SQLite occasionally fails to create :memory: database - ios

Question

In our unit testing suite, we create and destroy a large number of SQLite databases that use the path of ":memory:". Occasionally, and only when running on the iOS simulator, the creation of those databases fails with the rather enigmatic message:
Database ":memory:": unable to open database file
99% of the time, these requests succeed. (Subsequent tests within the same test run typically succeed after this failure occurs.) But when you're using this in an automated build-acceptance test, you want 100%.
We've instrumented for memory consumption (it's within normal limits) and disk-space availability (20GB+ available).
Any ideas?
UPDATE: Captured this happening with extra logging per Richard's suggestion below. Here's the log output:
SQLITE ERROR: (28) attempt to open "/Users/xxx/Library/Developer/CoreSimulator/Devices/CF762060-7D23-4C79-A466-7F20AB6233E7/data/Containers/Data/Application/582E1ED0-81E0-4CC7-A6F6-DBEBC101BBE8/tmp/etilqs_1ghbf1MSTa8ilSj" as
SQLITE ERROR: (14) cannot open file at line 30595 of [f66f7a17b7]
SQLITE ERROR: (14) os_unix.c:30595: (17) open(/Users/xxx/Library/Developer/CoreSimulator/Devices/CF762060-7D23-4C79-A466-7F20AB6233E7/data/Containers/Data/Application/582E1ED0-81E0-4CC7-A6F6-DBEBC101BBE8/tmp/etilqs_1ghbf1MST

Answer 1

I've noticed that even a :memory: database will files on disk if you create a temporary table. The temporary files for unix system are built by a Prng, so there is a non-zero chance of name collision if lots and lots of temporary files are created simultaneously. Or, if the disk is full, the create could fail. Or if for some reason the unix temp directory is not accessible either because it's been deleted or permissions on it are invalid.
For example, I've turned on several loggers in sqlite3 command line by adding these command line arguments to llvc-gcc: -DSQLITE_DEBUG_OS_TRACE=1 -DSQLITE_TEST=1 -DSQLITE_DEBUG=1 then I observed a temp file being created from the command line using this SQL:
$ ./sqlite3
SQLite version 3.8.8.2 2015-01-30 14:30:45
Enter ".help" for usage hints.
Connected to a transient in-memory database.
Use ".open FILENAME" to reopen on a persistent database.
sqlite> create temporary table t( x );
OPENX 3 /var/folders/nf/l1cw8sn1707b73zy5nqycrpw0000gn/T//etilqs_fvwR6KbMm518S4w 01002
OPEN 3
WRITE 3 512 0 0
OPENX 4 /var/folders/nf/l1cw8sn1707b73zy5nqycrpw0000gn/T//etilqs_OJJJ1lrTtQIFnUO 05402
OPEN 4
WRITE 4 1024 0 0
WRITE 4 1024 1024 0
WRITE 3 28 0 0
sqlite>

Answer 2

No ideas. But perhaps if you turned on the error and warning log it will give some clues.