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id ▼ node_id number title user state locked assignee milestone comments created_at updated_at closed_at author_association pull_request body repo type active_lock_reason performed_via_github_app reactions draft state_reason
751195017 MDU6SXNzdWU3NTExOTUwMTc= 1111 Accessing a database's `.json` is slow for very large SQLite files asg017 15178711 open 0     3 2020-11-26T00:27:27Z 2021-01-04T19:57:53Z   CONTRIBUTOR   I have a SQLite DB that's pretty large, 23GB and something like 300 million rows. I expect that most queries I run on it will be slow, which is fine, but there are some things that Datasette does that makes working with the DB very slow. Specifically, when I access the `.json` metadata for a table (which I believe it comes from `datasette/views/database.py`, it takes 43 seconds for the request to come in: ```bash $ time curl localhost:9999/out.json {"database": "out", "size": 24291454976, "tables": [{"name": "PageviewsHour", "columns": ["file", "code", "page", "pageviews"], "primary_keys": [], "count": null, "hidden": false, "fts_table": null, "foreign_keys": {"incoming": [], "outgoing": [{"other_table": "PageviewsHourFiles", "column": "file", "other_column": "file_id"}]}, "private": false}, {"name": "PageviewsHourFiles", "columns": ["file_id", "filename", "sha256", "size", "day", "hour"], "primary_keys": ["file_id"], "count": null, "hidden": false, "fts_table": null, "foreign_keys": {"incoming": [{"other_table": "PageviewsHour", "column": "file_id", "other_column": "file"}], "outgoing": []}, "private": false}, {"name": "sqlite_sequence", "columns": ["name", "seq"], "primary_keys": [], "count": 1, "hidden": false, "fts_table": null, "foreign_keys": {"incoming": [], "outgoing": []}, "private": false}], "hidden_count": 0, "views": [], "queries": [], "private": false, "allow_execute_sql": true, "query_ms": 43340.23213386536} real 0m43.417s user 0m0.006s sys 0m0.016s ``` I suspect this is because a `COUNT(*)` is happening under the hood, which, when I run it through sqlite directly, does take around the same time: ```bash $ time sqlite3 out.db < <(echo "select count(*) from PageviewsHour;") 362794272 real 0m44.523s user 0m2.497s sys 0m6.703s ``` I'm using the `.json` request in the [Observable Datasette Client](https://observablehq.com/@asg017/datasette-client) to 1) verify that a link passed in is a reachable Datasette instance, and 2) a quick way to look at metadata for a db. A few differe… datasette 107914493 issue     {"url": "https://api.github.com/repos/simonw/datasette/issues/1111/reactions", "total_count": 0, "+1": 0, "-1": 0, "laugh": 0, "hooray": 0, "confused": 0, "heart": 0, "rocket": 0, "eyes": 0}    

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