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rdf_persistency.pl
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rdf_persistency.pl
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/* Part of SWI-Prolog
Author: Jan Wielemaker
E-mail: [email protected]
WWW: http://www.swi-prolog.org
Copyright (c) 2006-2015, University of Amsterdam
VU University Amsterdam
All rights reserved.
Redistribution and use in source and binary forms, with or without
modification, are permitted provided that the following conditions
are met:
1. Redistributions of source code must retain the above copyright
notice, this list of conditions and the following disclaimer.
2. Redistributions in binary form must reproduce the above copyright
notice, this list of conditions and the following disclaimer in
the documentation and/or other materials provided with the
distribution.
THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
"AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS
FOR A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE
COPYRIGHT OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT,
INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING,
BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES;
LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER
CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN
ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE
POSSIBILITY OF SUCH DAMAGE.
*/
:- module(rdf_persistency,
[ rdf_attach_db/2, % +Directory, +Options
rdf_detach_db/0, % +Detach current Graph
rdf_current_db/1, % -Directory
rdf_persistency/2, % +Graph, +Bool
rdf_flush_journals/1, % +Options
rdf_persistency_property/1, % ?Property
rdf_journal_file/2, % ?Graph, ?JournalFile
rdf_snapshot_file/2, % ?Graph, ?SnapshotFile
rdf_db_to_file/2 % ?Graph, ?FileBase
]).
:- use_module(library(semweb/rdf_db),
[ rdf_graph/1, rdf_unload_graph/1, rdf_statistics/1,
rdf_load_db/1, rdf_retractall/4, rdf_create_graph/1,
rdf_assert/4, rdf_update/5, rdf_monitor/2, rdf/4,
rdf_save_db/2, rdf_atom_md5/3, rdf_current_ns/2,
rdf_register_ns/3
]).
:- autoload(library(apply),[maplist/2,maplist/3,partition/4,exclude/3]).
:- use_module(library(debug),[debug/3]).
:- autoload(library(error),
[permission_error/3,must_be/2,domain_error/2]).
:- autoload(library(filesex),
[directory_file_path/3,make_directory_path/1]).
:- autoload(library(lists),[select/3,append/3]).
:- autoload(library(option),[option/2,option/3]).
:- autoload(library(readutil),[read_file_to_terms/3]).
:- autoload(library(socket),[gethostname/1]).
:- autoload(library(thread),[concurrent/3]).
:- autoload(library(uri),[uri_encoded/3]).
/** <module> RDF persistency plugin
This module provides persistency for rdf_db.pl based on the
rdf_monitor/2 predicate to track changes to the repository. Where
previous versions used autosafe of the whole database using the
quick-load format of rdf_db, this version is based on a quick-load file
per source (4th argument of rdf/4), and journalling for edit operations.
The result is safe, avoids frequent small changes to large files which
makes synchronisation and backup expensive and avoids long disruption of
the server doing the autosafe. Only loading large files disrupts service
for some time.
The persistent backup of the database is realised in a directory, using
a lock file to avoid corruption due to concurrent access. Each source is
represented by two files, the latest snapshot and a journal. The state
is restored by loading the snapshot and replaying the journal. The
predicate rdf_flush_journals/1 can be used to create fresh snapshots and
delete the journals.
@tbd If there is a complete `.new' snapshot and no journal, we should
move the .new to the plain snapshot name as a means of recovery.
@tbd Backup of each graph using one or two files is very costly if there
are many graphs. Although the currently used subdirectories avoid
hitting OS limits early, this is still not ideal. Probably we
should collect (small, older?) files and combine them into a single
quick load file. We could call this (similar to GIT) a `pack'.
@see rdf_edit.pl
*/
:- volatile
rdf_directory/1,
rdf_lock/2,
rdf_option/1,
source_journal_fd/2,
file_base_db/2.
:- dynamic
rdf_directory/1, % Absolute path
rdf_lock/2, % Dir, Lock
rdf_option/1, % Defined options
source_journal_fd/2, % DB, JournalFD
file_base_db/2. % FileBase, DB
:- meta_predicate
no_agc(0).
:- predicate_options(rdf_attach_db/2, 2,
[ access(oneof([read_write,read_only])),
concurrency(positive_integer),
max_open_journals(positive_integer),
silent(oneof([true,false,brief])),
log_nested_transactions(boolean)
]).
%! rdf_attach_db(+Directory, +Options) is det.
%
% Start persistent operations using Directory as place to store
% files. There are several cases:
%
% * Empty DB, existing directory
% Load the DB from the existing directory
%
% * Full DB, empty directory
% Create snapshots for all sources in directory
%
% Options:
%
% * access(+AccessMode)
% One of =auto= (default), =read_write= or
% =read_only=. Read-only access implies that the RDF
% store is not locked. It is read at startup and all
% modifications to the data are temporary. The default
% =auto= mode is =read_write= if the directory is
% writeable and the lock can be acquired. Otherwise
% it reverts to =read_only=.
%
% * concurrency(+Jobs)
% Number of threads to use for loading the initial
% database. If not provided it is the number of CPUs
% as obtained from the flag =cpu_count=.
%
% * max_open_journals(+Count)
% Maximum number of journals kept open. If not provided,
% the default is 10. See limit_fd_pool/0.
%
% * directory_levels(+Count)
% Number of levels of intermediate directories for storing
% the graph files. Default is 2.
%
% * silent(+BoolOrBrief)
% If =true= (default =false=), do not print informational
% messages. Finally, if =brief= it will show minimal
% feedback.
%
% * log_nested_transactions(+Boolean)
% If =true=, nested _log_ transactions are added to the
% journal information. By default (=false=), no log-term
% is added for nested transactions.\\
%
% @error existence_error(source_sink, Directory)
% @error permission_error(write, directory, Directory)
rdf_attach_db(DirSpec, Options) :-
option(access(read_only), Options),
!,
absolute_file_name(DirSpec,
Directory,
[ access(read),
file_type(directory)
]),
rdf_attach_db_ro(Directory, Options).
rdf_attach_db(DirSpec, Options) :-
option(access(read_write), Options),
!,
rdf_attach_db_rw(DirSpec, Options).
rdf_attach_db(DirSpec, Options) :-
absolute_file_name(DirSpec,
Directory,
[ access(exist),
file_type(directory),
file_errors(fail)
]),
!,
( access_file(Directory, write)
-> catch(rdf_attach_db_rw(Directory, Options), E, true),
( var(E)
-> true
; E = error(permission_error(lock, rdf_db, _), _)
-> print_message(warning, E),
print_message(warning, rdf(read_only)),
rdf_attach_db(DirSpec, [access(read_only)|Options])
; throw(E)
)
; print_message(warning,
error(permission_error(write, directory, Directory))),
print_message(warning, rdf(read_only)),
rdf_attach_db_ro(Directory, Options)
).
rdf_attach_db(DirSpec, Options) :-
catch(rdf_attach_db_rw(DirSpec, Options), E, true),
( var(E)
-> true
; print_message(warning, E),
print_message(warning, rdf(read_only)),
rdf_attach_db(DirSpec, [access(read_only)|Options])
).
rdf_attach_db_rw(DirSpec, Options) :-
absolute_file_name(DirSpec,
Directory,
[ access(write),
file_type(directory),
file_errors(fail)
]),
!,
( rdf_directory(Directory)
-> true % update settings?
; rdf_detach_db,
mkdir(Directory),
lock_db(Directory),
assert(rdf_directory(Directory)),
assert_options(Options),
stop_monitor, % make sure not to register load
no_agc(load_db),
at_halt(rdf_detach_db),
start_monitor
).
rdf_attach_db_rw(DirSpec, Options) :-
absolute_file_name(DirSpec,
Directory,
[ solutions(all)
]),
( exists_directory(Directory)
-> access_file(Directory, write)
; catch(make_directory(Directory), _, fail)
),
!,
rdf_attach_db(Directory, Options).
rdf_attach_db_rw(DirSpec, _) :- % Generate an existence or
absolute_file_name(DirSpec, % permission error
Directory,
[ access(exist),
file_type(directory)
]),
permission_error(write, directory, Directory).
%! rdf_attach_db_ro(+Directory, +Options)
%
% Open an RDF database in read-only mode.
rdf_attach_db_ro(Directory, Options) :-
rdf_detach_db,
assert(rdf_directory(Directory)),
assert_options(Options),
stop_monitor, % make sure not to register load
no_agc(load_db).
assert_options([]).
assert_options([H|T]) :-
( option_type(H, Check)
-> Check,
assert(rdf_option(H))
; true % ignore options we do not understand
),
assert_options(T).
option_type(concurrency(X), must_be(positive_integer, X)).
option_type(max_open_journals(X), must_be(positive_integer, X)).
option_type(directory_levels(X), must_be(positive_integer, X)).
option_type(silent(X), must_be(oneof([true,false,brief]), X)).
option_type(log_nested_transactions(X), must_be(boolean, X)).
option_type(access(X), must_be(oneof([read_write,
read_only]), X)).
%! rdf_persistency_property(?Property) is nondet.
%
% True when Property is a property of the current persistent database.
% Exposes the properties that can be passed as options to
% rdf_attach_db/2. Specifically,
% rdf_persistency_property(access(read_only)) is true iff the database
% is mounted in read-only mode. In addition, the following property is
% supported:
%
% - directory(Dir)
% The directory in which the database resides.
rdf_persistency_property(Property) :-
var(Property),
!,
rdf_persistency_property_(Property).
rdf_persistency_property(Property) :-
rdf_persistency_property_(Property),
!.
rdf_persistency_property_(Property) :-
rdf_option(Property).
rdf_persistency_property_(directory(Dir)) :-
rdf_directory(Dir).
%! no_agc(:Goal)
%
% Run Goal with atom garbage collection disabled. Loading an RDF
% database creates large amounts of atoms we *know* are not
% garbage.
no_agc(Goal) :-
current_prolog_flag(agc_margin, Old),
setup_call_cleanup(
set_prolog_flag(agc_margin, 0),
Goal,
set_prolog_flag(agc_margin, Old)).
%! rdf_detach_db is det.
%
% Detach from the current database. Succeeds silently if no
% database is attached. Normally called at the end of the program
% through at_halt/1.
rdf_detach_db :-
debug(halt, 'Detaching RDF database', []),
stop_monitor,
close_journals,
( retract(rdf_directory(Dir))
-> debug(halt, 'DB Directory: ~w', [Dir]),
save_prefixes(Dir),
retractall(rdf_option(_)),
retractall(source_journal_fd(_,_)),
unlock_db(Dir)
; true
).
%! rdf_current_db(?Dir)
%
% True if Dir is the current RDF persistent database.
rdf_current_db(Directory) :-
rdf_directory(Dir),
!,
Dir = Directory.
%! rdf_flush_journals(+Options)
%
% Flush dirty journals. Options:
%
% * min_size(+KB)
% Only flush if journal is over KB in size.
% * graph(+Graph)
% Only flush the journal of Graph
%
% @tbd Provide a default for min_size?
rdf_flush_journals(Options) :-
option(graph(Graph), Options, _),
forall(rdf_graph(Graph),
rdf_flush_journal(Graph, Options)).
rdf_flush_journal(Graph, Options) :-
db_files(Graph, _SnapshotFile, JournalFile),
db_file(JournalFile, File),
( \+ exists_file(File)
-> true
; memberchk(min_size(KB), Options),
size_file(File, Size),
Size / 1024 < KB
-> true
; create_db(Graph)
).
/*******************************
* LOAD *
*******************************/
%! load_db is det.
%
% Reload database from the directory specified by rdf_directory/1.
% First we find all names graphs using find_dbs/1 and then we load
% them.
load_db :-
rdf_directory(Dir),
concurrency(Jobs),
cpu_stat_key(Jobs, StatKey),
get_time(Wall0),
statistics(StatKey, T0),
load_prefixes(Dir),
verbosity(Silent),
find_dbs(Dir, Graphs, SnapShots, Journals),
length(Graphs, GraphCount),
maplist(rdf_unload_graph, Graphs),
rdf_statistics(triples(Triples0)),
load_sources(snapshots, SnapShots, Silent, Jobs),
load_sources(journals, Journals, Silent, Jobs),
rdf_statistics(triples(Triples1)),
statistics(StatKey, T1),
get_time(Wall1),
T is T1 - T0,
Wall is Wall1 - Wall0,
Triples = Triples1 - Triples0,
message_level(Silent, Level),
print_message(Level, rdf(restore(attached(GraphCount, Triples, T/Wall)))).
load_sources(_, [], _, _) :- !.
load_sources(Type, Sources, Silent, Jobs) :-
length(Sources, Count),
RunJobs is min(Count, Jobs),
print_message(informational, rdf(restoring(Type, Count, RunJobs))),
make_goals(Sources, Silent, 1, Count, Goals),
concurrent(RunJobs, Goals, []).
%! make_goals(+DBs, +Silent, +Index, +Total, -Goals)
make_goals([], _, _, _, []).
make_goals([DB|T0], Silent, I, Total,
[load_source(DB, Silent, I, Total)|T]) :-
I2 is I + 1,
make_goals(T0, Silent, I2, Total, T).
verbosity(Silent) :-
rdf_option(silent(Silent)),
!.
verbosity(Silent) :-
current_prolog_flag(verbose, silent),
!,
Silent = true.
verbosity(brief).
%! concurrency(-Jobs)
%
% Number of jobs to run concurrently.
concurrency(Jobs) :-
rdf_option(concurrency(Jobs)),
!.
concurrency(Jobs) :-
current_prolog_flag(cpu_count, Jobs),
Jobs > 0,
!.
concurrency(1).
cpu_stat_key(1, cputime) :- !.
cpu_stat_key(_, process_cputime).
%! find_dbs(+Dir, -Graphs, -SnapBySize, -JournalBySize) is det.
%
% Scan the persistent database and return a list of snapshots and
% journals, both sorted by file-size. Each term is of the form
%
% ==
% db(Size, Ext, DB, DBFile, Depth)
% ==
find_dbs(Dir, Graphs, SnapBySize, JournalBySize) :-
directory_files(Dir, Files),
phrase(scan_db_files(Files, Dir, '.', 0), Scanned),
maplist(db_graph, Scanned, UnsortedGraphs),
sort(UnsortedGraphs, Graphs),
( consider_reindex_db(Dir, Graphs, Scanned)
-> find_dbs(Dir, Graphs, SnapBySize, JournalBySize)
; partition(db_is_snapshot, Scanned, Snapshots, Journals),
sort(Snapshots, SnapBySize),
sort(Journals, JournalBySize)
).
consider_reindex_db(Dir, Graphs, Scanned) :-
length(Graphs, Count),
Count > 0,
DepthNeeded is floor(log(Count)/log(256)),
( maplist(depth_db(DepthNow), Scanned)
-> ( DepthNeeded > DepthNow
-> true
; retractall(rdf_option(directory_levels(_))),
assertz(rdf_option(directory_levels(DepthNow))),
fail
)
; true
),
reindex_db(Dir, DepthNeeded).
db_is_snapshot(Term) :-
arg(2, Term, trp).
db_graph(Term, DB) :-
arg(3, Term, DB).
db_file_name(Term, File) :-
arg(4, Term, File).
depth_db(Depth, DB) :-
arg(5, DB, Depth).
%! scan_db_files(+Files, +Dir, +Prefix, +Depth)// is det.
%
% Produces a list of db(DB, Size, File) for all recognised RDF
% database files. File is relative to the database directory Dir.
scan_db_files([], _, _, _) -->
[].
scan_db_files([Nofollow|T], Dir, Prefix, Depth) -->
{ nofollow(Nofollow) },
!,
scan_db_files(T, Dir, Prefix, Depth).
scan_db_files([File|T], Dir, Prefix, Depth) -->
{ file_name_extension(Base, Ext, File),
db_extension(Ext),
!,
rdf_db_to_file(DB, Base),
directory_file_path(Prefix, File, DBFile),
directory_file_path(Dir, DBFile, AbsFile),
size_file(AbsFile, Size)
},
[ db(Size, Ext, DB, AbsFile, Depth) ],
scan_db_files(T, Dir, Prefix, Depth).
scan_db_files([D|T], Dir, Prefix, Depth) -->
{ directory_file_path(Prefix, D, SubD),
directory_file_path(Dir, SubD, AbsD),
exists_directory(AbsD),
\+ read_link(AbsD, _, _), % Do not follow links
!,
directory_files(AbsD, SubFiles),
SubDepth is Depth + 1
},
scan_db_files(SubFiles, Dir, SubD, SubDepth),
scan_db_files(T, Dir, Prefix, Depth).
scan_db_files([_|T], Dir, Prefix, Depth) -->
scan_db_files(T, Dir, Prefix, Depth).
nofollow(.).
nofollow(..).
db_extension(trp).
db_extension(jrn).
:- public load_source/4. % called through make_goals/5
load_source(DB, Silent, Nth, Total) :-
db_file_name(DB, File),
db_graph(DB, Graph),
message_level(Silent, Level),
graph_triple_count(Graph, Count0),
statistics(cputime, T0),
( db_is_snapshot(DB)
-> print_message(Level, rdf(restore(Silent, snapshot(Graph, File)))),
rdf_load_db(File)
; print_message(Level, rdf(restore(Silent, journal(Graph, File)))),
load_journal(File, Graph)
),
statistics(cputime, T1),
T is T1 - T0,
graph_triple_count(Graph, Count1),
Count is Count1 - Count0,
print_message(Level, rdf(restore(Silent,
done(Graph, T, Count, Nth, Total)))).
graph_triple_count(Graph, Count) :-
rdf_statistics(triples_by_graph(Graph, Count)),
!.
graph_triple_count(_, 0).
%! attach_graph(+Graph, +Options) is det.
%
% Load triples and reload journal from the indicated snapshot
% file.
attach_graph(Graph, Options) :-
( option(silent(true), Options)
-> Level = silent
; Level = informational
),
db_files(Graph, SnapshotFile, JournalFile),
rdf_retractall(_,_,_,Graph),
statistics(cputime, T0),
print_message(Level, rdf(restore(Silent, Graph))),
db_file(SnapshotFile, AbsSnapShot),
( exists_file(AbsSnapShot)
-> print_message(Level, rdf(restore(Silent, snapshot(SnapshotFile)))),
rdf_load_db(AbsSnapShot)
; true
),
( exists_db(JournalFile)
-> print_message(Level, rdf(restore(Silent, journal(JournalFile)))),
load_journal(JournalFile, Graph)
; true
),
statistics(cputime, T1),
T is T1 - T0,
( rdf_statistics(triples_by_graph(Graph, Count))
-> true
; Count = 0
),
print_message(Level, rdf(restore(Silent,
done(Graph, T, Count)))).
message_level(true, silent) :- !.
message_level(_, informational).
/*******************************
* LOAD JOURNAL *
*******************************/
%! load_journal(+File:atom, +DB:atom) is det.
%
% Process transactions from the RDF journal File, adding the given
% named graph.
load_journal(File, DB) :-
rdf_create_graph(DB),
setup_call_cleanup(
open(File, read, In, [encoding(utf8)]),
( read(In, T0),
process_journal(T0, In, DB)
),
close(In)).
process_journal(end_of_file, _, _) :- !.
process_journal(Term, In, DB) :-
( process_journal_term(Term, DB)
-> true
; throw(error(type_error(journal_term, Term), _))
),
read(In, T2),
process_journal(T2, In, DB).
process_journal_term(assert(S,P,O), DB) :-
rdf_assert(S,P,O,DB).
process_journal_term(assert(S,P,O,Line), DB) :-
rdf_assert(S,P,O,DB:Line).
process_journal_term(retract(S,P,O), DB) :-
rdf_retractall(S,P,O,DB).
process_journal_term(retract(S,P,O,Line), DB) :-
rdf_retractall(S,P,O,DB:Line).
process_journal_term(update(S,P,O,Action), DB) :-
( rdf_update(S,P,O,DB, Action)
-> true
; print_message(warning, rdf(update_failed(S,P,O,Action)))
).
process_journal_term(start(_), _). % journal open/close
process_journal_term(end(_), _).
process_journal_term(begin(_), _). % logged transaction (compatibility)
process_journal_term(end, _).
process_journal_term(begin(_,_,_,_), _). % logged transaction (current)
process_journal_term(end(_,_,_), _).
/*******************************
* CREATE JOURNAL *
*******************************/
:- dynamic
blocked_db/2, % DB, Reason
transaction_message/3, % Nesting, Time, Message
transaction_db/3. % Nesting, DB, Id
%! rdf_persistency(+DB, Bool)
%
% Specify whether a database is persistent. Switching to =false=
% kills the persistent state. Switching to =true= creates it.
rdf_persistency(DB, Bool) :-
must_be(atom, DB),
must_be(boolean, Bool),
fail.
rdf_persistency(DB, false) :-
!,
( blocked_db(DB, persistency)
-> true
; assert(blocked_db(DB, persistency)),
delete_db(DB)
).
rdf_persistency(DB, true) :-
( retract(blocked_db(DB, persistency))
-> create_db(DB)
; true
).
%! rdf_db:property_of_graph(?Property, +Graph) is nondet.
%
% Extend rdf_graph_property/2 with new properties.
:- multifile
rdf_db:property_of_graph/2.
rdf_db:property_of_graph(persistent(State), Graph) :-
( blocked_db(Graph, persistency)
-> State = false
; State = true
).
%! start_monitor is det.
%! stop_monitor is det.
%
% Start/stop monitoring the RDF database for changes and update
% the journal.
start_monitor :-
rdf_monitor(monitor,
[ -assert(load)
]).
stop_monitor :-
rdf_monitor(monitor,
[ -all
]).
%! monitor(+Term) is semidet.
%
% Handle an rdf_monitor/2 callback to deal with persistency. Note
% that the monitor calls that come from rdf_db.pl that deal with
% database changes are serialized. They do come from different
% threads though.
monitor(Msg) :-
debug(monitor, 'Monitor: ~p~n', [Msg]),
fail.
monitor(assert(S,P,O,DB:Line)) :-
!,
\+ blocked_db(DB, _),
journal_fd(DB, Fd),
open_transaction(DB, Fd),
format(Fd, '~q.~n', [assert(S,P,O,Line)]),
sync_journal(DB, Fd).
monitor(assert(S,P,O,DB)) :-
\+ blocked_db(DB, _),
journal_fd(DB, Fd),
open_transaction(DB, Fd),
format(Fd, '~q.~n', [assert(S,P,O)]),
sync_journal(DB, Fd).
monitor(retract(S,P,O,DB:Line)) :-
!,
\+ blocked_db(DB, _),
journal_fd(DB, Fd),
open_transaction(DB, Fd),
format(Fd, '~q.~n', [retract(S,P,O,Line)]),
sync_journal(DB, Fd).
monitor(retract(S,P,O,DB)) :-
\+ blocked_db(DB, _),
journal_fd(DB, Fd),
open_transaction(DB, Fd),
format(Fd, '~q.~n', [retract(S,P,O)]),
sync_journal(DB, Fd).
monitor(update(S,P,O,DB:Line,Action)) :-
!,
\+ blocked_db(DB, _),
( Action = graph(NewDB)
-> monitor(assert(S,P,O,NewDB)),
monitor(retract(S,P,O,DB:Line))
; journal_fd(DB, Fd),
format(Fd, '~q.~n', [update(S,P,O,Action)]),
sync_journal(DB, Fd)
).
monitor(update(S,P,O,DB,Action)) :-
\+ blocked_db(DB, _),
( Action = graph(NewDB)
-> monitor(assert(S,P,O,NewDB)),
monitor(retract(S,P,O,DB))
; journal_fd(DB, Fd),
open_transaction(DB, Fd),
format(Fd, '~q.~n', [update(S,P,O,Action)]),
sync_journal(DB, Fd)
).
monitor(load(BE, _DumpFileURI)) :-
( BE = end(Graphs)
-> sync_loaded_graphs(Graphs)
; true
).
monitor(create_graph(Graph)) :-
\+ blocked_db(Graph, _),
journal_fd(Graph, Fd),
open_transaction(Graph, Fd),
sync_journal(Graph, Fd).
monitor(reset) :-
forall(rdf_graph(Graph), delete_db(Graph)).
% TBD: Remove empty directories?
monitor(transaction(BE, Id)) :-
monitor_transaction(Id, BE).
monitor_transaction(load_journal(DB), begin(_)) :-
!,
assert(blocked_db(DB, journal)).
monitor_transaction(load_journal(DB), end(_)) :-
!,
retractall(blocked_db(DB, journal)).
monitor_transaction(parse(URI), begin(_)) :-
!,
( blocked_db(URI, persistency)
-> true
; assert(blocked_db(URI, parse))
).
monitor_transaction(parse(URI), end(_)) :-
!,
( retract(blocked_db(URI, parse))
-> create_db(URI)
; true
).
monitor_transaction(unload(DB), begin(_)) :-
!,
( blocked_db(DB, persistency)
-> true
; assert(blocked_db(DB, unload))
).
monitor_transaction(unload(DB), end(_)) :-
!,
( retract(blocked_db(DB, unload))
-> delete_db(DB)
; true
).
monitor_transaction(log(Msg), begin(N)) :-
!,
check_nested(N),
get_time(Time),
asserta(transaction_message(N, Time, Msg)).
monitor_transaction(log(_), end(N)) :-
check_nested(N),
retract(transaction_message(N, _, _)),
!,
findall(DB:Id, retract(transaction_db(N, DB, Id)), DBs),
end_transactions(DBs, N).
monitor_transaction(log(Msg, DB), begin(N)) :-
!,
check_nested(N),
get_time(Time),
asserta(transaction_message(N, Time, Msg)),
journal_fd(DB, Fd),
open_transaction(DB, Fd).
monitor_transaction(log(Msg, _DB), end(N)) :-
monitor_transaction(log(Msg), end(N)).
%! check_nested(+Level) is semidet.
%
% True if we must log this transaction. This is always the case
% for toplevel transactions. Nested transactions are only logged
% if log_nested_transactions(true) is defined.
check_nested(0) :- !.
check_nested(_) :-
rdf_option(log_nested_transactions(true)).
%! open_transaction(+DB, +Fd) is det.
%
% Add a begin(Id, Level, Time, Message) term if a transaction
% involves DB. Id is an incremental integer, where each database
% has its own counter. Level is the nesting level, Time is a floating
% point timestamp and Message is the message provided as argument to
% the log message.
open_transaction(DB, Fd) :-
transaction_message(N, Time, Msg),
!,
( transaction_db(N, DB, _)
-> true
; next_transaction_id(DB, Id),
assert(transaction_db(N, DB, Id)),
RoundedTime is round(Time*100)/100,
format(Fd, '~q.~n', [begin(Id, N, RoundedTime, Msg)])
).
open_transaction(_,_).
%! next_transaction_id(+DB, -Id) is det.
%
% Id is the number to user for the next logged transaction on DB.
% Transactions in each named graph are numbered in sequence.
% Searching the Id of the last transaction is performed by the 2nd
% clause starting 1Kb from the end and doubling this offset each
% failure.
:- dynamic
current_transaction_id/2.
next_transaction_id(DB, Id) :-
retract(current_transaction_id(DB, Last)),
!,
Id is Last + 1,
assert(current_transaction_id(DB, Id)).
next_transaction_id(DB, Id) :-
db_files(DB, _, Journal),
exists_file(Journal),
!,
size_file(Journal, Size),
open_db(Journal, read, In, []),
call_cleanup(iterative_expand(In, Size, Last), close(In)),
Id is Last + 1,
assert(current_transaction_id(DB, Id)).
next_transaction_id(DB, 1) :-
assert(current_transaction_id(DB, 1)).
iterative_expand(_, 0, 0) :- !.
iterative_expand(In, Size, Last) :- % Scan growing sections from the end
Max is floor(log(Size)/log(2)),
between(10, Max, Step),
Offset is -(1<<Step),
seek(In, Offset, eof, _),
skip(In, 10), % records are line-based
read(In, T0),
last_transaction_id(T0, In, 0, Last),
Last > 0,
!.
iterative_expand(In, _, Last) :- % Scan the whole file
seek(In, 0, bof, _),
read(In, T0),
last_transaction_id(T0, In, 0, Last).
last_transaction_id(end_of_file, _, Last, Last) :- !.
last_transaction_id(end(Id, _, _), In, _, Last) :-
read(In, T1),
last_transaction_id(T1, In, Id, Last).
last_transaction_id(_, In, Id, Last) :-
read(In, T1),
last_transaction_id(T1, In, Id, Last).
%! end_transactions(+DBs:list(atom:id)) is det.
%
% End a transaction that affected the given list of databases. We
% write the list of other affected databases as an argument to the
% end-term to facilitate fast finding of the related transactions.
%
% In each database, the transaction is ended with a term end(Id,
% Nesting, Others), where Id and Nesting are the transaction
% identifier and nesting (see open_transaction/2) and Others is a
% list of DB:Id, indicating other databases affected by the
% transaction.
end_transactions(DBs, N) :-
end_transactions(DBs, DBs, N).
end_transactions([], _, _).
end_transactions([DB:Id|T], DBs, N) :-
journal_fd(DB, Fd),
once(select(DB:Id, DBs, Others)),
format(Fd, 'end(~q, ~q, ~q).~n', [Id, N, Others]),
sync_journal(DB, Fd),
end_transactions(T, DBs, N).
%! sync_loaded_graphs(+Graphs)
%
% Called after a binary triple has been loaded that added triples
% to the given graphs.
sync_loaded_graphs(Graphs) :-
maplist(create_db, Graphs).
/*******************************
* JOURNAL FILES *
*******************************/
%! journal_fd(+DB, -Stream) is det.
%
% Get an open stream to a journal. If the journal is not open, old
% journals are closed to satisfy the =max_open_journals= option.
% Then the journal is opened in =append= mode. Journal files are
% always encoded as UTF-8 for portability as well as to ensure
% full coverage of Unicode.
journal_fd(DB, Fd) :-
source_journal_fd(DB, Fd),
!.
journal_fd(DB, Fd) :-
with_mutex(rdf_journal_file,
journal_fd_(DB, Out)),
Fd = Out.
journal_fd_(DB, Fd) :-
source_journal_fd(DB, Fd),
!.
journal_fd_(DB, Fd) :-
limit_fd_pool,
db_files(DB, _Snapshot, Journal),
open_db(Journal, append, Fd,
[ close_on_abort(false)
]),
time_stamp(Now),
format(Fd, '~q.~n', [start([time(Now)])]),
assert(source_journal_fd(DB, Fd)). % new one at the end