"Too many open files" error running tests

[simonw]

I got this on my laptop:

...
/Users/simon/.local/share/virtualenvs/datasette-AWNrQs95/lib/python3.7/site-packages/jinja2/loaders.py:171: in get_source
    f = open_if_exists(filename)
_ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ 

filename = '/Users/simon/Dropbox/Development/datasette/datasette/templates/400.html', mode = 'rb'

    def open_if_exists(filename, mode='rb'):
        """Returns a file descriptor for the filename if that file exists,
        otherwise `None`.
        """
        try:
>           return open(filename, mode)
E           OSError: [Errno 24] Too many open files: '/Users/simon/Dropbox/Development/datasette/datasette/templates/400.html'

/Users/simon/.local/share/virtualenvs/datasette-AWNrQs95/lib/python3.7/site-packages/jinja2/utils.py:154: OSError

Based on the conversation in pytest-dev/pytest#2970 I'm worried that my tests are opening too many files without closing them.

In particular... I call sqlite3.connect(filepath) a LOT - and I don't ever call conn.close() on those opened connections:

datasette/datasette/database.py

Lines 58 to 60 in cf7a2bd

	return sqlite3.connect(
	"file:{}{}".format(self.path, qs), uri=True, check_same_thread=False
	)

Could this be resulting in my tests eventually opening too many unclosed file handles? How could I confirm this?

[simonw]

This shows currently open files (after pip install psutil):

import psutil
psutil.Process().open_files()

I ran it inside pytest -x --pdb and got this:

> /Users/simon/.local/share/virtualenvs/datasette-AWNrQs95/lib/python3.7/site-packages/jinja2/utils.py(154)open_if_exists()
-> return open(filename, mode)
(Pdb) import psutil
(Pdb) psutil.Process().open_files()
popenfile(path='/private/var/folders/wr/hn3206rs1yzgq3r49bz8nvnh0000gn/T/tmp9uhx5d8x/fixtures.db', fd=10),
popenfile(path='/private/var/folders/wr/hn3206rs1yzgq3r49bz8nvnh0000gn/T/tmpyfw44ica/fixtures.dot.db', fd=11),
popenfile(path='/private/var/folders/wr/hn3206rs1yzgq3r49bz8nvnh0000gn/T/tmpyrg6g48b/fixtures.db', fd=12),
popenfile(path='/private/var/folders/wr/hn3206rs1yzgq3r49bz8nvnh0000gn/T/tmp33kkg62s/fixtures.db', fd=13),
popenfile(path='/private/var/folders/wr/hn3206rs1yzgq3r49bz8nvnh0000gn/T/tmp33kkg62s/fixtures.db', fd=14),
popenfile(path='/private/var/folders/wr/hn3206rs1yzgq3r49bz8nvnh0000gn/T/tmp33kkg62s/fixtures.db', fd=15),
popenfile(path='/private/var/folders/wr/hn3206rs1yzgq3r49bz8nvnh0000gn/T/tmp33kkg62s/fixtures.db', fd=16),
popenfile(path='/private/var/folders/wr/hn3206rs1yzgq3r49bz8nvnh0000gn/T/tmp33kkg62s/fixtures.db', fd=17),
popenfile(path='/private/var/folders/wr/hn3206rs1yzgq3r49bz8nvnh0000gn/T/tmp33kkg62s/fixtures.db', fd=18),
popenfile(path='/private/var/folders/wr/hn3206rs1yzgq3r49bz8nvnh0000gn/T/tmp33kkg62s/fixtures.db', fd=19),
popenfile(path='/private/var/folders/wr/hn3206rs1yzgq3r49bz8nvnh0000gn/T/tmpng4lg84_/fixtures.db', fd=20),
popenfile(path='/private/var/folders/wr/hn3206rs1yzgq3r49bz8nvnh0000gn/T/tmp9uhx5d8x/fixtures.db', fd=21),
popenfile(path='/private/var/folders/wr/hn3206rs1yzgq3r49bz8nvnh0000gn/T/tmp9uhx5d8x/fixtures.db', fd=22),
popenfile(path='/private/var/folders/wr/hn3206rs1yzgq3r49bz8nvnh0000gn/T/tmp9uhx5d8x/fixtures.db', fd=23),
popenfile(path='/private/var/folders/wr/hn3206rs1yzgq3r49bz8nvnh0000gn/T/tmph11oalw_/fixtures.db', fd=24),
popenfile(path='/private/var/folders/wr/hn3206rs1yzgq3r49bz8nvnh0000gn/T/tmpyfw44ica/fixtures.dot.db', fd=25),
popenfile(path='/private/var/folders/wr/hn3206rs1yzgq3r49bz8nvnh0000gn/T/tmpyfw44ica/fixtures.dot.db', fd=26),
popenfile(path='/private/var/folders/wr/hn3206rs1yzgq3r49bz8nvnh0000gn/T/tmpyfw44ica/fixtures.dot.db', fd=27),
popenfile(path='/private/var/folders/wr/hn3206rs1yzgq3r49bz8nvnh0000gn/T/tmpiorb2bo9/fixtures.db', fd=28),
popenfile(path='/private/var/folders/wr/hn3206rs1yzgq3r49bz8nvnh0000gn/T/tmpyrg6g48b/fixtures.db', fd=29),
popenfile(path='/private/var/folders/wr/hn3206rs1yzgq3r49bz8nvnh0000gn/T/tmpyrg6g48b/fixtures.db', fd=30),
popenfile(path='/private/var/folders/wr/hn3206rs1yzgq3r49bz8nvnh0000gn/T/tmpyrg6g48b/fixtures.db', fd=31),
popenfile(path='/private/var/folders/wr/hn3206rs1yzgq3r49bz8nvnh0000gn/T/tmprvyj5udv/fixtures.db', fd=32),
popenfile(path='/private/var/folders/wr/hn3206rs1yzgq3r49bz8nvnh0000gn/T/tmpng4lg84_/fixtures.db', fd=33),
popenfile(path='/private/var/folders/wr/hn3206rs1yzgq3r49bz8nvnh0000gn/T/tmpng4lg84_/fixtures.db', fd=34),
popenfile(path='/private/var/folders/wr/hn3206rs1yzgq3r49bz8nvnh0000gn/T/tmpng4lg84_/fixtures.db', fd=35),
popenfile(path='/private/var/folders/wr/hn3206rs1yzgq3r49bz8nvnh0000gn/T/tmpb_l6gmq0/fixtures.db', fd=36),
popenfile(path='/private/var/folders/wr/hn3206rs1yzgq3r49bz8nvnh0000gn/T/tmph11oalw_/extra database.db', fd=40),
popenfile(path='/private/var/folders/wr/hn3206rs1yzgq3r49bz8nvnh0000gn/T/tmpf0py4thp/fixtures.db', fd=41),
popenfile(path='/private/var/folders/wr/hn3206rs1yzgq3r49bz8nvnh0000gn/T/tmpiorb2bo9/fixtures.db', fd=42),
popenfile(path='/private/var/folders/wr/hn3206rs1yzgq3r49bz8nvnh0000gn/T/tmpiorb2bo9/fixtures.db', fd=43),
popenfile(path='/private/var/folders/wr/hn3206rs1yzgq3r49bz8nvnh0000gn/T/tmpiorb2bo9/fixtures.db', fd=44),
popenfile(path='/private/var/folders/wr/hn3206rs1yzgq3r49bz8nvnh0000gn/T/tmph11oalw_/fixtures.db', fd=45),
popenfile(path='/private/var/folders/wr/hn3206rs1yzgq3r49bz8nvnh0000gn/T/tmph11oalw_/fixtures.db', fd=52),
popenfile(path='/private/var/folders/wr/hn3206rs1yzgq3r49bz8nvnh0000gn/T/tmpwgcnmg4b/fixtures.db', fd=53),
popenfile(path='/private/var/folders/wr/hn3206rs1yzgq3r49bz8nvnh0000gn/T/tmprvyj5udv/fixtures.db', fd=54),
popenfile(path='/private/var/folders/wr/hn3206rs1yzgq3r49bz8nvnh0000gn/T/tmprvyj5udv/fixtures.db', fd=55),
popenfile(path='/private/var/folders/wr/hn3206rs1yzgq3r49bz8nvnh0000gn/T/tmprvyj5udv/fixtures.db', fd=56),
popenfile(path='/private/var/folders/wr/hn3206rs1yzgq3r49bz8nvnh0000gn/T/tmpoveuwqn6/fixtures.db', fd=57),
popenfile(path='/private/var/folders/wr/hn3206rs1yzgq3r49bz8nvnh0000gn/T/tmpb_l6gmq0/fixtures.db', fd=61),
popenfile(path='/private/var/folders/wr/hn3206rs1yzgq3r49bz8nvnh0000gn/T/tmpb_l6gmq0/fixtures.db', fd=62),
popenfile(path='/private/var/folders/wr/hn3206rs1yzgq3r49bz8nvnh0000gn/T/tmpb_l6gmq0/fixtures.db', fd=63),
popenfile(path='/private/var/folders/wr/hn3206rs1yzgq3r49bz8nvnh0000gn/T/tmp_j4h9mrn/fixtures.db', fd=64),
popenfile(path='/private/var/folders/wr/hn3206rs1yzgq3r49bz8nvnh0000gn/T/tmpf0py4thp/fixtures.db', fd=65),
popenfile(path='/private/var/folders/wr/hn3206rs1yzgq3r49bz8nvnh0000gn/T/tmpf0py4thp/fixtures.db', fd=66),
popenfile(path='/private/var/folders/wr/hn3206rs1yzgq3r49bz8nvnh0000gn/T/tmpf0py4thp/extra database.db', fd=67),
popenfile(path='/private/var/folders/wr/hn3206rs1yzgq3r49bz8nvnh0000gn/T/tmpf0py4thp/extra database.db', fd=68),
popenfile(path='/private/var/folders/wr/hn3206rs1yzgq3r49bz8nvnh0000gn/T/tmpf0py4thp/fixtures.db', fd=69),
popenfile(path='/private/var/folders/wr/hn3206rs1yzgq3r49bz8nvnh0000gn/T/tmpf0py4thp/extra database.db', fd=70)
 popenfile(path='/private/var/folders/wr/hn3206rs1yzgq3r49bz8nvnh0000gn/T/tmpub3eodj1/fixtures.db', fd=71)
 popenfile(path='/private/var/folders/wr/hn3206rs1yzgq3r49bz8nvnh0000gn/T/tmpwgcnmg4b/fixtures.db', fd=72)
 popenfile(path='/private/var/folders/wr/hn3206rs1yzgq3r49bz8nvnh0000gn/T/tmpwgcnmg4b/foo.db', fd=73)
 popenfile(path='/private/var/folders/wr/hn3206rs1yzgq3r49bz8nvnh0000gn/T/tmpwgcnmg4b/foo.db', fd=74)
 popenfile(path='/private/var/folders/wr/hn3206rs1yzgq3r49bz8nvnh0000gn/T/tmpwgcnmg4b/fixtures.db', fd=75)
 popenfile(path='/private/var/folders/wr/hn3206rs1yzgq3r49bz8nvnh0000gn/T/tmpwgcnmg4b/fixtures.db', fd=76)
 popenfile(path='/private/var/folders/wr/hn3206rs1yzgq3r49bz8nvnh0000gn/T/tmpwgcnmg4b/foo.db', fd=77)
 popenfile(path='/private/var/folders/wr/hn3206rs1yzgq3r49bz8nvnh0000gn/T/tmpwgcnmg4b/foo-bar.db', fd=78)
 popenfile(path='/private/var/folders/wr/hn3206rs1yzgq3r49bz8nvnh0000gn/T/tmpwgcnmg4b/foo-bar.db', fd=79)
 popenfile(path='/private/var/folders/wr/hn3206rs1yzgq3r49bz8nvnh0000gn/T/tmpwgcnmg4b/foo-bar.db', fd=80)
 popenfile(path='/private/var/folders/wr/hn3206rs1yzgq3r49bz8nvnh0000gn/T/pytest-of-simon/pytest-4/config-dir0/immutable.db', fd=81),
popenfile(path='/private/var/folders/wr/hn3206rs1yzgq3r49bz8nvnh0000gn/T/tmpoveuwqn6/fixtures.db', fd=82),
popenfile(path='/private/var/folders/wr/hn3206rs1yzgq3r49bz8nvnh0000gn/T/tmpoveuwqn6/fixtures.db', fd=83),
popenfile(path='/private/var/folders/wr/hn3206rs1yzgq3r49bz8nvnh0000gn/T/tmpoveuwqn6/fixtures.db', fd=84),
popenfile(path='/private/var/folders/wr/hn3206rs1yzgq3r49bz8nvnh0000gn/T/tmp44w5d5wo/fixtures.db', fd=85),
popenfile(path='/private/var/folders/wr/hn3206rs1yzgq3r49bz8nvnh0000gn/T/tmp_j4h9mrn/fixtures.db', fd=86),
popenfile(path='/private/var/folders/wr/hn3206rs1yzgq3r49bz8nvnh0000gn/T/tmp_j4h9mrn/fixtures.db', fd=87),
popenfile(path='/private/var/folders/wr/hn3206rs1yzgq3r49bz8nvnh0000gn/T/tmp_j4h9mrn/fixtures.db', fd=88),
popenfile(path='/private/var/folders/wr/hn3206rs1yzgq3r49bz8nvnh0000gn/T/tmpvu7h14uy/fixtures.db', fd=89),
popenfile(path='/private/var/folders/wr/hn3206rs1yzgq3r49bz8nvnh0000gn/T/pytest-of-simon/pytest-4/config-dir0/demo.db', fd=119),
popenfile(path='/private/var/folders/wr/hn3206rs1yzgq3r49bz8nvnh0000gn/T/pytest-of-simon/pytest-4/config-dir0/demo.db', fd=120),
popenfile(path='/private/var/folders/wr/hn3206rs1yzgq3r49bz8nvnh0000gn/T/pytest-of-simon/pytest-4/config-dir0/demo.db', fd=121),
popenfile(path='/private/var/folders/wr/hn3206rs1yzgq3r49bz8nvnh0000gn/T/tmp0xcnrjag/fixtures.db', fd=122),
popenfile(path='/private/var/folders/wr/hn3206rs1yzgq3r49bz8nvnh0000gn/T/tmpub3eodj1/fixtures.db', fd=123),
popenfile(path='/private/var/folders/wr/hn3206rs1yzgq3r49bz8nvnh0000gn/T/tmpub3eodj1/fixtures.db', fd=124),
popenfile(path='/private/var/folders/wr/hn3206rs1yzgq3r49bz8nvnh0000gn/T/tmpub3eodj1/fixtures.db', fd=125),
popenfile(path='/private/var/folders/wr/hn3206rs1yzgq3r49bz8nvnh0000gn/T/tmpfz8go8rk/fixtures.db', fd=126),
popenfile(path='/private/var/folders/wr/hn3206rs1yzgq3r49bz8nvnh0000gn/T/tmp44w5d5wo/fixtures.db', fd=127),
popenfile(path='/private/var/folders/wr/hn3206rs1yzgq3r49bz8nvnh0000gn/T/tmp44w5d5wo/fixtures.db', fd=128),
popenfile(path='/private/var/folders/wr/hn3206rs1yzgq3r49bz8nvnh0000gn/T/tmp44w5d5wo/fixtures.db', fd=129),
popenfile(path='/private/var/folders/wr/hn3206rs1yzgq3r49bz8nvnh0000gn/T/tmp5j3k1ep_/fixtures.db', fd=130)
 popenfile(path='/private/var/folders/wr/hn3206rs1yzgq3r49bz8nvnh0000gn/T/tmpvu7h14uy/fixtures.db', fd=131),
popenfile(path='/private/var/folders/wr/hn3206rs1yzgq3r49bz8nvnh0000gn/T/tmpvu7h14uy/fixtures.db', fd=132),
popenfile(path='/private/var/folders/wr/hn3206rs1yzgq3r49bz8nvnh0000gn/T/tmpvo3cobk9/fixtures.db', fd=133),
popenfile(path='/private/var/folders/wr/hn3206rs1yzgq3r49bz8nvnh0000gn/T/tmp2t9txyir/fixtures.db', fd=134),
popenfile(path='/private/var/folders/wr/hn3206rs1yzgq3r49bz8nvnh0000gn/T/tmpfz8go8rk/fixtures.db', fd=135),
popenfile(path='/private/var/folders/wr/hn3206rs1yzgq3r49bz8nvnh0000gn/T/tmpfz8go8rk/fixtures.db', fd=136),
popenfile(path='/private/var/folders/wr/hn3206rs1yzgq3r49bz8nvnh0000gn/T/tmp7h3skv8b/fixtures.db', fd=137),
popenfile(path='/private/var/folders/wr/hn3206rs1yzgq3r49bz8nvnh0000gn/T/tmp5j3k1ep_/fixtures.db', fd=138),
popenfile(path='/private/var/folders/wr/hn3206rs1yzgq3r49bz8nvnh0000gn/T/tmp5j3k1ep_/fixtures.db', fd=139),
popenfile(path='/private/var/folders/wr/hn3206rs1yzgq3r49bz8nvnh0000gn/T/tmp5j3k1ep_/fixtures.db', fd=140),
popenfile(path='/private/var/folders/wr/hn3206rs1yzgq3r49bz8nvnh0000gn/T/tmp5j3k1ep_/extra database.db', fd=141),

So yeah, that's too many open files!

[simonw]

That's 91 open files but only 29 unique filenames.

[simonw]

I tried this experiment:

import sqlite3, psutil
def show_things():
    conn = sqlite3.connect("fixtures.db")
    tables = [r[0] for r in conn.execute("select * from sqlite_master").fetchall()]
    return tables
print(psutil.Process().open_files())
print(show_things())
print(psutil.Process().open_files())

To see if the connection would be automatically released when the conn variable was garbage collected at the end of the function... and it was correctly released - the two calls to open_files() showed that the file did not remain open.

Likewise:

In [11]: conn = sqlite3.connect("fixtures.db")                                                                                                                                                                    

In [12]: psutil.Process().open_files()                                                                                                                                                                            
Out[12]: 
[popenfile(path='/Users/simon/.ipython/profile_default/history.sqlite', fd=4),
 popenfile(path='/Users/simon/.ipython/profile_default/history.sqlite', fd=5),
 popenfile(path='/Users/simon/Dropbox/Development/datasette/fixtures.db', fd=12)]

In [13]: del conn                                                                                                                                                                                                 

In [14]: psutil.Process().open_files()                                                                                                                                                                            
Out[14]: 
[popenfile(path='/Users/simon/.ipython/profile_default/history.sqlite', fd=4),
 popenfile(path='/Users/simon/.ipython/profile_default/history.sqlite', fd=5)]

So presumably there's something about the way my pytest fixtures work that's causing the many different Datasette() instances and their underlying SQLite connections that I create not to be cleaned up later.

[simonw]

Released a new plugin, datasette-psutil, as a side-effect of this investigation: https://github.com/simonw/datasette-psutil

[simonw]

Idea: num_sql_threads (described as "Number of threads in the thread pool for executing SQLite queries") defaults to 3 - can I knock that down to 1 in the tests and open less connections as a result?

[simonw]

That seems to have fixed the problem, at least for the moment.