I'm experimenting with enabling the shared cache in a SQLite implementation I'm working on. In the actual app everything works fine, but my unit tests are now failing with "disk I/O error"s. I'm assuming this is because the shared cache is making assumptions about the file that are no longer valid once it's been deleted.
How can I clear out this shared cache data? I've tried running sqlite3_shutdown() followed by sqlite3_initialize() but the problems persist.
I've actually discovered that some of my tests weren't closing connections properly, and that was the source of my problem - shared-cache was just highlighting it (though I'm not 100% sure why).
That said, in my journey, I did manage to find a way to control where SQLite puts its temporary files. the sqlite3_temp_directory global variable lets you define it - by default it's blank and defers to the OS, I think.
If you set that directory you can manually clear out any files whenever you wish.
Related
Does anyone know of a way that I can tell rsync to not perform a backup if it detects and X amount of data will be changed? For example, if I run a backup and it detects and 25% of the data in the destination directory will be changed can I have it automatically abort that run and then I can evaluate and make a decision whether allow it or not. I back up my machine every night but what I'm worried about is if my machine gets hit with a ransomware bug or another issue that causes a ton of my data gets destroyed or lost I really don't want it to propagate to my backup. I used to tool call synconvery and it had this feature but I don't think the tool is supported very well and I get a lot of permission and read errors that I don't see with any other tools. Goodsync also has this feature but even though it runs on the Mac it doesn't support special characters in a file name and replaces it with an underscore when the file is copied. I just think that will cause problems when I try to restore those file and it's being referenced wit that special character but can't be found because it has a damn underscore. I like using rsync and I will eventually retrofit my script to use msrsync but I can't trust it if I can't get this protection in place.
I am new in Symfony2 and I am working in a project in the prod environment.
I changed a twig file so it looks like I have to clean the cache to update the page.
There is any risk at cleaning the cache of the project?
It is possible that I am going to lost any important file?
If yes, there is a way to make this update of some safer way?
Short answer: yes, it can be dangerous. No, there's no safer way. You should take a backup of the whole application root (cache included).
Details
The cache folder contains "compiled" files. Unless someone is doing something very wrong, it does not contains important files. And - even if it does - it would probably be quite complex to get them out from cache.
So at first glance you should be able to delete the cache anytime you want without fear.
Cache version
There's a small catch: you cannot be sure that - even before your changes - the current cache is sync with the current source code.
If, previously, someone made changes to the application but did not clear the cache, those changes are not actually used in production.
In this case, when you clear the cache all such changes will be released as well as your change.
Suggestion
Right now the only way is forward, so you have to clear the cache. But you may want to:
backup first
get a list of more recent changes to source code
do the task when you have time to test and fix if something comes up
In the long term, you should use a deploy script / system to make sure that the cache is automatically cleared any time some changes to source code is delivered.
In an AIR app you can use SQLite via the flash.data classes. It appears that by default the encoding of the database created is set to UTF-16le, which means that textual data is stored with two bytes per character, resulting in a nearly 100% overhead for ASCII-heavy database content.
The default for a SQLite database is UTF-8, assuming the shell program (sqlite3) is indicative. Presumably Adobe has decided to override this for some reason, but I'd prefer not to suffer the wasted storage space if possible.
A PRAGMA encoding = "UTF-8"; statement prior to writing anything to the database would normally resolve the issue, but it appears that's not allowed in AIR either.
My workaround for now is to use a "template.db" that I create ahead of time and bundled into the application. In this template.db I've set the encoding to UTF-8 manually. If the database file does not exist already when my program starts, I create it by copying that template to my database file, then proceed to open and use it normally. I've confirmed that TEXT data is then stored as UTF-8, as desired.
I haven't seen any ill effects yet, but this is hackish. Is there a better way to set the encoding to UTF-8? Or is it a Bad Idea for some reason?
With no other workarounds or answers found, I'm posting my workaround as the Answer. It worked fine in a PlayBook app for the last two years, so presumably has no unforeseen side-effects, at least in that environment:
My workaround for now is to use a "template.db" that I create ahead of time and bundled into the application. In this template.db I've set the encoding to UTF-8 manually. If the database file does not exist already when my program starts, I create it by copying that template to my database file, then proceed to open and use it normally. I've confirmed that TEXT data then now stored as UTF-8 as desired.
you may check the execution source file of the project like /bin/debug in C# Visual Studio projects.
The changed committed is not necessarily be executed in your db located in other folders.
Everything I have read so far, it seems as though you copy the DB from assets to a "working directory" before it is used. If I have an existing SQLite DB I put it in assets. Then I have to copy it before it is used.
Does anyone know why this is the case?
I can see a possible application to that, where one doesn't want to accidentally corrupt database during write. But in that case, one would have to move database back when it's done working on it, otherwise, next time program is run will start from "default" database state.
That might be another use case - you might always want to start program execution with known data state. Previous state might be set from external application.
Thanks everyone for your ideas.
I think what I might have figured out is that the install cannot put a DB directly to the /data directory.
In Eclipse there is no /data which is where most of the discussions I have read say to put it.
This is one of the several I found:
http://www.reigndesign.com/blog/using-your-own-sqlite-database-in-android-applications/comment-page-4/#comment-37008
Suppose I have a file, urls.txt, that contains a list of URLs I'm monitoring. My monitoring script edits that file occasionally, say, to indicate whether each URL is reachable. I'd like to also manually edit that file, to add to or change the list of URLs. How can I allow that such that I don't have to think about it when manually editing?
Here are some possible answers. What would you do?
Engage in hackery like having the program check for the lockfiles that vim or emacs create. Since this is just for me, this would actually work.
If the human edits always take precedence, just always have the human clobber the program's changes (eg, ignore the editor's warning that the file has changed on disk). The program can then just redo its changes on its next loop. Still, changing the file while the user edits it is not so nice.
Never let a human touch a file that a program makes ongoing modifications to. Rethink the design and have one file that only the human edits and another file that only the program edits.
Give the human a custom tool to edit the file that does the appropriate file locking. That could be as crude as locking the file and then launching an editor, or a custom interface (perhaps a simple command line interface) for inserting/changing/deleting entries from the file.
Use a database instead of a flat file and then the locking is all taken care of automatically.
(Note that I concocted the URL monitoring example to make this more concrete and because what I actually have in mind is perhaps too weird and distracting -- this question is strictly about how to let humans and programs both modify the same state file.)
I'd use a database since that's basically what you're going to have to build to achieve what you want. Why re-invent the wheel?
If a full-blown DBMS is too much of a load, separate the files into two and synchronize them periodically. Whether the URL is reachable doesn't sound like something the user would be changing, so should not be editable by them.
During the synchronize process (which would have to lock out the monitor and the user although it could be a sub-function of the monitor), remove entries in the monitor file that aren't in the user full. Also, add to the monitor file those that have been added to the user file (and start monitoring them).
But, I'd go the database method with a special front-end for the user, since you can get relatively good light-weight databases nowadays.
Use a sensible version control system!
(Git would work well here).
That said, the nature of the problem implies that a real database would be best - and they will generally have either database-level, table-level, or row-level locking - but then put any scripts you need into version control.
I would go with option 3. In fact, I would have the program read the human-edited input file, and append the results of each query to a log file. In this way, you can also analyse the reachability of sites over time. You can also have the program maintain a file that indicates the current reachability state of each site in the input file, as a snapshot of the current state.
One other option is using two files, one for automated access and one for manual. You'd need a way in the user file to indicate modifications or deletions but you'd have similar problems in some of the other solutions as well.