html_url,issue_url,id,node_id,user,created_at,updated_at,author_association,body,reactions,issue,performed_via_github_app
https://github.com/simonw/datasette/issues/283#issuecomment-781670827,https://api.github.com/repos/simonw/datasette/issues/283,781670827,MDEyOklzc3VlQ29tbWVudDc4MTY3MDgyNw==,9599,2021-02-18T22:16:46Z,2021-02-18T22:16:46Z,OWNER,"Demo is now live here: https://latest.datasette.io/_memory

The documentation is at https://docs.datasette.io/en/latest/sql_queries.html#cross-database-queries - it links to this example query: https://latest.datasette.io/_memory?sql=select%0D%0A++%27fixtures%27+as+database%2C+*%0D%0Afrom%0D%0A++%5Bfixtures%5D.sqlite_master%0D%0Aunion%0D%0Aselect%0D%0A++%27extra_database%27+as+database%2C+*%0D%0Afrom%0D%0A++%5Bextra_database%5D.sqlite_master","{""total_count"": 0, ""+1"": 0, ""-1"": 0, ""laugh"": 0, ""hooray"": 0, ""confused"": 0, ""heart"": 0, ""rocket"": 0, ""eyes"": 0}",325958506,
https://github.com/simonw/datasette/issues/283#issuecomment-781665560,https://api.github.com/repos/simonw/datasette/issues/283,781665560,MDEyOklzc3VlQ29tbWVudDc4MTY2NTU2MA==,9599,2021-02-18T22:06:14Z,2021-02-18T22:06:14Z,OWNER,"The implementation in #1232 is ready to land. It's the simplest-thing-that-could-possibly-work: you can run `datasette one.db two.db three.db --crossdb` and then use the `/_memory` page to run joins across tables from multiple databases.

It only works on the first 10 databases that were passed to the command-line. This means that if you have a Datasette instance with hundreds of attached databases (see [Datasette Library](https://github.com/simonw/datasette/issues/417)) this won't be particularly useful for you.

So... a better, future version of this feature would be one that lets you join across databases on command - maybe by hitting `/_memory?attach=db1&attach=db2` to get a special connection.

Also worth noting: plugins that implement the [prepare_connection()](https://docs.datasette.io/en/stable/plugin_hooks.html#prepare-connection-conn-database-datasette) hook can attach additional databases - so if you need better, customized support for this one way to handle that would be with a custom plugin.","{""total_count"": 0, ""+1"": 0, ""-1"": 0, ""laugh"": 0, ""hooray"": 0, ""confused"": 0, ""heart"": 0, ""rocket"": 0, ""eyes"": 0}",325958506,
https://github.com/simonw/datasette/pull/1232#issuecomment-781651283,https://api.github.com/repos/simonw/datasette/issues/1232,781651283,MDEyOklzc3VlQ29tbWVudDc4MTY1MTI4Mw==,9599,2021-02-18T21:37:55Z,2021-02-18T21:37:55Z,OWNER,"UI listing the attached tables:

<img width=""888"" alt=""_memory"" src=""https://user-images.githubusercontent.com/9599/108424809-8015ce80-71ee-11eb-8752-03c459f89320.png"">
","{""total_count"": 0, ""+1"": 0, ""-1"": 0, ""laugh"": 0, ""hooray"": 0, ""confused"": 0, ""heart"": 0, ""rocket"": 0, ""eyes"": 0}",811407131,
https://github.com/simonw/datasette/pull/1232#issuecomment-781641728,https://api.github.com/repos/simonw/datasette/issues/1232,781641728,MDEyOklzc3VlQ29tbWVudDc4MTY0MTcyOA==,9599,2021-02-18T21:19:34Z,2021-02-18T21:19:34Z,OWNER,"I tested the demo deployment like this:
```
datasette publish cloudrun fixtures.db extra_database.db \                                      
            -m fixtures.json \
            --plugins-dir=plugins \
            --branch=crossdb \
            --extra-options=""--setting template_debug 1 --crossdb"" \
            --install=pysqlite3-binary \
            --service=datasette-latest-crossdb
```","{""total_count"": 0, ""+1"": 0, ""-1"": 0, ""laugh"": 0, ""hooray"": 0, ""confused"": 0, ""heart"": 0, ""rocket"": 0, ""eyes"": 0}",811407131,
https://github.com/simonw/datasette/pull/1232#issuecomment-781637292,https://api.github.com/repos/simonw/datasette/issues/1232,781637292,MDEyOklzc3VlQ29tbWVudDc4MTYzNzI5Mg==,9599,2021-02-18T21:11:31Z,2021-02-18T21:11:31Z,OWNER,Due to bug #1233 I'm going to publish the additional database as `extra_database.db` rather than `extra database.db` as it is used in the tests.,"{""total_count"": 0, ""+1"": 0, ""-1"": 0, ""laugh"": 0, ""hooray"": 0, ""confused"": 0, ""heart"": 0, ""rocket"": 0, ""eyes"": 0}",811407131,
https://github.com/simonw/datasette/issues/1233#issuecomment-781636590,https://api.github.com/repos/simonw/datasette/issues/1233,781636590,MDEyOklzc3VlQ29tbWVudDc4MTYzNjU5MA==,9599,2021-02-18T21:10:08Z,2021-02-18T21:10:08Z,OWNER,I think the bug is here: https://github.com/simonw/datasette/blob/640ac7071b73111ba4423812cd683756e0e1936b/datasette/utils/__init__.py#L349-L373,"{""total_count"": 0, ""+1"": 0, ""-1"": 0, ""laugh"": 0, ""hooray"": 0, ""confused"": 0, ""heart"": 0, ""rocket"": 0, ""eyes"": 0}",811458446,
https://github.com/simonw/datasette/pull/1232#issuecomment-781634819,https://api.github.com/repos/simonw/datasette/issues/1232,781634819,MDEyOklzc3VlQ29tbWVudDc4MTYzNDgxOQ==,9599,2021-02-18T21:06:43Z,2021-02-18T21:06:43Z,OWNER,I'll document this option on https://docs.datasette.io/en/stable/sql_queries.html,"{""total_count"": 0, ""+1"": 0, ""-1"": 0, ""laugh"": 0, ""hooray"": 0, ""confused"": 0, ""heart"": 0, ""rocket"": 0, ""eyes"": 0}",811407131,
https://github.com/simonw/datasette/pull/1232#issuecomment-781629841,https://api.github.com/repos/simonw/datasette/issues/1232,781629841,MDEyOklzc3VlQ29tbWVudDc4MTYyOTg0MQ==,9599,2021-02-18T20:57:23Z,2021-02-18T20:57:23Z,OWNER,"The new warning looks like this:

<img width=""514"" alt=""datasette_—_pipenv_shell_▸_Python_—_182×66"" src=""https://user-images.githubusercontent.com/9599/108420562-d41db480-71e8-11eb-87e3-1cddd65627c2.png"">
","{""total_count"": 0, ""+1"": 0, ""-1"": 0, ""laugh"": 0, ""hooray"": 0, ""confused"": 0, ""heart"": 0, ""rocket"": 0, ""eyes"": 0}",811407131,
https://github.com/simonw/datasette/pull/1232#issuecomment-781598585,https://api.github.com/repos/simonw/datasette/issues/1232,781598585,MDEyOklzc3VlQ29tbWVudDc4MTU5ODU4NQ==,9599,2021-02-18T19:57:30Z,2021-02-18T19:57:30Z,OWNER,It would also be neat if https://latest.datasette.io/ had multiple databases attached in order to demonstrate this feature.,"{""total_count"": 0, ""+1"": 0, ""-1"": 0, ""laugh"": 0, ""hooray"": 0, ""confused"": 0, ""heart"": 0, ""rocket"": 0, ""eyes"": 0}",811407131,
https://github.com/simonw/datasette/pull/1232#issuecomment-781594632,https://api.github.com/repos/simonw/datasette/issues/1232,781594632,MDEyOklzc3VlQ29tbWVudDc4MTU5NDYzMg==,9599,2021-02-18T19:50:21Z,2021-02-18T19:50:21Z,OWNER,"It would be neat if the `/_memory` page showed a list of attached databases, to indicate that the `--crossdb` option is working and give people links to click to start running queries.","{""total_count"": 0, ""+1"": 0, ""-1"": 0, ""laugh"": 0, ""hooray"": 0, ""confused"": 0, ""heart"": 0, ""rocket"": 0, ""eyes"": 0}",811407131,
https://github.com/simonw/datasette/issues/283#issuecomment-781593169,https://api.github.com/repos/simonw/datasette/issues/283,781593169,MDEyOklzc3VlQ29tbWVudDc4MTU5MzE2OQ==,9599,2021-02-18T19:47:34Z,2021-02-18T19:47:34Z,OWNER,"I have a working version now, moving development to a pull request.","{""total_count"": 0, ""+1"": 0, ""-1"": 0, ""laugh"": 0, ""hooray"": 0, ""confused"": 0, ""heart"": 0, ""rocket"": 0, ""eyes"": 0}",325958506,
https://github.com/simonw/datasette/issues/283#issuecomment-781591015,https://api.github.com/repos/simonw/datasette/issues/283,781591015,MDEyOklzc3VlQ29tbWVudDc4MTU5MTAxNQ==,9599,2021-02-18T19:44:02Z,2021-02-18T19:44:02Z,OWNER,For the moment I'm going to hard-code a `SQLITE_LIMIT_ATTACHED=10` constant and only attach the first 10 databases to the `_memory` connection.,"{""total_count"": 0, ""+1"": 0, ""-1"": 0, ""laugh"": 0, ""hooray"": 0, ""confused"": 0, ""heart"": 0, ""rocket"": 0, ""eyes"": 0}",325958506,
https://github.com/simonw/datasette/issues/283#issuecomment-781574786,https://api.github.com/repos/simonw/datasette/issues/283,781574786,MDEyOklzc3VlQ29tbWVudDc4MTU3NDc4Ng==,9599,2021-02-18T19:15:37Z,2021-02-18T19:15:37Z,OWNER,`select * from pragma_database_list();` is useful - shows all attached databases for the current connection.,"{""total_count"": 0, ""+1"": 0, ""-1"": 0, ""laugh"": 0, ""hooray"": 0, ""confused"": 0, ""heart"": 0, ""rocket"": 0, ""eyes"": 0}",325958506,
https://github.com/simonw/datasette/issues/283#issuecomment-781573676,https://api.github.com/repos/simonw/datasette/issues/283,781573676,MDEyOklzc3VlQ29tbWVudDc4MTU3MzY3Ng==,9599,2021-02-18T19:13:30Z,2021-02-18T19:13:30Z,OWNER,"It turns out SQLite defaults to a maximum of 10 attached databases. This can be increased using a compile-time constant, but even with that it cannot be more than 62: https://stackoverflow.com/questions/9845448/attach-limit-10","{""total_count"": 0, ""+1"": 0, ""-1"": 0, ""laugh"": 0, ""hooray"": 0, ""confused"": 0, ""heart"": 0, ""rocket"": 0, ""eyes"": 0}",325958506,
https://github.com/simonw/datasette/issues/1231#issuecomment-781560989,https://api.github.com/repos/simonw/datasette/issues/1231,781560989,MDEyOklzc3VlQ29tbWVudDc4MTU2MDk4OQ==,9599,2021-02-18T18:50:53Z,2021-02-18T18:50:53Z,OWNER,Ideally I'd figure out a way to replicate this error in a concurrent unit test.,"{""total_count"": 0, ""+1"": 0, ""-1"": 0, ""laugh"": 0, ""hooray"": 0, ""confused"": 0, ""heart"": 0, ""rocket"": 0, ""eyes"": 0}",811367257,
https://github.com/simonw/datasette/issues/1231#issuecomment-781560865,https://api.github.com/repos/simonw/datasette/issues/1231,781560865,MDEyOklzc3VlQ29tbWVudDc4MTU2MDg2NQ==,9599,2021-02-18T18:50:38Z,2021-02-18T18:50:38Z,OWNER,"I started trying to use locks to resolve this but I've not figured out the right way to do that yet - here's my first experiment:
```diff
diff --git a/datasette/app.py b/datasette/app.py
index 9e15a16..1681c9d 100644
--- a/datasette/app.py
+++ b/datasette/app.py
@@ -217,6 +217,7 @@ class Datasette:
         self.inspect_data = inspect_data
         self.immutables = set(immutables or [])
         self.databases = collections.OrderedDict()
+        self._refresh_schemas_lock = threading.Lock()
         if memory or not self.files:
             self.add_database(Database(self, is_memory=True), name=""_memory"")
         # memory_name is a random string so that each Datasette instance gets its own
@@ -324,6 +325,13 @@ class Datasette:
         self.client = DatasetteClient(self)
 
     async def refresh_schemas(self):
+        return
+        if self._refresh_schemas_lock.locked():
+            return
+        with self._refresh_schemas_lock:
+            await self._refresh_schemas()
+
+    async def _refresh_schemas(self):
         internal_db = self.databases[""_internal""]
         if not self.internal_db_created:
             await init_internal_db(internal_db)
```","{""total_count"": 0, ""+1"": 0, ""-1"": 0, ""laugh"": 0, ""hooray"": 0, ""confused"": 0, ""heart"": 0, ""rocket"": 0, ""eyes"": 0}",811367257,
https://github.com/simonw/datasette/issues/1226#issuecomment-781546512,https://api.github.com/repos/simonw/datasette/issues/1226,781546512,MDEyOklzc3VlQ29tbWVudDc4MTU0NjUxMg==,9599,2021-02-18T18:26:19Z,2021-02-18T18:26:19Z,OWNER,This broke CI: https://github.com/simonw/datasette/runs/1929355965?check_suite_focus=true,"{""total_count"": 0, ""+1"": 0, ""-1"": 0, ""laugh"": 0, ""hooray"": 0, ""confused"": 0, ""heart"": 0, ""rocket"": 0, ""eyes"": 0}",808843401,
https://github.com/simonw/datasette/issues/1226#issuecomment-781530157,https://api.github.com/repos/simonw/datasette/issues/1226,781530157,MDEyOklzc3VlQ29tbWVudDc4MTUzMDE1Nw==,9599,2021-02-18T18:00:15Z,2021-02-18T18:00:15Z,OWNER,"I can use `click.IntRange(min=None, max=None)` for this. https://click.palletsprojects.com/en/7.x/options/#ranges - inclusive on both edges.","{""total_count"": 0, ""+1"": 0, ""-1"": 0, ""laugh"": 0, ""hooray"": 0, ""confused"": 0, ""heart"": 0, ""rocket"": 0, ""eyes"": 0}",808843401,
https://github.com/simonw/datasette/issues/283#issuecomment-781077127,https://api.github.com/repos/simonw/datasette/issues/283,781077127,MDEyOklzc3VlQ29tbWVudDc4MTA3NzEyNw==,9599,2021-02-18T05:56:30Z,2021-02-18T05:57:34Z,OWNER,I'm going to to try prototyping the `--crossdb` option that causes `/_memory` to connect to all databases as a starting point and see how well that works.,"{""total_count"": 1, ""+1"": 0, ""-1"": 0, ""laugh"": 0, ""hooray"": 0, ""confused"": 0, ""heart"": 0, ""rocket"": 1, ""eyes"": 0}",325958506,