issues: 688670158
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| 688670158 | MDU6SXNzdWU2ODg2NzAxNTg= | 147 | SQLITE_MAX_VARS maybe hard-coded too low | 96218 | open | 0 | 7 | 2020-08-30T07:26:45Z | 2021-02-15T21:27:55Z | CONTRIBUTOR | I came across this while about to open an issue and PR against the documentation for `batch_size`, which is a bit incomplete. As mentioned in #145, while: > [`SQLITE_MAX_VARIABLE_NUMBER`](https://www.sqlite.org/limits.html#max_variable_number) ... defaults to 999 for SQLite versions prior to 3.32.0 (2020-05-22) or 32766 for SQLite versions after 3.32.0. it is common that it is increased at compile time. Debian-based systems, for example, seem to ship with a version of sqlite compiled with SQLITE_MAX_VARIABLE_NUMBER set to 250,000, and I believe this is the case for homebrew installations too. In working to understand what `batch_size` was actually doing and why, I realized that by setting `SQLITE_MAX_VARS` in `db.py` to match the value my sqlite was compiled with (I'm on Debian), I was able to decrease the time to `insert_all()` my test data set (~128k records across 7 tables) from ~26.5s to ~3.5s. Given that this about .05% of my total dataset, this is time I am keen to save... Unfortunately, it seems that `sqlite3` in the python standard library doesn't expose the `get_limit()` C API (even though `pysqlite` used to), so it's hard to know what value sqlite has been compiled with (note that this could mean, I suppose, that it's less than 999, and even hardcoding `SQLITE_MAX_VARS` to the conservative default might not be adequate. It can also be lowered -- but not raised -- at runtime). The best I could come up with is `echo "" | sqlite3 -cmd ".limits variable_number"` (only available in `sqlite >= 2015-05-07 (3.8.10)`). Obviously this couldn't be relied upon in `sqlite_utils`, but I wonder what your opinion would be about exposing `SQLITE_MAX_VARS` as a user-configurable parameter (with suitable "here be dragons" warnings)? I'm going to go ahead and monkey-patch it for my purposes in any event, but it seems like it might be worth considering. | 140912432 | issue | {"url": "https://api.github.com/repos/simonw/sqlite-utils/issues/147/reactions", "total_count": 0, "+1": 0, "-1": 0, "laugh": 0, "hooray": 0, "confused": 0, "heart": 0, "rocket": 0, "eyes": 0} |