1disk_log(3) Erlang Module Definition disk_log(3)
2
6 disk_log - A disk-based term logging facility.
7
9 disk_log is a disk-based term logger that enables efficient logging of
10 items on files.
11 Two types of logs are supported:
13 halt logs:
15 Appends items to a single file, which size can be limited by the
16 disk_log module.
17 wrap logs:
19 Uses a sequence of wrap log files of limited size. As a wrap log
20 file is filled up, further items are logged on to the next file in
21 the sequence, starting all over with the first file when the last
22 file is filled up.
23 For efficiency reasons, items are always written to files as binaries.
25 Two formats of the log files are supported:
27 internal format:
29 Supports automatic repair of log files that are not properly closed
30 and enables efficient reading of logged items in chunks using a set
31 of functions defined in this module. This is the only way to read
32 internally formatted logs. An item logged to an internally format‐
33 ted log must not occupy more than 4 GB of disk space (the size must
34 fit in 4 bytes).
35 external format:
37 Leaves it up to the user to read and interpret the logged data. The
38 disk_log module cannot repair externally formatted logs.
39 For each open disk log, one process handles requests made to the disk
41 log. This process is created when open/1 is called, provided there
42 exists no process handling the disk log. A process that opens a disk
43 log can be an owner or an anonymous user of the disk log. Each owner is
44 linked to the disk log process, and an owner can close the disk log
45 either explicitly (by calling close/1 or lclose/1,2) or by terminating.
46 Owners can subscribe to notifications, messages of the form {disk_log,
48 Node, Log, Info}, which are sent from the disk log process when certain
49 events occur, see the functions and in particular the open/1 option
50 notify. A log can have many owners, but a process cannot own a log more
51 than once. However, the same process can open the log as a user more
52 than once.
53 For a disk log process to close its file properly and terminate, it
55 must be closed by its owners and once by some non-owner process for
56 each time the log was used anonymously. The users are counted and there
57 must not be any users left when the disk log process terminates.
58 Items can be logged synchronously by using functions log/2, blog/2,
60 log_terms/2, and blog_terms/2. For each of these functions, the caller
61 is put on hold until the items are logged (but not necessarily written,
62 use sync/1 to ensure that). By adding an a to each of the mentioned
63 function names, we get functions that log items asynchronously. Asyn‐
64 chronous functions do not wait for the disk log process to write the
65 items to the file, but return the control to the caller more or less
66 immediately.
67 When using the internal format for logs, use functions log/2,
69 log_terms/2, alog/2, and alog_terms/2. These functions log one or more
70 Erlang terms. By prefixing each of the functions with a b (for
71 "binary"), we get the corresponding blog() functions for the external
72 format. These functions log one or more chunks of bytes. For example,
73 to log the string "hello" in ASCII format, you can use
74 disk_log:blog(Log, "hello"), or disk_log:blog(Log,
75 list_to_binary("hello")). The two alternatives are equally efficient.
76 The blog() functions can also be used for internally formatted logs,
78 but in this case they must be called with binaries constructed with
79 calls to term_to_binary/1. There is no check to ensure this, it is
80 entirely the responsibility of the caller. If these functions are
81 called with binaries that do not correspond to Erlang terms, the
82 chunk/2,3 and automatic repair functions fail. The corresponding terms
83 (not the binaries) are returned when chunk/2,3 is called.
84 A collection of open disk logs with the same name running on different
86 nodes is said to be a distributed disk log if requests made to any of
87 the logs are automatically made to the other logs as well. The members
88 of such a collection are called individual distributed disk logs, or
89 just distributed disk logs if there is no risk of confusion. There is
90 no order between the members of such a collection. For example, logged
91 terms are not necessarily written to the node where the request was
92 made before written to the other nodes. However, a few functions do not
93 make requests to all members of distributed disk logs, namely info/1,
94 chunk/2,3, bchunk/2,3, chunk_step/3, and lclose/1,2.
95 An open disk log that is not a distributed disk log is said to be a
97 local disk log. A local disk log is only accessible from the node where
98 the disk log process runs, whereas a distributed disk log is accessible
99 from all nodes in the Erlang system, except for those nodes where a
100 local disk log with the same name as the distributed disk log exists.
101 All processes on nodes that have access to a local or distributed disk
102 log can log items or otherwise change, inspect, or close the log.
103 It is not guaranteed that all log files of a distributed disk log con‐
105 tain the same log items. No attempt is made to synchronize the contents
106 of the files. However, as long as at least one of the involved nodes is
107 alive at each time, all items are logged. When logging items to a dis‐
108 tributed log, or otherwise trying to change the log, the replies from
109 individual logs are ignored. If all nodes are down, the disk log func‐
110 tions reply with a nonode error.
111 Note:
113 In some applications, it can be unacceptable that replies from individ‐
114 ual logs are ignored. An alternative in such situations is to use many
115 local disk logs instead of one distributed disk log, and implement the
116 distribution without use of the disk_log module.
117 Errors are reported differently for asynchronous log attempts and other
120 uses of the disk_log module. When used synchronously, this module
121 replies with an error message, but when called asynchronously, this
122 module does not know where to send the error message. Instead, owners
123 subscribing to notifications receive an error_status message.
124 The disk_log module does not report errors to the error_logger module.
126 It is up to the caller to decide whether to employ the error logger.
127 Function format_error/1 can be used to produce readable messages from
128 error replies. However, information events are sent to the error logger
129 in two situations, namely when a log is repaired, or when a file is
130 missing while reading chunks.
131 Error message no_such_log means that the specified disk log is not
133 open. Nothing is said about whether the disk log files exist or not.
134 Note:
136 If an attempt to reopen or truncate a log fails (see reopen/2,3 and
137 truncate/1,2) the disk log process terminates immediately. Before the
138 process terminates, links to owners and blocking processes (see
139 block/1,2) are removed. The effect is that the links work in one direc‐
140 tion only. Any process using a disk log must check for error message
141 no_such_log if some other process truncates or reopens the log simulta‐
142 neously.
143
146 log() = term()
147 dlog_size() =
149 infinity |
150 integer() >= 1 |
151 {MaxNoBytes :: integer() >= 1, MaxNoFiles :: integer() >= 1}
152 dlog_format() = external | internal
154 dlog_head_opt() = none | term() | iodata()
156 dlog_mode() = read_only | read_write
158 dlog_type() = halt | wrap
160 continuation()
162 Chunk continuation returned by chunk/2,3, bchunk/2,3, or
164 chunk_step/3.
165 invalid_header() = term()
167 file_error() = term()
169
171 accessible_logs() -> {[LocalLog], [DistributedLog]}
172 Types:
174 LocalLog = DistributedLog = log()
176 Returns the names of the disk logs accessible on the current
178 node. The first list contains local disk logs and the second
179 list contains distributed disk logs.
180 alog(Log, Term) -> notify_ret()
182 balog(Log, Bytes) -> notify_ret()
184 Types:
186 Log = log()
188 Term = term()
189 Bytes = iodata()
190 notify_ret() = ok | {error, no_such_log}
191 Asynchronously append an item to a disk log. alog/2 is used for
193 internally formatted logs and balog/2 for externally formatted
194 logs. balog/2 can also be used for internally formatted logs if
195 the binary is constructed with a call to term_to_binary/1.
196 Owners subscribing to notifications receive message read_only,
198 blocked_log, or format_external if the item cannot be written on
199 the log, and possibly one of the messages wrap, full, or
200 error_status if an item is written on the log. Message
201 error_status is sent if something is wrong with the header func‐
202 tion or if a file error occurs.
203 alog_terms(Log, TermList) -> notify_ret()
205 balog_terms(Log, ByteList) -> notify_ret()
207 Types:
209 Log = log()
211 TermList = [term()]
212 ByteList = [iodata()]
213 notify_ret() = ok | {error, no_such_log}
214 Asynchronously append a list of items to a disk log.
216 alog_terms/2 is used for internally formatted logs and
217 balog_terms/2 for externally formatted logs. balog_terms/2 can
218 also be used for internally formatted logs if the binaries are
219 constructed with calls to term_to_binary/1.
220 Owners subscribing to notifications receive message read_only,
222 blocked_log, or format_external if the items cannot be written
223 on the log, and possibly one or more of the messages wrap, full,
224 and error_status if items are written on the log. Message
225 error_status is sent if something is wrong with the header func‐
226 tion or if a file error occurs.
227 block(Log) -> ok | {error, block_error_rsn()}
229 block(Log, QueueLogRecords) -> ok | {error, block_error_rsn()}
231 Types:
233 Log = log()
235 QueueLogRecords = boolean()
236 block_error_rsn() = no_such_log | nonode | {blocked_log, log()}
237 With a call to block/1,2 a process can block a log. If the
239 blocking process is not an owner of the log, a temporary link is
240 created between the disk log process and the blocking process.
241 The link ensures that the disk log is unblocked if the blocking
242 process terminates without first closing or unblocking the log.
243 Any process can probe a blocked log with info/1 or close it with
245 close/1. The blocking process can also use functions chunk/2,3,
246 bchunk/2,3, chunk_step/3, and unblock/1 without being affected
247 by the block. Any other attempt than those mentioned so far to
248 update or read a blocked log suspends the calling process until
249 the log is unblocked or returns error message {blocked_log,
250 Log}, depending on whether the value of QueueLogRecords is true
251 or false. QueueLogRecords defaults to true, which is used by
252 block/1.
253 change_header(Log, Header) -> ok | {error, Reason}
255 Types:
257 Log = log()
259 Header =
260 {head, dlog_head_opt()} |
261 {head_func, MFA :: {atom(), atom(), list()}}
262 Reason =
263 no_such_log | nonode |
264 {read_only_mode, Log} |
265 {blocked_log, Log} |
266 {badarg, head}
267 Changes the value of option head or head_func for an owner of a
269 disk log.
270 change_notify(Log, Owner, Notify) -> ok | {error, Reason}
272 Types:
274 Log = log()
276 Owner = pid()
277 Notify = boolean()
278 Reason =
279 no_such_log | nonode |
280 {blocked_log, Log} |
281 {badarg, notify} |
282 {not_owner, Owner}
283 Changes the value of option notify for an owner of a disk log.
285 change_size(Log, Size) -> ok | {error, Reason}
287 Types:
289 Log = log()
291 Size = dlog_size()
292 Reason =
293 no_such_log | nonode |
294 {read_only_mode, Log} |
295 {blocked_log, Log} |
296 {new_size_too_small, Log, CurrentSize :: integer() >= 1}
297 |
298 {badarg, size} |
299 {file_error, file:filename(), file_error()}
300 Changes the size of an open log. For a halt log, the size can
302 always be increased, but it cannot be decreased to something
303 less than the current file size.
304 For a wrap log, both the size and the number of files can always
306 be increased, as long as the number of files does not exceed
307 65000. If the maximum number of files is decreased, the change
308 is not valid until the current file is full and the log wraps to
309 the next file. The redundant files are removed the next time the
310 log wraps around, that is, starts to log to file number 1.
311 As an example, assume that the old maximum number of files is 10
313 and that the new maximum number of files is 6. If the current
314 file number is not greater than the new maximum number of files,
315 files 7-10 are removed when file 6 is full and the log starts to
316 write to file number 1 again. Otherwise, the files greater than
317 the current file are removed when the current file is full (for
318 example, if the current file is 8, files 9 and 10 are removed).
319 The files between the new maximum number of files and the cur‐
320 rent file (that is, files 7 and 8) are removed the next time
321 file 6 is full.
322 If the size of the files is decreased, the change immediately
324 affects the current log. It does not change the size of log
325 files already full until the next time they are used.
326 If the log size is decreased, for example, to save space, func‐
328 tion inc_wrap_file/1 can be used to force the log to wrap.
329 chunk(Log, Continuation) -> chunk_ret()
331 chunk(Log, Continuation, N) -> chunk_ret()
333 bchunk(Log, Continuation) -> bchunk_ret()
335 bchunk(Log, Continuation, N) -> bchunk_ret()
337 Types:
339 Log = log()
341 Continuation = start | continuation()
342 N = integer() >= 1 | infinity
343 chunk_ret() =
344 {Continuation2 :: continuation(), Terms :: [term()]} |
345 {Continuation2 :: continuation(),
346 Terms :: [term()],
347 Badbytes :: integer() >= 0} |
348 eof |
349 {error, Reason :: chunk_error_rsn()}
350 bchunk_ret() =
351 {Continuation2 :: continuation(), Binaries :: [binary()]} |
352 {Continuation2 :: continuation(),
353 Binaries :: [binary()],
354 Badbytes :: integer() >= 0} |
355 eof |
356 {error, Reason :: chunk_error_rsn()}
357 chunk_error_rsn() =
358 no_such_log |
359 {format_external, log()} |
360 {blocked_log, log()} |
361 {badarg, continuation} |
362 {not_internal_wrap, log()} |
363 {corrupt_log_file, FileName :: file:filename()} |
364 {file_error, file:filename(), file_error()}
365 Efficiently reads the terms that are appended to an internally
367 formatted log. It minimizes disk I/O by reading 64 kilobyte
368 chunks from the file. Functions bchunk/2,3 return the binaries
369 read from the file, they do not call binary_to_term(). Apart
370 from that, they work just like chunk/2,3.
371 The first time chunk() (or bchunk()) is called, an initial con‐
373 tinuation, the atom start, must be provided. If a disk log
374 process is running on the current node, terms are read from that
375 log. Otherwise, an individual distributed log on some other node
376 is chosen, if such a log exists.
377 When chunk/3 is called, N controls the maximum number of terms
379 that are read from the log in each chunk. Defaults to infinity,
380 which means that all the terms contained in the 64 kilobyte
381 chunk are read. If less than N terms are returned, this does not
382 necessarily mean that the end of the file is reached.
383 chunk() returns a tuple {Continuation2, Terms}, where Terms is a
385 list of terms found in the log. Continuation2 is yet another
386 continuation, which must be passed on to any subsequent calls to
387 chunk(). With a series of calls to chunk(), all terms from a log
388 can be extracted.
389 chunk() returns a tuple {Continuation2, Terms, Badbytes} if the
391 log is opened in read-only mode and the read chunk is corrupt.
392 Badbytes is the number of bytes in the file found not to be
393 Erlang terms in the chunk. Notice that the log is not repaired.
394 When trying to read chunks from a log opened in read-write mode,
395 tuple {corrupt_log_file, FileName} is returned if the read chunk
396 is corrupt.
397 chunk() returns eof when the end of the log is reached, or
399 {error, Reason} if an error occurs. If a wrap log file is miss‐
400 ing, a message is output on the error log.
401 When chunk/2,3 is used with wrap logs, the returned continuation
403 might not be valid in the next call to chunk(). This is because
404 the log can wrap and delete the file into which the continuation
405 points. To prevent this, the log can be blocked during the
406 search.
407 chunk_info(Continuation) -> InfoList | {error, Reason}
409 Types:
411 Continuation = continuation()
413 InfoList = [{node, Node :: node()}, ...]
414 Reason = {no_continuation, Continuation}
415 Returns the pair {node, Node}, describing the chunk continuation
417 returned by chunk/2,3, bchunk/2,3, or chunk_step/3.
418 Terms are read from the disk log running on Node.
420 chunk_step(Log, Continuation, Step) ->
422 {ok, any()} | {error, Reason}
423 Types:
425 Log = log()
427 Continuation = start | continuation()
428 Step = integer()
429 Reason =
430 no_such_log | end_of_log |
431 {format_external, Log} |
432 {blocked_log, Log} |
433 {badarg, continuation} |
434 {file_error, file:filename(), file_error()}
435 Can be used with chunk/2,3 and bchunk/2,3 to search through an
437 internally formatted wrap log. It takes as argument a continua‐
438 tion as returned by chunk/2,3, bchunk/2,3, or chunk_step/3, and
439 steps forward (or backward) Step files in the wrap log. The con‐
440 tinuation returned, points to the first log item in the new cur‐
441 rent file.
442 If atom start is specified as continuation, a disk log to read
444 terms from is chosen. A local or distributed disk log on the
445 current node is preferred to an individual distributed log on
446 some other node.
447 If the wrap log is not full because all files are not yet used,
449 {error, end_of_log} is returned if trying to step outside the
450 log.
451 close(Log) -> ok | {error, close_error_rsn()}
453 Types:
455 Log = log()
457 close_error_rsn() =
458 no_such_log | nonode |
459 {file_error, file:filename(), file_error()}
460 Closes a local or distributed disk log properly. An internally
462 formatted log must be closed before the Erlang system is
463 stopped. Otherwise, the log is regarded as unclosed and the
464 automatic repair procedure is activated next time the log is
465 opened.
466 The disk log process is not terminated as long as there are own‐
468 ers or users of the log. All owners must close the log, possibly
469 by terminating. Also, any other process, not only the processes
470 that have opened the log anonymously, can decrement the users
471 counter by closing the log. Attempts to close a log by a process
472 that is not an owner are ignored if there are no users.
473 If the log is blocked by the closing process, the log is also
475 unblocked.
476 format_error(Error) -> io_lib:chars()
478 Types:
480 Error = term()
482 Given the error returned by any function in this module, this
484 function returns a descriptive string of the error in English.
485 For file errors, function format_error/1 in module file is
486 called.
487 inc_wrap_file(Log) -> ok | {error, inc_wrap_error_rsn()}
489 Types:
491 Log = log()
493 inc_wrap_error_rsn() =
494 no_such_log | nonode |
495 {read_only_mode, log()} |
496 {blocked_log, log()} |
497 {halt_log, log()} |
498 {invalid_header, invalid_header()} |
499 {file_error, file:filename(), file_error()}
500 invalid_header() = term()
501 Forces the internally formatted disk log to start logging to the
503 next log file. It can be used, for example, with change_size/2
504 to reduce the amount of disk space allocated by the disk log.
505 Owners subscribing to notifications normally receive a wrap mes‐
507 sage, but if an error occurs with a reason tag of invalid_header
508 or file_error, an error_status message is sent.
509 info(Log) -> InfoList | {error, no_such_log}
511 Types:
513 Log = log()
515 InfoList = [dlog_info()]
516 dlog_info() =
517 {name, Log :: log()} |
518 {file, File :: file:filename()} |
519 {type, Type :: dlog_type()} |
520 {format, Format :: dlog_format()} |
521 {size, Size :: dlog_size()} |
522 {mode, Mode :: dlog_mode()} |
523 {owners, [{pid(), Notify :: boolean()}]} |
524 {users, Users :: integer() >= 0} |
525 {status,
526 Status :: ok | {blocked, QueueLogRecords :: boolean()}} |
527 {node, Node :: node()} |
528 {distributed, Dist :: local | [node()]} |
529 {head,
530 Head ::
531 none | {head, term()} | (MFA :: {atom(), atom(), list()})} |
532 {no_written_items, NoWrittenItems :: integer() >= 0} |
533 {full, Full :: boolean} |
534 {no_current_bytes, integer() >= 0} |
535 {no_current_items, integer() >= 0} |
536 {no_items, integer() >= 0} |
537 {current_file, integer() >= 1} |
538 {no_overflows,
539 {SinceLogWasOpened :: integer() >= 0,
540 SinceLastInfo :: integer() >= 0}}
541 Returns a list of {Tag, Value} pairs describing the log. If a
543 disk log process is running on the current node, that log is
544 used as source of information, otherwise an individual distrib‐
545 uted log on some other node is chosen, if such a log exists.
546 The following pairs are returned for all logs:
548 {name, Log}:
550 Log is the log name as specified by the open/1 option name.
551 {file, File}:
553 For halt logs File is the filename, and for wrap logs File
554 is the base name.
555 {type, Type}:
557 Type is the log type as specified by the open/1 option type.
558 {format, Format}:
560 Format is the log format as specified by the open/1 option
561 format.
562 {size, Size}:
564 Size is the log size as specified by the open/1 option size,
565 or the size set by change_size/2. The value set by
566 change_size/2 is reflected immediately.
567 {mode, Mode}:
569 Mode is the log mode as specified by the open/1 option mode.
570 {owners, [{pid(), Notify}]}:
572 Notify is the value set by the open/1 option notify or func‐
573 tion change_notify/3 for the owners of the log.
574 {users, Users}:
576 Users is the number of anonymous users of the log, see the
577 open/1 option linkto.
578 {status, Status}:
580 Status is ok or {blocked, QueueLogRecords} as set by func‐
581 tions block/1,2 and unblock/1.
582 {node, Node}:
584 The information returned by the current invocation of func‐
585 tion info/1 is gathered from the disk log process running on
586 Node.
587 {distributed, Dist}:
589 If the log is local on the current node, Dist has the value
590 local, otherwise all nodes where the log is distributed are
591 returned as a list.
592 The following pairs are returned for all logs opened in
594 read_write mode:
595 {head, Head}:
597 Depending on the value of the open/1 options head and
598 head_func, or set by function change_header/2, the value of
599 Head is none (default), {head, H} (head option), or {M,F,A}
600 (head_func option).
601 {no_written_items, NoWrittenItems}:
603 NoWrittenItems is the number of items written to the log
604 since the disk log process was created.
605 The following pair is returned for halt logs opened in
607 read_write mode:
608 {full, Full}:
610 Full is true or false depending on whether the halt log is
611 full or not.
612 The following pairs are returned for wrap logs opened in
614 read_write mode:
615 {no_current_bytes, integer() >= 0}:
617 The number of bytes written to the current wrap log file.
618 {no_current_items, integer() >= 0}:
620 The number of items written to the current wrap log file,
621 header inclusive.
622 {no_items, integer() >= 0}:
624 The total number of items in all wrap log files.
625 {current_file, integer()}:
627 The ordinal for the current wrap log file in the range
628 1..MaxNoFiles, where MaxNoFiles is specified by the open/1
629 option size or set by change_size/2.
630 {no_overflows, {SinceLogWasOpened, SinceLastInfo}}:
632 SinceLogWasOpened (SinceLastInfo) is the number of times a
633 wrap log file has been filled up and a new one is opened or
634 inc_wrap_file/1 has been called since the disk log was last
635 opened (info/1 was last called). The first time info/2 is
636 called after a log was (re)opened or truncated, the two val‐
637 ues are equal.
638 Notice that functions chunk/2,3, bchunk/2,3, and chunk_step/3 do
640 not affect any value returned by info/1.
641 lclose(Log) -> ok | {error, lclose_error_rsn()}
643 lclose(Log, Node) -> ok | {error, lclose_error_rsn()}
645 Types:
647 Log = log()
649 Node = node()
650 lclose_error_rsn() =
651 no_such_log | {file_error, file:filename(), file_error()}
652 lclose/1 closes a local log or an individual distributed log on
654 the current node.
655 lclose/2 closes an individual distributed log on the specified
657 node if the node is not the current one.
658 lclose(Log) is equivalent to lclose(Log, node()). See also
660 close/1.
661 If no log with the specified name exist on the specified node,
663 no_such_log is returned.
664 log(Log, Term) -> ok | {error, Reason :: log_error_rsn()}
666 blog(Log, Bytes) -> ok | {error, Reason :: log_error_rsn()}
668 Types:
670 Log = log()
672 Term = term()
673 Bytes = iodata()
674 log_error_rsn() =
675 no_such_log | nonode |
676 {read_only_mode, log()} |
677 {format_external, log()} |
678 {blocked_log, log()} |
679 {full, log()} |
680 {invalid_header, invalid_header()} |
681 {file_error, file:filename(), file_error()}
682 Synchronously appends a term to a disk log. Returns ok or
684 {error, Reason} when the term is written to disk. If the log is
685 distributed, ok is returned, unless all nodes are down. Terms
686 are written by the ordinary write() function of the operating
687 system. Hence, it is not guaranteed that the term is written to
688 disk, it can linger in the operating system kernel for a while.
689 To ensure that the item is written to disk, function sync/1 must
690 be called.
691 log/2 is used for internally formatted logs, and blog/2 for
693 externally formatted logs. blog/2 can also be used for inter‐
694 nally formatted logs if the binary is constructed with a call to
695 term_to_binary/1.
696 Owners subscribing to notifications are notified of an error
698 with an error_status message if the error reason tag is
699 invalid_header or file_error.
700 log_terms(Log, TermList) ->
702 ok | {error, Resaon :: log_error_rsn()}
703 blog_terms(Log, BytesList) ->
705 ok | {error, Reason :: log_error_rsn()}
706 Types:
708 Log = log()
710 TermList = [term()]
711 BytesList = [iodata()]
712 log_error_rsn() =
713 no_such_log | nonode |
714 {read_only_mode, log()} |
715 {format_external, log()} |
716 {blocked_log, log()} |
717 {full, log()} |
718 {invalid_header, invalid_header()} |
719 {file_error, file:filename(), file_error()}
720 Synchronously appends a list of items to the log. It is more
722 efficient to use these functions instead of functions log/2 and
723 blog/2. The specified list is split into as large sublists as
724 possible (limited by the size of wrap log files), and each sub‐
725 list is logged as one single item, which reduces the overhead.
726 log_terms/2 is used for internally formatted logs, and
728 blog_terms/2 for externally formatted logs. blog_terms/2 can
729 also be used for internally formatted logs if the binaries are
730 constructed with calls to term_to_binary/1.
731 Owners subscribing to notifications are notified of an error
733 with an error_status message if the error reason tag is
734 invalid_header or file_error.
735 open(ArgL) -> open_ret() | dist_open_ret()
737 Types:
739 ArgL = dlog_options()
741 dlog_options() = [dlog_option()]
742 dlog_option() =
743 {name, Log :: log()} |
744 {file, FileName :: file:filename()} |
745 {linkto, LinkTo :: none | pid()} |
746 {repair, Repair :: true | false | truncate} |
747 {type, Type :: dlog_type()} |
748 {format, Format :: dlog_format()} |
749 {size, Size :: dlog_size()} |
750 {distributed, Nodes :: [node()]} |
751 {notify, boolean()} |
752 {head, Head :: dlog_head_opt()} |
753 {head_func, MFA :: {atom(), atom(), list()}} |
754 {quiet, boolean()} |
755 {mode, Mode :: dlog_mode()}
756 open_ret() = ret() | {error, open_error_rsn()}
757 ret() =
758 {ok, Log :: log()} |
759 {repaired,
760 Log :: log(),
761 {recovered, Rec :: integer() >= 0},
762 {badbytes, Bad :: integer() >= 0}}
763 dist_open_ret() =
764 {[{node(), ret()}], [{node(), {error, dist_error_rsn()}}]}
765 dist_error_rsn() = nodedown | open_error_rsn()
766 open_error_rsn() =
767 no_such_log |
768 {badarg, term()} |
769 {size_mismatch,
770 CurrentSize :: dlog_size(),
771 NewSize :: dlog_size()} |
772 {arg_mismatch,
773 OptionName :: dlog_optattr(),
774 CurrentValue :: term(),
775 Value :: term()} |
776 {name_already_open, Log :: log()} |
777 {open_read_write, Log :: log()} |
778 {open_read_only, Log :: log()} |
779 {need_repair, Log :: log()} |
780 {not_a_log_file, FileName :: file:filename()} |
781 {invalid_index_file, FileName :: file:filename()} |
782 {invalid_header, invalid_header()} |
783 {file_error, file:filename(), file_error()} |
784 {node_already_open, Log :: log()}
785 dlog_optattr() =
786 name | file | linkto | repair | type | format | size |
787 distributed | notify | head | head_func | mode
788 dlog_size() =
789 infinity |
790 integer() >= 1 |
791 {MaxNoBytes :: integer() >= 1, MaxNoFiles :: integer() >= 1}
792 Parameter ArgL is a list of the following options:
794 {name, Log}:
796 Specifies the log name. This name must be passed on as a
797 parameter in all subsequent logging operations. A name must
798 always be supplied.
799 {file, FileName}:
801 Specifies the name of the file to be used for logged terms.
802 If this value is omitted and the log name is an atom or a
803 string, the filename defaults to lists:concat([Log, ".LOG"])
804 for halt logs.
805 For wrap logs, this is the base name of the files. Each file
807 in a wrap log is called <base_name>.N, where N is an inte‐
808 ger. Each wrap log also has two files called <base_name>.idx
809 and <base_name>.siz.
810 {linkto, LinkTo}:
812 If LinkTo is a pid, it becomes an owner of the log. If
813 LinkTo is none, the log records that it is used anonymously
814 by some process by incrementing the users counter. By
815 default, the process that calls open/1 owns the log.
816 {repair, Repair}:
818 If Repair is true, the current log file is repaired, if
819 needed. As the restoration is initiated, a message is output
820 on the error log. If false is specified, no automatic repair
821 is attempted. Instead, the tuple {error, {need_repair, Log}}
822 is returned if an attempt is made to open a corrupt log
823 file. If truncate is specified, the log file becomes trun‐
824 cated, creating an empty log. Defaults to true, which has no
825 effect on logs opened in read-only mode.
826 {type, Type}:
828 The log type. Defaults to halt.
829 {format, Format}:
831 Disk log format. Defaults to internal.
832 {size, Size}:
834 Log size.
835 When a halt log has reached its maximum size, all attempts
837 to log more items are rejected. Defaults to infinity, which
838 for halt implies that there is no maximum size.
839 For wrap logs, parameter Size can be a pair {MaxNoBytes,
841 MaxNoFiles} or infinity. In the latter case, if the files of
842 an existing wrap log with the same name can be found, the
843 size is read from the existing wrap log, otherwise an error
844 is returned.
845 Wrap logs write at most MaxNoBytes bytes on each file and
847 use MaxNoFiles files before starting all over with the first
848 wrap log file. Regardless of MaxNoBytes, at least the header
849 (if there is one) and one item are written on each wrap log
850 file before wrapping to the next file.
851 When opening an existing wrap log, it is not necessary to
853 supply a value for option Size, but any supplied value must
854 equal the current log size, otherwise the tuple {error,
855 {size_mismatch, CurrentSize, NewSize}} is returned.
856 {distributed, Nodes}:
858 This option can be used for adding members to a distributed
859 disk log. Defaults to [], which means that the log is local
860 on the current node.
861 {notify, boolean()}:
863 If true, the log owners are notified when certain log events
864 occur. Defaults to false. The owners are sent one of the
865 following messages when an event occurs:
866 {disk_log, Node, Log, {wrap, NoLostItems}}:
868 Sent when a wrap log has filled up one of its files and a
869 new file is opened. NoLostItems is the number of previ‐
870 ously logged items that were lost when truncating existing
871 files.
872 {disk_log, Node, Log, {truncated, NoLostItems}}:
874 Sent when a log is truncated or reopened. For halt logs
875 NoLostItems is the number of items written on the log
876 since the disk log process was created. For wrap logs
877 NoLostItems is the number of items on all wrap log files.
878 {disk_log, Node, Log, {read_only, Items}}:
880 Sent when an asynchronous log attempt is made to a log
881 file opened in read-only mode. Items is the items from the
882 log attempt.
883 {disk_log, Node, Log, {blocked_log, Items}}:
885 Sent when an asynchronous log attempt is made to a blocked
886 log that does not queue log attempts. Items is the items
887 from the log attempt.
888 {disk_log, Node, Log, {format_external, Items}}:
890 Sent when function alog/2 or alog_terms/2 is used for
891 internally formatted logs. Items is the items from the log
892 attempt.
893 {disk_log, Node, Log, full}:
895 Sent when an attempt to log items to a wrap log would
896 write more bytes than the limit set by option size.
897 {disk_log, Node, Log, {error_status, Status}}:
899 Sent when the error status changes. The error status is
900 defined by the outcome of the last attempt to log items to
901 the log, or to truncate the log, or the last use of func‐
902 tion sync/1, inc_wrap_file/1, or change_size/2. Status is
903 either ok or {error, Error}, the former is the initial
904 value.
905 {head, Head}:
907 Specifies a header to be written first on the log file. If
908 the log is a wrap log, the item Head is written first in
909 each new file. Head is to be a term if the format is inter‐
910 nal, otherwise a sequence of bytes. Defaults to none, which
911 means that no header is written first on the file.
912 {head_func, {M,F,A}}:
914 Specifies a function to be called each time a new log file
915 is opened. The call M:F(A) is assumed to return {ok, Head}.
916 The item Head is written first in each file. Head is to be a
917 term if the format is internal, otherwise a sequence of
918 bytes.
919 {mode, Mode}:
921 Specifies if the log is to be opened in read-only or read-
922 write mode. Defaults to read_write.
923 {quiet, Boolean}:
925 Specifies if messages will be sent to error_logger on recov‐
926 erable errors with the log files. Defaults to false.
927 open/1 returns {ok, Log} if the log file is successfully opened.
929 If the file is successfully repaired, the tuple {repaired, Log,
930 {recovered, Rec}, {badbytes, Bad}} is returned, where Rec is the
931 number of whole Erlang terms found in the file and Bad is the
932 number of bytes in the file that are non-Erlang terms. If the
933 parameter distributed is specified, open/1 returns a list of
934 successful replies and a list of erroneous replies. Each reply
935 is tagged with the node name.
936 When a disk log is opened in read-write mode, any existing log
938 file is checked for. If there is none, a new empty log is cre‐
939 ated, otherwise the existing file is opened at the position
940 after the last logged item, and the logging of items starts from
941 there. If the format is internal and the existing file is not
942 recognized as an internally formatted log, a tuple {error,
943 {not_a_log_file, FileName}} is returned.
944 open/1 cannot be used for changing the values of options of an
946 open log. When there are prior owners or users of a log, all
947 option values except name, linkto, and notify are only checked
948 against the values supplied before as option values to function
949 open/1, change_header/2, change_notify/3, or change_size/2.
950 Thus, none of the options except name is mandatory. If some
951 specified value differs from the current value, a tuple {error,
952 {arg_mismatch, OptionName, CurrentValue, Value}} is returned.
953 Note:
955 If an owner attempts to open a log as owner once again, it is
956 acknowledged with the return value {ok, Log}, but the state of
957 the disk log is not affected.
958 If a log with a specified name is local on some node, and one
961 tries to open the log distributed on the same node, the tuple
962 {error, {node_already_open, Log}} is returned. The same tuple is
963 returned if the log is distributed on some node, and one tries
964 to open the log locally on the same node. Opening individual
965 distributed disk logs for the first time adds those logs to a
966 (possibly empty) distributed disk log. The supplied option val‐
967 ues are used on all nodes mentioned by option distributed. Indi‐
968 vidual distributed logs know nothing about each other's option
969 values, so each node can be given unique option values by creat‐
970 ing a distributed log with many calls to open/1.
971 A log file can be opened more than once by giving different val‐
973 ues to option name or by using the same file when distributing a
974 log on different nodes. It is up to the user of module disk_log
975 to ensure that not more than one disk log process has write
976 access to any file, otherwise the file can be corrupted.
977 If an attempt to open a log file for the first time fails, the
979 disk log process terminates with the EXIT message {{failed,Rea‐
980 son},[{disk_log,open,1}]}. The function returns {error, Reason}
981 for all other errors.
982 pid2name(Pid) -> {ok, Log} | undefined
984 Types:
986 Pid = pid()
988 Log = log()
989 Returns the log name given the pid of a disk log process on the
991 current node, or undefined if the specified pid is not a disk
992 log process.
993 This function is meant to be used for debugging only.
995 reopen(Log, File) -> ok | {error, reopen_error_rsn()}
997 reopen(Log, File, Head) -> ok | {error, reopen_error_rsn()}
999 breopen(Log, File, BHead) -> ok | {error, reopen_error_rsn()}
1001 Types:
1003 Log = log()
1005 File = file:filename()
1006 Head = term()
1007 BHead = iodata()
1008 reopen_error_rsn() =
1009 no_such_log | nonode |
1010 {read_only_mode, log()} |
1011 {blocked_log, log()} |
1012 {same_file_name, log()} |
1013 {invalid_index_file, file:filename()} |
1014 {invalid_header, invalid_header()} |
1015 {file_error, file:filename(), file_error()}
1016 Renames the log file to File and then recreates a new log file.
1018 If a wrap log exists, File is used as the base name of the
1019 renamed files. By default the header given to open/1 is written
1020 first in the newly opened log file, but if argument Head or
1021 BHead is specified, this item is used instead. The header argu‐
1022 ment is used only once. Next time a wrap log file is opened, the
1023 header given to open/1 is used.
1024 reopen/2,3 are used for internally formatted logs, and breopen/3
1026 for externally formatted logs.
1027 Owners subscribing to notifications receive a truncate message.
1029 Upon failure to reopen the log, the disk log process terminates
1031 with the EXIT message {{failed,Error},[{disk_log,Fun,Arity}]}.
1032 Other processes having requests queued receive the message
1033 {disk_log, Node, {error, disk_log_stopped}}.
1034 sync(Log) -> ok | {error, sync_error_rsn()}
1036 Types:
1038 Log = log()
1040 sync_error_rsn() =
1041 no_such_log | nonode |
1042 {read_only_mode, log()} |
1043 {blocked_log, log()} |
1044 {file_error, file:filename(), file_error()}
1045 Ensures that the contents of the log are written to the disk.
1047 This is usually a rather expensive operation.
1048 truncate(Log) -> ok | {error, trunc_error_rsn()}
1050 truncate(Log, Head) -> ok | {error, trunc_error_rsn()}
1052 btruncate(Log, BHead) -> ok | {error, trunc_error_rsn()}
1054 Types:
1056 Log = log()
1058 Head = term()
1059 BHead = iodata()
1060 trunc_error_rsn() =
1061 no_such_log | nonode |
1062 {read_only_mode, log()} |
1063 {blocked_log, log()} |
1064 {invalid_header, invalid_header()} |
1065 {file_error, file:filename(), file_error()}
1066 Removes all items from a disk log. If argument Head or BHead is
1068 specified, this item is written first in the newly truncated
1069 log, otherwise the header given to open/1 is used. The header
1070 argument is used only once. Next time a wrap log file is opened,
1071 the header given to open/1 is used.
1072 truncate/1,2 are used for internally formatted logs, and btrun‐
1074 cate/2 for externally formatted logs.
1075 Owners subscribing to notifications receive a truncate message.
1077 If the attempt to truncate the log fails, the disk log process
1079 terminates with the EXIT message {{failed,Rea‐
1080 son},[{disk_log,Fun,Arity}]}. Other processes having requests
1081 queued receive the message {disk_log, Node, {error,
1082 disk_log_stopped}}.
1083 unblock(Log) -> ok | {error, unblock_error_rsn()}
1085 Types:
1087 Log = log()
1089 unblock_error_rsn() =
1090 no_such_log | nonode |
1091 {not_blocked, log()} |
1092 {not_blocked_by_pid, log()}
1093 Unblocks a log. A log can only be unblocked by the blocking
1095 process.
1096
1098 file(3), pg2(3), wrap_log_reader(3)
1099Ericsson AB kernel 6.5.2 disk_log(3)