(6410) SQLITE_IOERR_GETTEMPPATH thrown on first write on Android

[grigoryk]

For reference: The SQLITE_IOERR_GETTEMPPATH error code is an extended error code for SQLITE_IOERR indicating that the VFS is unable to determine a suitable directory in which to place temporary files.

This implies that SQLite being used is compiled with SQLITE_TEMP_STORE=1 build flag, and somehow in this particular environment it's failing to determine a suitable location on disk for temp files.

From Firefox's build config, on Android SQLite is forced to use memory for temp store: https://dxr.mozilla.org/mozilla-central/source/db/sqlite3/src/moz.build#90 "On Android there's no tmp partition, so always use a MEMORY temp store" - via SQLITE_TEMP_STORE=3 flag.

We can force temp files to be stored in memory via PRAGMA temp_store=2.

[grigoryk]

Following Firefox's config, it's using memory store on Android (no other choice) and on 64bit platforms.

Try to use a MEMORY temp store when possible. That allows for better performance and doesn't suffer from a full separate tmp partition. Exclude 32bit platforms due to address space fragmentation issues.

Proposed patch in #506 forces memory storage indiscriminately. Ideally I'd like to follow what Firefox is doing and exclude 32bit platforms, but I'm not sure how to actually achieve that.

@ncalexan , thoughts?

[ncalexan]

The linked code isn't testing for 32-bit on Android at all. For reference, from https://sqlite.org/tempfiles.html:

The SQLITE_TEMP_STORE compile-time parameter is a #define whose value is an integer between 0 and 3, inclusive. The meaning of the SQLITE_TEMP_STORE compile-time parameter is as follows:

0. Temporary files are always stored on disk regardless of the setting of the temp_store pragma.
1. Temporary files are stored on disk by default but this can be overridden by the temp_store pragma.
2. Temporary files are stored in memory by default but this can be overridden by the temp_store pragma.
3. Temporary files are always stored in memory regardless of the setting of the temp_store pragma.

I think we should go with 2 everywhere for Mentat: default to memory, let consumers override.

[rnewman]

I'm happy defaulting to memory storage for now (#506), but keeping this issue open to alter our SQLite build options or provide a configuration parameter: when used with Firefox's SQLite we'll get the former for free, and #506 doesn't allow consumers to override.