Question

I am running into an issue with a sqlite database program. I am trying to attach 30 databases together and running into a limit of 10 error:
“SQLite error
too many attached databases – max 10”

According to http://www.sqlite.org/c3ref/limit.html we should be able to set the max number of allowed attached databases to more than 10. I am using C# and system.data.sqlite.dll for the interface. Does anyone know how I could set the limit > 10?

Answer 1

From the implementation limits page (emphasis mine):

The maximum number of attached databases can be lowered at run-time using the sqlite3_limit(db,SQLITE_LIMIT_ATTACHED,size) interface.

From the Run-time limits page:

For each limit category SQLITE_LIMIT_NAME there is a hard upper bound set at compile-time by a C preprocessor macro called SQLITE_MAX_NAME. (The _ LIMIT _ in the name is changed to _ MAX _.) Attempts to increase a limit above its hard upper bound are silently truncated to the hard upper bound.

Based on the fact that you can only lower the limit, I think the SQLITE_LIMIT_ATTACHED is a compiled constant set to 10. If you want to make it larger, you’ll have to change it in source code and recompile SQLite.

And there’s more:

The code generator in SQLite uses bitmaps to keep track of attached databases. That means that the number of attached databases cannot be increased above 62.

There you have it. Even if you make it larger than 10, 62 is a physical hard limit due to the architecture of the database.