issue_comments

I think I can tell what the current file limit is like so: ``` In [1]: import resource

In [2]: resource.getrlimit(resource.RLIMIT_NOFILE)
Out[2]: (256, 9223372036854775807) ``` So maybe I should have Datasette refuse to open more database files than that number minus 5 (to give me some spare room for opening CSS files etc).

I also eventually get this error: Traceback (most recent call last): File "/Users/simonw/Dropbox/Development/datasette/datasette/utils/asgi.py", line 121, in route_path return await view(new_scope, receive, send) File "/Users/simonw/Dropbox/Development/datasette/datasette/utils/asgi.py", line 336, in inner_static await asgi_send_file(send, full_path, chunk_size=chunk_size) File "/Users/simonw/Dropbox/Development/datasette/datasette/utils/asgi.py", line 303, in asgi_send_file async with aiofiles.open(str(filepath), mode="rb") as fp: File "/Users/simonw/.local/share/virtualenvs/datasette-oJRYYJuA/lib/python3.7/site-packages/aiofiles/base.py", line 78, in __aenter__ File "/Users/simonw/.local/share/virtualenvs/datasette-oJRYYJuA/lib/python3.7/site-packages/aiofiles/threadpool/__init__.py", line 35, in _open File "/usr/local/Cellar/python/3.7.5/Frameworks/Python.framework/Versions/3.7/lib/python3.7/concurrent/futures/thread.py", line 57, in run OSError: [Errno 24] Too many open files: '/Users/simonw/Dropbox/Development/datasette/datasette/static/app.css'

While running it against a nested directory with a TON of databases I kept seeing errors like this: Traceback (most recent call last): File "/Users/simonw/Dropbox/Development/datasette/datasette/utils/asgi.py", line 121, in route_path return await view(new_scope, receive, send) File "/Users/simonw/Dropbox/Development/datasette/datasette/utils/asgi.py", line 193, in view request, **scope["url_route"]["kwargs"] File "/Users/simonw/Dropbox/Development/datasette/datasette/views/index.py", line 58, in get tables[table]["num_relationships_for_sorting"] = count KeyError: 'primary-candidates-2018/rep_candidates' And Traceback (most recent call last): File "/Users/simonw/Dropbox/Development/datasette/datasette/utils/asgi.py", line 121, in route_path return await view(new_scope, receive, send) File "/Users/simonw/Dropbox/Development/datasette/datasette/utils/asgi.py", line 193, in view request, **scope["url_route"]["kwargs"] File "/Users/simonw/Dropbox/Development/datasette/datasette/views/index.py", line 58, in get tables[table]["num_relationships_for_sorting"] = count KeyError: 'space_used'

Here's the new utility function I should be using to verify database files that I find:

https://github.com/simonw/datasette/blob/6aa516d82dea9885cb4db8d56ec2ccfd4cd9b840/datasette/utils/init.py#L773-L787

I've figured out how to tell if a database is safe to open or not: sql select sql from sqlite_master where sql like 'CREATE VIRTUAL TABLE%'; This returns the SQL definitions for virtual tables. The bit after using tells you what they need.

Run this against a SpatiaLite database and you get the following: sql CREATE VIRTUAL TABLE SpatialIndex USING VirtualSpatialIndex() CREATE VIRTUAL TABLE ElementaryGeometries USING VirtualElementary() Run it against an Apple Photos photos.db file (found with find ~/Library | grep photos.db) and you get this (partial list): sql CREATE VIRTUAL TABLE RidList_VirtualReader using RidList_VirtualReaderModule CREATE VIRTUAL TABLE Array_VirtualReader using Array_VirtualReaderModule CREATE VIRTUAL TABLE LiGlobals_VirtualBufferReader using VirtualBufferReaderModule CREATE VIRTUAL TABLE RKPlace_RTree using rtree (modelId,minLongitude,maxLongitude,minLatitude,maxLatitude) For a database with FTS4 you get: sql CREATE VIRTUAL TABLE "docs_fts" USING FTS4 ( [title], [content], content="docs" ) FTS5: sql CREATE VIRTUAL TABLE [FARA_All_Registrants_fts] USING FTS5 ( [Name], [Address_1], [Address_2], content=[FARA_All_Registrants] ) So I can use this to figure out all of the using pieces and then compare them to a list of known support ones.

It think the fix is to use an old-fashioned threading module daemon thread directly. That should exit cleanly when the program exits.

https://gist.github.com/clchiou/f2608cbe54403edb0b13 might work.

Interesting new problem: hitting Ctrl+C no longer terminates the problem provided that scan_dirs() thread is still running.

https://stackoverflow.com/questions/49992329/the-workers-in-threadpoolexecutor-is-not-really-daemon has clues. The workers are only meant to exit when their worker queues are empty.

But... I want to run the worker every 10 seconds. How do I do that without having it loop forever and hence never quit?

... cheating like this seems to work: for name, db in list(self.ds.databases.items()): Python built-in operations are supposedly threadsafe, so in this case I can grab a copy of the list atomically (I think) and then safely iterate over it.

Seems to work in my testing. Wish I could prove it with a unit test though.

... or maybe I can cheat and wrap the access to self.ds.databases.items() in list(), so I'm iterating over an atomically-created list of those things instead? I'll try that first.

So I need to ensure the ds.databases data structure is manipulated in a thread-safe manner.

Mainly I need to ensure that it is locked during iterations over it, then unlocked at the end.

Trickiest part is probably ensuring there is a test that proves this is working - I feel like I got lucky encountering that RuntimeError as early as I did.

I tried running the scan_dirs() method in a thread and got an interesting error while trying to load the homepage: RuntimeError: OrderedDict mutated during iteration

Makes sense - I had a thread that added an item to that dictionary right while the homepage was attempting to run this code:

https://github.com/simonw/datasette/blob/efa54b439fd0394440c302602b919255047b59c5/datasette/views/index.py#L24-L27

Another problem: if any of the found databases use SpatiaLite then Datasette will fail to start at all.

It should skip them instead.

The select * from sqlite_master check apparently isn't quite enough to catch this case.

This can take a LONG time to run, and at the moment it's blocking and prevents Datasette from starting up.

It would be much better if this ran in a thread, or an asyncio task. Probably have to be a thread because there's no easy async version of pathlib.Path.glob() that I've seen.

One design issue: how to pick neat unique names for database files in a file hierarchy?

Here's what I have so far:

https://github.com/simonw/datasette/blob/fe6f9e6a7397cab2e4bc57745a8da9d824dad218/datasette/app.py#L231-L237

For these files: ../travel-old.db ../sf-tree-history/trees.db ../library-of-congress/records-from-df.db It made these names: travel-old sf-tree-history_trees library-of-congress_records-from-df Maybe this is good enough? Needs some tests.