Re: Portable version degrading


 

Hi,
Config files and log files are not the only thing NVDA will need to access from disks. Others include various DLL files, one or more executables and what not.
Cheers,
Joseph

-----Original Message-----
From: nvda@nvda.groups.io [mailto:nvda@nvda.groups.io] On Behalf Of Didier Colle
Sent: Friday, January 19, 2018 5:47 PM
To: nvda@nvda.groups.io
Subject: Re: [nvda] Portable version degrading

Dear Joseph,


On 20/01/2018 1:21, Joseph Lee wrote:
Hi,
Fragmentation will happen as long as new information is written in places that'll cause problems for fast reading later. Also, while something is running, the operating system will still need to access things on disk if asked by the program.
sure, of course.

Question:
Roger already answered that even with add-ons disabled sluggishness and weird behavior remains.
Thus what does nvda core (or at least non add-on related code) ask the OS to access on disc while being executed? Screen reading, the main function of nvda, seems to me to have very little to do with disc access (except writing logs and reading configuration (which is probably loaded in RAM anyway).

Kind regards,

Didier

As for swapping configurations: in theory, yes as long as the versions are compatible enough to not cause visible side effects. For example, if one swaps configurations between stable and next branches, that could raise problems in that some things required by next snapshots might not be present.
As for the add-on being the culprit: could be. One thing to try though: what if Roger runs his portable copy with all add-ons disabled? If that improves performance, then it could be an add-on, if not, we should try something else.
Implicating file systems: Roger did say this is an internal drive, hence I put more weight on possible fragmentation and data movement issues.
Cheers,
Joseph

-----Original Message-----
From: nvda@nvda.groups.io [mailto:nvda@nvda.groups.io] On Behalf Of
Didier Colle
Sent: Friday, January 19, 2018 3:40 PM
To: nvda@nvda.groups.io
Subject: Re: [nvda] Portable version degrading

Dear Joseph, roger, all,


@Joseph: not sure to understand what point you try to make. Is your suggestion there is indeed a filesystem problem as the root cause?


trying to recapitulate a few things:

* "it can make it appear that the add on is defective or has a bug
while it really doesn't."

@Roger: for any further meaningful diagnosis, I believe a more
concrete symptom description is needed? (how does such "would be" bug
manifestate itself? Is it always the same "would be" bug or do many
"would be" bugs appear randomly? when do such "would be" bugs appear
(during loading, during execution of the add-on)?)

* "there's no file system errors"

I guess that means there are no issues with the
physical/electronic/magnetic integrity of the storage medium itself
(or that the filesystem has set them aside such that they are not used
anymore). In case corrupted/broken blocks on the storage medium would
be the root cause, something should be found in the logs as loading
the relevant python modules should throw an exception (if these
exceptions are not logged, it should be possible to do so). Therefore,
I dismiss storage medium/filesystem corruption as root cause of the
above mentioned "would be" bugs (assuming bugs have to be interpreted
as broken functionality).


* "I also notice a few functions of nvda either don't work at all or
nvda gets very sluggish in responsiveness"
@Roger: again, for any meaningfull diagnosis, provide a more concrete
symptiom description. What functions are you exactly speaking about?
What does "not work at all" exactly mean: do you mean sluggishness
with extremely long / infinite response times? Or do you get errors? or ...
Is the sluggishness general or does it happen in those specific
functions? What do you mean by sluggishness: response in only a second?
A few seconds? A minute or more? When does sluggishness happen: at
time of loading add-on/modules or continuously or ...?
* "... nor any fragmenting.". Statement from Joseph: "In case of
Roger's
issue: a possible contributing factor is constant add-on updates. He
uses an add-on that is updated on a regular basis, .. ..., potentially
fragmenting bits of files ..."
The two statements appear to me as contradictory. Fragmentation may be
a root cause of sluggishness, but only when access to storage medium
is needed and not during general execution which typically takes place
from RAM rather then from disc. Therefore, fragmentation issues appear
very unlikely to me.

* "while the installed version is always stable as a rock." and "I use
the portable copy to test a couple add ons"
@Roger: how much do you use one and the other? How much usage does it
take before the portable copy gets degraded?
The two statements suggest there is a problem with the portable copies.
However, there seems to be nobody else experiencing the same problem.
Thus, I would translate this into the following question that you
would need to test/investigage further: is there a conflict between
the portable copies and your specific system setup, or is the issue
caused by the add-ons under test?
To test the former possibility, why not using a fresh portable copy
replicating the setup of your installed version instead of that
installed version for a while?
To test the latter that would probably require moving the add-on
testing to the installed version: I guess you are using the portable
version for this purpose, exactly to avoid messing up the installed
version. Would you have the possibility to do the testing in for
example a virtual machine, such that you can test on an installed
instead of a portable copy version, while not messing up your main system with this testing?
Joseph, anyone else: is there a (possibly more cumbersome) way to
perform testing on an installed version while keeping at all times a
possibility to revert back to a stable/clean situation? (e.g., having
a .bat script that swaps configuration file and add-on directories
between stable and testing versions and that can easily be executed in
between exiting nvda and restarting it?) In case none of the above
options is tried, my suggestions would be then to regularly take
snapshot copies of your portable copy such that when degradation takes
place a diff between stable and degraded version can be taken and
investigated.

In summary, I believe:
1) a much more concrete/detailed/... symptom description is needed
before any meaningful statements regarding diagnosis is possible;
2) with the info I have, filesystem/storage medium
problems/corruptions are very unlikely.
3) further testing/investigation is needed in order to support/dismiss
certain hypotheses.

Kind regards,

Didier

On 19/01/2018 18:19, Joseph Lee wrote:
Hi,
It'll depend on what type of drive it is. If it's a traditional hard
drive, it'll degrade as data moves around, creating the need for defragmentation.
This is especially the case when data is repeatedly written and the
file system is asked to find new locations to hold the constantly changing data.
In case of solid-state drives, it'll degrade if the same region is
written repeatedly, as flash memory has limited endurance when it
comes to data reads and writes.
In case of Roger's issue: a possible contributing factor is constant
add-on updates. He uses an add-on that is updated on a regular basis,
putting strain on part of the drive where the add-on bits are stored.
Thus, some drive sectors are repeatedly bombarded with new
information, and one way operating systems will do in this case is
move the new data somewhere else on the drive, potentially
fragmenting bits of files (I'll explain in a moment). Thus one
solution is to not test all add-on updates, but that's a bit risky as
Roger is one of the key testers for this add-on I'm talking about.
Regarding fragmentation and what not: the following is a bit geeky
but I believe you should know about how some parts of a file system
(an in extension, operating systems) works, because I believe it'll
help folks better understand what might be going on:
Storage devices encountered in the wild are typically organized into
many parts, typically into blocks of fixed-length units called
"sectors". A sector is smallest unit of information that the storage
device can present to the outside world, as in how much data can be held on a storage device.
For example, when you store a small document on a hard disk drive
(HDD) and when you wish to open it in Notepad, Windows will ask a
module that's in charge of organizing and interpreting data on a
drive (called a file system) to locate the sector where the document
(or magnets or flash cells that constitute the document data) is
stored and bring it out to you. To you, all you see is the path to
the document, but the file system will ask the drive controller (a
small computer inside hard disks and other storage devices) to fetch
data in a particular sector or region. Depending on what kind of
storage medium you're dealing with, reading from disks may involve
waiting for a platter with desired sector to come to the attention of
a read/write head (a thin magnetic sensor used to detect or make
changes to magnetic
fields) or peering inside windows and extracting electrons trapped within.
This last sentence is a vivid description of how hard disks and
solid-state drives really work behind the scenes, respectively.
But storage devices are not just meant for reading things for your
enjoyment. Without means of storing new things, it becomes useless.
Depending on the medium you've got, when you save something to a
storage device, the file system in charge of the device will ask the
drive controller to either find a spot on a disk filled with magnets
and change some magnets, or apply heat pressure to dislodge all cells
on a block, erase the block, add new things, and fill the empty block
with modified data (including old bits). You can imagine how tedious
this can get, but as far as your work is concerned, it is safe and sound.
Now imagine you wish to read and write repeatedly on a storage
device. The file system will repeatedly ask the drive hardware to
fetch data from specific regions, and will look for new locations to
store changes. On a hard drive, because there are limited number of
heads and it'll take a while for desired magnetic region to come to
attention of one, read speed is slow, hence increased latency
(latency refers to how long you have to wait for something to
happen). When it comes to saving things to HDD's, all the drive needs
to do is tell the read/write head to change some magnets wherever it
wishes, hence data overriding is possible and easy. But operating systems (rather, file systems) are smarter than that, as we'll see below.
In case of solid-state drives, reading data is simple as looking up
the address (or sector) where the electrons comprising the data you
want is saved (akin to walking down a street grid), so no need to
wait for a sensor to wait for something to happen. This is the reason
why solid-state drives appear to respond fast when reading something.
On the other hand, writing or injecting electrons is very slow
because the drive needs to erase the entire block before writing new
data. In other words, just changing a letter in a document and saving
it to an SSD involves a lot of work, hence SSD's are slower when it
comes to writing new things, but because of the underlying technology in use, it is way faster than hard disks.
As hinted above, file systems are smarter than drive controllers to
some extent. If data is written to a drive, the drive controller will
process whatever it comes along its path. But file systems won't let
drive controllers get away with that: file systems such as NTFS (New
Technology File System) will schedule data writes so it'll have
minimal impact on the lifespan of a storage device. For hard disks,
it'll try its best to tell the drive to store file data in
consecutive locations in one big batch, but that doesn't always work.
For SSD's, the file system will ask the drive to storage new
information in different cells so all regions can be used equally (at
least for storing new information; this is called ware leveling). One
way to speed things up is asking the drive to reorganize data so file
fragments can be found in consecutive sectors or trim deleted regions
so fresh information can be written to more blocks (for HDD's and
SSD's, respectively), and this operation itself is tedious and produce bad results if not done correctly and carefully.

I do understand the above explanation is a bit geeky, but I believe
you need to know some things about how things work. It is also a
personal exercise to refresh my memory on certain computer science
topics (I majored in it not long ago, and my interests were mostly
hardware and operating systems, hence I was sort of naturally drawn
to screen reader internals and how it interacts with system software).
Cheers,
Joseph

-----Original Message-----
From: nvda@nvda.groups.io [mailto:nvda@nvda.groups.io] On Behalf Of
Roger Stewart
Sent: Friday, January 19, 2018 7:58 AM
To: nvda@nvda.groups.io
Subject: Re: [nvda] Portable version degrading

The problem with this discussion is my portable version is on an
internal hard drive. So why is this degrading?

Nothing else on this drive has any trouble and I've checked, and
there's no file system errors nor any fragmenting.


Roger












On 1/19/2018 8:28 AM, Antony Stone wrote:
USB drives do need to be unmounted before removing them, otherwise
there
is
the risk of file system corruption. Precisely the same is true for
external
hard drives, floppy disks, or any other writeable medium you can
temporarily
attach to a computer.

I've never seen a USB thumb drive fall apart, and I think they're
considerably
more robust than floppy disks, which is basically what they
replaced. You
can
also drop them on the floor with a good deal more confidence of them
working
afterwards than if you drop an external hard disk.

Yes, they're vulnerable to static electricity; that's why most of
them
have
plastic caps to put over the contacts or a slider to retract the
contacts
into
the body.

My experience is that if they're treated reasonably they work very well.
If
they're mistreated they'll give as many problems as any other
mistreated storage medium.


Antony.

On Friday 19 January 2018 at 15:17:36, tonea.ctr.morrow@faa.gov wrote:

A few years back, I had a job for three years where people brought
me
their
files on USB thumb drives. These things are horrible in terms of
long-life. The really do have to be unmounted prior to removing
from the computer or they get corrupted. They physically fall apart
easily. And, the hardware inside seems to be more vulnerable to
static electricity
data
loss than other portable drives, certainly more vulnerable than
most computers.



I would think that would be the problem.



Tonea



-----Original Message-----

I've noticed over the past couple years that my portable install of
nvda will sometimes degrade or get a bit corrupted over time all by
itself while the installed version is always stable as a rock.
Does anyone know why this is and is there any way to prevent this
from happening? I use the portable copy to test a couple add ons
and if the portable version corrupts, it can make it appear that
the add on is defective or has a bug while it really doesn't.
Deleting the portable copy and making a new one will clear it up.
I also notice a few functions of nvda either don't
work
at all or nvda gets very sluggish in responsiveness and this all
gets
back
to normal after a complete flush and remake of the portable
version. As
I
say, this never has happened at all with my installed copy on the
same computer.





Roger








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