small complexity reduction, renaming variables, change ordering, remove braindead...

[rersyncrecent.git] / Todo

2008-09-27  Andreas J. Koenig  <andreas.koenig.7os6VVqR@franz.ak.mind.de>

        * Todo: find all todos together and make a plan what is missing for a
        release.

        - verifytree or something like that. fsck maybe.

        - rersyncrecent, the script itself

        - a way to only mirror the recentfiles without mirroring the whole
        remote system such that people can decide to mirror only partially see
        also 2008-08-30
        
        - long living objects that mirror again and again. Inject something
        into ta, see how it goes over to tb.

        - how do we continue filling up the DONE system when we use an object
        for the second time? "fully covered" and "uptodate" or new terminology.

        - idea: have a new flag on recentfiles with the meaning: if this
        changes, you're required to run a full rsync over all the files. The
        reason why we set it would probably be: some foul happened. we injected
        files in arbitrary places or didn't inject them although they changed.
        The content of the flag? Timestamp? The relation between the
        recentfiles would have to be inheritance from the principal, because any
        out of band changes would soon later propagate to the next recentfile.

        By upping the flag often one can easily ruin the slaves.

        last out of band change? dirtymark?

        Anyway, this implies that we read a potentially existing recentfile
        before we write one.

        And it implies that we have an eventloop that keeps us busy in 2-3
        cycles, one for current stuff (tight loop) and one for the recentfiles
        (cascade when principal has changed), one for the old stuff after a
        dirtymark change.

        - overview called on the wrong file should be understandable

        - See that the long running process really only updates the principal
        file unless it has missed a timespan during which something happened. If
        nothing happened, it must notice even when it misses the timespan.

        - fill up recentfiles with fake (historic) entries; fill up with
        individual corrections; algorithm maybe to be done with bigfloat so that
        we can always place something in the middle between two entries

        - the meta data field that must change when we fake something up so that
        the downstream people know they have to re-fetch everything.

        - how tolerant are we against missing files upstream? how do we keep
        track? there are legitimate cases where we did read upstream index right
        before a file got deleted there and then find that file as new and want
        it. There are other cases that are not self healing and must be tracked
        and bugreported.

        - how, exactly, do we have to deal with deletes? With rsync errors? 

        rsync: link_stat "/id/K/KA/KARMAN/Rose-HTMLx-Form-Related-0.07.meta" (in
        authors) failed: No such file or directory (2)

        The file above is a delete in 1h and a new in file 1M and the
        delete in the locally running rmirror did not get propagated to the 1M
        object. Bug. And the consequence is a standstill.

        It seems that a slave that works with a file below the principal needs
        to merge things all the way up to get rid of later deletes. Or keep
        track of all deletes and skip them later. So we need a trackdeletes.pm
        similar to the done.pm?

        see also 2008-08-20 about spurious deletes that really have no add
        counterpart and yet they are not wrong.

        - consider the effect when resyncing the recentfile takes longer than
        the time per loop. Then we never rsync any file. We need to diagnose
        that and force an increase of that loop time. But when we later are fast
        enough again because the net has recovered, then we need to switch back
        to original parameters.

        - remember to verify that no temp files are left lying around and the
        signal handler

        - we must throw away the pathdb when wee have reached the end of Z. From
        that moment we can have a very small pathdb because the only reason for
        a pathdb is that we know to ignore old records in old files. We won't
        need this pathdb again before the next full pass over the data is
        necessary and then we will rebuild it as we go along.

        - status file for not long running jobs that want to track upstream with
        a, say, cronjob.

        - revisit all XXX _float areas and study Sub::Exporter

        - persistent DB even though we just said we do not need it. Just for
        extended capabilities and time savings when, for example, upstream
        announces a reset and we get new recentfiles and could then limit
        ourselves to a subset of files (those that have a changed epoch) in a
        first pass and would only then do the llop to verify the rest. Or
        something.

        - lookup by epoch and by path and use this ability on the pause to never
        again register a file twice that doesn't need it.
        
        * Todo: aggregate files should know their feed and finding the principal
        should be done stepwise. (?)

        * Todo: DESTROY thing that unlocks. Today when I left the debuggerr I
        left locks around. DONE

2008-09-26  Andreas J. Koenig  <andreas.koenig.7os6VVqR@franz.ak.mind.de>

        * maybe extend the _overview so that it always says if and where the
        last file is in the next file and where the next event in the next rf
        would lie. No, don't like this anymore. REJECT

        * take the two new redundant tests out again, only the third must
        survive. DONE

        * Todo: add a sanity check if the merged structure is really pointing to
        a different rf and that this different rf is larger. DONE

2008-09-25  Andreas J. Koenig  <andreas.koenig.7os6VVqR@franz.ak.mind.de>

        * now test, if they are overlapping. And test if there is a file in the
        next rf that would fit into this rf's interval.

        1h  1222324012.8474  1222322541.7963           0.4086
        6h  1222320411.2760  1222304207.6931           4.5010 missing overlap/gap!
        1d  1222320411.2760  1222238750.5071          22.6835 large overlap
        1W  1222313218.3626  1221708477.5829         167.9835

        I suspect that somebody writes a merged timestamp without having merged
        and then somebody else relies on it.

        If aggregate is running, the intervals must not be extravagated, if it
        is not running, there must not be bounds, the total number of events in
        the system must be counted and must be controlled throughout the tests.
        That the test required the additional update was probably nonsense,
        because aggregate can cut pieces too. FIXED & DONE

2008-09-23  Andreas J. Koenig  <andreas.koenig.7os6VVqR@franz.ak.mind.de>

        * rrr-aggregate seems to rewrite the RECENT file even if nothing has
        changed. FIXED

2008-09-21  Andreas J. Koenig  <andreas.koenig.7os6VVqR@franz.ak.mind.de>

        * Most apparent bug at the moment is that the recentfiles are fetched
        too often. Only the principal should be fetched and if it has not
        changed, the others should not be refetched. ATM I must admit that I'm
        happy that we refetch more often than needed because I can more easily
        fix bugs while the thing is running.

        * Let's say, 1220474966.19501 is a timestamp of a file that is already
        done but the done system does not know about it. The reason for the
        failure is not known and we never reach the status uptodate because of
        this. We must get over it.

        Later it turns out that the origin server had a bug somewhere.
        1220474966.19042 came after 1220474966.19501. Or better: it was in the
        array of the recentfile one position above. The bug was my own.

2008-09-20  Andreas J. Koenig  <andreas.koenig.7os6VVqR@franz.ak.mind.de>

        * There is the race condition where the server does a delete and the
        slave does not yet know and then tries to download it because he sees
        the new. So for this time window we must be more tolerant against
        failure. If we cannot download a file, we should just skip it and should
        not retry immediately. The whole system should discover the lost thing
        later. Keeping track with the DONE system should really be a no brainer.

        But there is something more: the whole filesystem is a database and the
        recentfiles are one possible representation of it. It's a pretty useful
        representation I think that's why I have implemented something around
        it. But for strictly local operation it has little value. For local
        operation we would much rather have a database. So we would enter every
        recentfile reading and every rsync operation and for every file the last
        state change and what it leads to. Then we would always ignore older
        records without the efforts involved with recentfiles.

        The database would have: path,recentepoch,rsyncedon,deletedon

        Oh well, not yet clear where this leads to.

2008-09-19  Andreas J. Koenig  <andreas.koenig.7os6VVqR@franz.ak.mind.de>

        * Bug: the bigloop ran into a funny endless loop after EWILHELM uploaded
        Module-Build. It *only* rsynced the "1h" recentfile from that moment on.

        * statusfile, maybe only on demand, alone to have a sharp debugging
        tool. It is locked and all recentfiles dump themselves into it and we
        can build a viewer that lets us know where we stand and what's inside.

        * remember: only the principal recentfile needs expiration, all others
        shall be expired by principal if it discovers that something has move
        upstream.

2008-09-18  Andreas J. Koenig  <andreas.koenig.7os6VVqR@franz.ak.mind.de>

        * Always check if we stringify to a higher value than in the entry
        before. DONE

        * And in covered make an additional check if we would be able to see a
        numerical difference between the two numbers and if we can't then switch
        to a different, more expensive algorithm. Do not want to be caught by
        floating surprises. DONE

2008-09-17  Andreas J. Koenig  <andreas.koenig.7os6VVqR@franz.ak.mind.de>

        * caching has several aspects here: we can cache the interval of the
        recentfile which only will change when the mtime of the file changes. We
        must re-mirror the recentfile when its ttl has expired. Does have_read
        tell you anything? It counts nothing at all. Only the mtime is
        interesting. The ntuple mtime, low-epoch, high-epoch. And as a separate
        thing the have_mirrored because it is unrelated to the mtime.

        * Robustness of floating point calculations! I always thought that the
        string calculated by the origin server for the floating representation
        of the epoch time is just a string. When we convert it to a number and
        later back to a string, the other computer might come to a different
        conclusion. This must not happen, we want to preserve it under any
        circumstances. I will have to write tests with overlong sequences that
        get lost in arithmetic and must see if all still works well. DONE

        But one fragile point remains: if one host considers a>b and the other
        one considers them == but no eq. To prevent this, we must probably do
        some extra homework. DONE

2008-09-16  Andreas J. Koenig  <andreas.koenig.7os6VVqR@franz.ak.mind.de>

        * the concept of tracking DONE needs an object per recentfile that has
        something like these methods:

        do_we_have(xxx), we_have(xxx), do_we_have_all(xxx,yyy), reset()

        covered()        register()    covered()

        The unclear thing is how we translate points in time into intervals. We
        could pass a reference to the current recent_events array when running
        we_have(xxx) and let the DONE object iterate over it such that it only
        has to store a list of intervals that can melt into each other. Ah, even
        passing the list together with a list of indexes seems feasiable.

        Or maybe ask for the inverted list?

        Whenever the complete array is covered by the interval we say we are
        fully covered and if the recentfile is not expired, we are uptodate.

2008-09-07  Andreas J. Koenig  <andreas.koenig.7os6VVqR@franz.ak.mind.de>

2008-09-05  Andreas J. Koenig  <andreas.koenig.7os6VVqR@franz.ak.mind.de>

        * need a way to "return" the next entry after the end of a list. When
        the caller says "before" or "after" we would like to know if he could
        cover that interval/threshold or not because this influences the effect
        of a newer timestamp of that recentfile. DONE with $opt{info}.

2008-09-04  Andreas J. Koenig  <andreas.koenig.7os6VVqR@franz.ak.mind.de>

        * one of the next things to tackle: the equivalent of csync2 -TIXU.

        loop implies tixu (?). Nope, something like --statefile decides. Per
        default we do ...?

        T test, I init, X including removals, U nodirtymark

        So we have no concept of dirtymarks, we only trust that since we are
        running we have observed everything steadily. But people will not let
        this program run forever so we must consider both startup penalty and
        book keeping for later runs. We keep this for later. For now we write a
        long running mirror that merges several intervals.

2008-09-02  Andreas J. Koenig  <andreas.koenig.7os6VVqR@franz.ak.mind.de>

        * need to speed up the 02 test, it's not clever to sleep so much. Reduce
        the intervals!

        * rersyncrecent, the script: default to one week. The name of the switch
        is --after. Other switches? --loop!

2008-08-30  Andreas J. Koenig  <andreas.koenig.7os6VVqR@franz.ak.mind.de>

        * need a switch --skip-deletes (?)

        * need a switch --enduser that tells us that the whole tempfile
        discipline is not needed when there is no downstream user. (?)

        Without this switch we cannot have a reasonable recent.pl that just
        displays the recent additions. Either we accept to download everything.
        Or we download temporary files without the typical rsync protocol
        advantages.

        Or maybe the switch is --tmpdir? If --tmpdir would mean: do not use
        File::Temp::tempdir, this might be a win.

2008-08-29  Andreas J. Koenig  <andreas.koenig.7os6VVqR@franz.ak.mind.de>

        * apropos missing: we have no push, we never know the downstream
        servers. People who know their downstream hosts and want to ascertain
        something will want additional methods we have never thought about, like
        update or delete a certain file.

2008-08-26  Andreas J. Koenig  <andreas.koenig.7os6VVqR@franz.ak.mind.de>

        * tempted to refactor rmirror into resolve_symlink, localize, etc.
        Curious if rsync_options=links equal 0 vs. 1 will make the expected
        difference.

        * rsync options: it's a bit of a pain that we usually need several rsync
        options, like compress, links, times, checksum and that there is no
        reasonable default except the original rsync default. I think wee can
        safely assume that the rsync options are shared between all recentfile
        instances within one recent tree.

2008-08-20  Andreas J. Koenig  <andreas.koenig.7os6VVqR@franz.ak.mind.de>

        * deletes: if a delete follows an add quickly enough it may happen that
        a downstream mirror did not see the add at all! It seems this needs to
        be mentioned somewhere. The point here is that even if the downstream is
        never missing the principal timeframe it may encounter a "delete" that
        has no complimentary "add" anywhere.

2008-08-19  Andreas J. Koenig  <andreas.koenig.7os6VVqR@franz.ak.mind.de>

        * I suspect the treat of metadata is incorrect during read or something.
        The bug that I am watching is that between 06:08 and 06:09 the 6h file
        contained more than 6 hours worth of data. At 06:08 we merged into the
        1d file. We need to take snapshots of the 6h file over the course of an
        hour or maybe only between XX:08 and XX:09? Nope, the latter is not
        enough.

        Much worse: watching the 1h file: right at the moment (at 06:35) it
        covers 1218867584-1219120397 which is 70 hours.

        Something terribly broken. BTW, 1218867584 corresponds to Sat Aug 16
        08:19:44 2008, that is when I checked out last time, so it seems to be
        aggregating and never truncating?

        No, correct is: it is never truncating; but wrong is: it is aggregating.
        It does receive a lot of events from time to time from a larger file.
        Somehow a large file gets merged into the small one and because the
        "meta/merged" attribute is missing, nobody is paying attention. I
        believe that I can fix this by making sure that metadata are honoured
        during read. DONE and test adjusted.

2008-08-17  Andreas J. Koenig  <andreas.koenig.7os6VVqR@franz.ak.mind.de>

        * grand renaming plan

        remotebase          => remoteroot   to fit well with localroot        DONE
        local_path()        => localroot    seems to me should already work   DONE
        recentfile_basename => rfilename    no need to stress it has no slash DONE

        filenameroot??? Doesn't seem too bad to me today. Maybe something like
        kern? It would anyway need a deprecation cycle because it is an
        important constructor.

        * I like the portability that Data::Serializer brings us but the price
        is that some day we might find out that it is slowing us a bit. We'll
        see.

2008-08-16  Andreas J. Koenig  <andreas.koenig.7os6VVqR@franz.ak.mind.de>

        * should we not enter the interval of the principal (or the interval of
        the merging file?) in every aggregated/merged file?

        * we should aim at a first release and give up on thinking about
        sanitizing stuff and zloop. Let's just admit that a full traditional
        rsync is the only available sanitizer ATM. Otherwise it's complicated
        stuff: sanitizing on the origin server, sanitizing on the slaves,
        sanitizing forgotten files, broken timestamps, etc. Let's delay it and
        get the basics out before this becomes a major cause for mess.

2008-08-13  Andreas Koenig  <k@andreas-koenigs-computer.local>

        * On OSes not supporting symlinks we expect that RECENT.recent contains
        the contents of the principal recentfile. Actually this is identical on
        systems supporting symlinks. Simple, what follows from that is that we
        need to keep the serializer in the metadata because we cannot read it
        from the filename, doesn't it? Of course not. It's a chicken and egg
        problem. This leaves us with the problem to actually parse the
        serialized data to find out in which format it is. So who can do the 4
        or 5 magics we wanted to support? File::LibMagic?

2008-08-09  Andreas Koenig  <k@andreas-koenigs-computer.local>

        * remotebase and recentfile_basename are ugly names. Now that we need a
        word for the shortest/principal/driving recentfile too we should do
        something about it.

        localroot is good. rfile is good. local_path() is bad, local_path($path)
        is medium, filenameroot() is bad, remotebase is bad, recentfile is
        already deprecated.

        Up to now remotebase was the string that described the remote root
        directory in rsync notation, like pause.perl.org::authors. And
        recentfile_basename was "RECENT-1h.yaml".

2008-08-08  Andreas Koenig  <k@andreas-koenigs-computer.local>

        * The test that was added in today's checkin is a good start for a test
        of rmirror. We should have more methods in Recent.pm: verify,
        addmissingfiles. We should verify the current tree, then rmirror it and
        then verifytree the copy. We could then add some arbitrary file and let
        it be discovered by addmissingfiles, then rmirror again and then
        verifytree the copy again.

        Then we could start stealing from csync2 sqlite database [no port to
        OSX!] and fill a local DB. And methods to compare the database with the
        recentfiles. Our strength is that in principle we could maintain state
        with a single float. We have synced up to 1234567890.123456. If the Z
        file does not add new files all we have to do is mirror the new ones and
        delete the goners.

        This makes it clear that we should extend current protocol and declare
        that we cheat when we add files too late, just to help the other end
        keeping track. Ah yes, that's what was meant when zloop was mentioned
        earlier.

        Maybe need to revisit File::Mirror to help me with this task.

2008-08-07  Andreas Koenig  <k@andreas-koenigs-computer.local>

        * There must be an allow-me-to-truncate flag in every recentfile.
        Without it one could construct a sequence of updates winning the locking
        battle against the aggregator. Only if an aggregator has managed to
        merge data over to the next level, truncating can be allowed. DONE with
        accessor merged.

2008-08-06  Andreas Koenig  <k@andreas-koenigs-computer.local>

        * We should probably guarantee that no duplicates enter the aggregator
        array.

2008-08-02  Andreas J. Koenig  <andreas.koenig.7os6VVqR@franz.ak.mind.de>

        * To get merge operation faster would need a good benchmark test. What
        02 spits out isn't reliable enough and is dominated by many other
        things. Between

        commit 10176bf6b79865d4fe9f46e3857a3b8669fa7961
        Author: Andreas J. Koenig <k@k75.(none)>
        Date:   Sat Aug 2 07:58:04 2008 +0200

        and

        commit 3243120a0c120aaddcd9b1f4db6689ff12ed2523
        Author: Andreas J. Koenig <k@k75.(none)>
        Date:   Sat Aug 2 11:40:29 2008 +0200

        there was a lot of trying but the effect is hardly measurable with
        current tests.  

        * overhead of connecting seems high. When setting
        max_files_per_connection to 1 we see that.

2008-08-01  Andreas J. Koenig  <andreas.koenig.7os6VVqR@franz.ak.mind.de>

        * 1217622571.0889 - 1217597432.86734 = 25138.2215600014

        25138.2215600014/3600 = 6.98283932222261

        It jumps into the eye that this is ~ 7 hours, not ~6, so there seems to
        be a bug in the aggregator. FIXED

2008-07-27  Andreas J. Koenig  <andreas.koenig.7os6VVqR@franz.ak.mind.de>

        * e.g. id/Y/YE/YEWENBIN/Emacs-PDE-0.2.16.tar.gz: Do we have it, should
        we have it, can we mirror it, mirror it!

        I fear this needs a new class which might be called
        File::Rsync::Mirror::Recent. It would collect all recentfiles of a kind
        and treat them as an entity. I realize that a single recentfile may be
        sufficient for certain tasks and that it is handy for the low level
        programmer but it is not nice to use. If there is a delete in the 1h
        file then the 6h file still contains it. Seekers of the best information
        need to combine at least some of the recentfiles most of the time.

        There is the place for the Z loop!

        But the combination is something to collect in a database, isn't it. Did
        csync2 just harrumph?

2008-07-26  Andreas J. Koenig  <andreas.koenig.7os6VVqR@franz.ak.mind.de>

        * it just occurred to me that hosts in the same mirroring pool could
        help out each other even without rewriting the recentfile. Just fetch
        the stuff to mirror from several places, bingo. But that's something
        that should rather live in a separate package or in rsync directly.

        * cronjobs are unsuited because with ntp they would all come at the full
        minute and disturb each other. Besides that I'd hate to have a backbone
        with more than a few seconds latency.

2008-07-25  Andreas J. Koenig  <andreas.koenig.7os6VVqR@franz.ak.mind.de>

        * a second rsync server with access control for PAUSE. Port? 873 is the
        standard port, let's take 8873.

        * if there were a filesystem based on this, it would have a slow access
        to inexistent files. It would probably provide wrong readdir (only based
        on current content) or also a slow one (based on a recentfile written
        after the call). But it would provide fast access to existing files. Or
        one would deliberately allow slightly blurred answers based on some
        sqlite reflection of the recentfiles.

        * todo: write a variant of mirror() that combines two or more
        recentfiles and treats them like one

        * todo: signal handler to remove the tempfile

2008-07-24  Andreas J. Koenig  <andreas.koenig.7os6VVqR@franz.ak.mind.de>

        * now that we have the symlink I forgot how it should be used in
        practice.

        * the z loop: add missing files to Z file. Just append them (instead of
        prepending). So one guy prepends something from the Y file from time to
        time and another guy appends something rather frequently. Collecting
        pond. When Y merges into Z, things get epoch and the collecting pond
        gets smaller. What exactly are "missing files"?

        take note of current epoch of the alpha file, let's call it the
        recent-ts

        find all files on disk

        remove all files registered in the recentworld up to recent-ts

        remove all files that have been deleted after recent-ts according to
        recentworld

2008-07-23  Andreas J. Koenig  <andreas.koenig.7os6VVqR@franz.ak.mind.de>

        * rersyncrecent might be a cronjob with a (locked) state file which
        contains things like after and maybe last z sync or such?

        rrr-mirror might be an alternative name but how would we justify the
        three Rs when there is no Re-Rsync-Recent?

        With the --loop parameter it is an endless loop, without it is no loop.
        At least this is simple.

        * todo: new accssor z-interval specifies how often the Z file is updated
        against the filesystem. We probably want no epoch stamp on these
        entries. And we want to be able to filter the entries (e.g. no
        by-modules and by-category tree)

2008-07-20  Andreas J. Koenig  <andreas.koenig.7os6VVqR@franz.ak.mind.de>

        * Fill the Z file. gc or fsck or both. Somehow we must get the old files
        into Z. We do not need the other files filled up with filesystem
        contents though.

        * need interface to query for a file in order to NOT call update on
        PAUSE a second time within a short time.

2008-07-19  Andreas J. Koenig  <andreas.koenig.7os6VVqR@franz.ak.mind.de>

        * recommended update interval? Makes no sense, is different for
        different users.

        * Moosify

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