ->
    case exists(Fname) of
	false ->
	    ok;
	true ->
	    fatal("Log file exists: ~p~n", [Fname])
    end.

open_log(Name, Header, Fname) ->
    Exists = exists(Fname),
    open_log(Name, Header, Fname, Exists).

open_log(Name, Header, Fname, Exists) ->
    Repair = mnesia_monitor:get_env(auto_repair),
    open_log(Name, Header, Fname, Exists, Repair).

open_log(Name, Header, Fname, Exists, Repair) ->
    case Name == previous_log of
	true ->
	    open_log(Name, Header, Fname, Exists, Repair, read_only);
	false ->
	    open_log(Name, Header, Fname, Exists, Repair, read_write)
    end.

open_log(Name, Header, Fname, Exists, Repair, Mode) ->
    Args = [{file, Fname}, {name, Name}, {repair, Repair}, {mode, Mode}],
%%    io:format("~p:open_log: ~p ~p~n", [?MODULE, Name, Fname]),
    case mnesia_monitor:open_log(Args) of
	{ok, Log} when Exists == true ->
	    Log;
	{ok, Log} ->
	    write_header(Log, Header),
	    Log;
	{repaired, Log, _, {badbytes, 0}} when Exists == true ->
	    Log;
	{repaired, Log, _, {badbytes, 0}} ->
	    write_header(Log, Header),
	    Log;
	{repaired, Log, _Recover, BadBytes} ->
	    mnesia_lib:important("Data may be missing, log ~p repaired: Lost ~p bytes~n", 
				 [Fname, BadBytes]),
	    Log;
	{error, Reason} when Repair == true ->
	    file:delete(Fname),
	    mnesia_lib:important("Data may be missing, Corrupt logfile deleted: ~p, ~p ~n", 
				 [Fname, Reason]),
	    %% Create a new 
	    open_log(Name, Header, Fname, false, false, read_write);
	{error, Reason} ->
	    fatal("Cannot open log file ~p: ~p~n", [Fname, Reason])
    end.

write_header(Log, Header) -> 
    append(Log, Header).

write_trans_log_header() ->
    write_header(latest_log, trans_log_header()).

stop() ->
    case mnesia_monitor:use_dir() of
        true ->
	    close_log(latest_log);
	false ->
	    ok
    end.

close_log(Log) ->
%%    io:format("mnesia_log:close_log ~p~n", [Log]),
%%    io:format("mnesia_log:close_log ~p~n", [Log]),
    case disk_log:sync(Log) of 
	ok -> ok;
	{error, {read_only_mode, Log}} -> 
	    ok;
	{error, Reason} -> 
	    mnesia_lib:important("Failed syncing ~p to_disk reason ~p ~n", 
				 [Log, Reason])
    end,
    mnesia_monitor:close_log(Log).

unsafe_close_log(Log) ->
%%    io:format("mnesia_log:close_log ~p~n", [Log]),
    mnesia_monitor:unsafe_close_log(Log).


purge_some_logs() ->
    mnesia_monitor:unsafe_close_log(latest_log), 
    file:delete(latest_log_file()),
    file:delete(decision_tab_file()).

purge_all_logs() ->
    file:delete(previous_log_file()),
    file:delete(latest_log_file()),
    file:delete(decision_tab_file()).

%% Prepare dump by renaming the open logfile if possible
%% Returns a tuple on the following format: {Res, OpenLog}
%% where OpenLog is the file descriptor to log file, ready for append
%% and Res is one of the following: already_dumped, needs_dump or {error, Reason}
prepare_log_dump(InitBy) ->
    Diff = mnesia_dumper:get_log_writes() -
           mnesia_lib:read_counter(trans_log_writes_prev),
    if
	Diff == 0, InitBy /= startup ->
	    already_dumped;
	true ->
	    case mnesia_monitor:use_dir() of
		true ->
		    Prev = previous_log_file(),
		    prepare_prev(Diff, InitBy, Prev, exists(Prev));
		false ->
		    already_dumped
	    end
    end.

prepare_prev(Diff, _, _, true) ->
    {needs_dump, Diff};
prepare_prev(Diff, startup, Prev, false) ->
    Latest = latest_log_file(),
    case exists(Latest) of
	true ->
	    case file:rename(Latest, Prev) of
		ok ->
		    {needs_dump, Diff};
		{error, Reason} ->
		    {error, Reason}
	    end;
	false ->
	    already_dumped
    end;
prepare_prev(Diff, _InitBy, Prev, false) ->
    Head = trans_log_header(),
    case mnesia_monitor:reopen_log(latest_log, Prev, Head) of
	ok ->
	    {needs_dump, Diff};
	{error, Reason} ->
	    Latest = latest_log_file(),
	    {error, {"Cannot rename log file",
		     [Latest, Prev, Reason]}}
    end.

%% Init dump and return PrevLogFileDesc or exit.
init_log_dump() ->
    Fname = previous_log_file(),
    open_log(previous_log, trans_log_header(), Fname),
    start.


chunk_log(Cont) ->
    chunk_log(previous_log, Cont).

chunk_log(_Log, eof) ->
    eof;
chunk_log(Log, Cont) ->
    case catch disk_log:chunk(Log, Cont) of
	{error, Reason} ->
	    fatal("Possibly truncated ~p file: ~p~n",
		  [Log, Reason]);
	{C2, Chunk, _BadBytes} ->
	    %% Read_only case, should we warn about the bad log file?
	    %% BUGBUG Should we crash if Repair == false ?? 
	    %% We got to check this !!
	    mnesia_lib:important("~p repaired, lost ~p bad bytes~n", [Log, _BadBytes]),
	    {C2, Chunk}; 
	Other ->
	    Other
    end.

%% Confirms the dump by closing prev log and delete the file
confirm_log_dump(Updates) ->
    case mnesia_monitor:close_log(previous_log) of
	ok ->
	    file:delete(previous_log_file()),
	    mnesia_lib:incr_counter(trans_log_writes_prev, Updates),
	    dumped;
	{error, Reason} ->
	    {error, Reason}
    end.

%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
%% Decision log

open_decision_log() ->
    Latest = decision_log_file(),
    open_log(decision_log, decision_log_header(), Latest),
    start.
    
prepare_decision_log_dump() ->
    Prev = previous_decision_log_file(),
    prepare_decision_log_dump(exists(Prev), Prev).

prepare_decision_log_dump(false, Prev) ->
    Head = decision_log_header(),
    case mnesia_monitor:reopen_log(decision_log, Prev, Head) of
	ok ->
	    prepare_decision_log_dump(true, Prev);
	{error, Reason} ->
	    fatal("Cannot rename decision log file ~p -> ~p: ~p~n",
		     [decision_log_file(), Prev, Reason])
    end;
prepare_decision_log_dump(true, Prev) ->
    open_log(previous_decision_log, decision_log_header(), Prev),
    start.

chunk_decision_log(Cont) ->
    %% dbg_out("chunk log ~p~n", [Cont]),
    chunk_log(previous_decision_log, Cont).

%% Confirms dump of the decision log