On Mon, Feb 07, 2011 at 10:55:47AM -0500, Mark Phippard wrote: > On Mon, Feb 7, 2011 at 10:52 AM, Stefan Sperling <s...@elego.de> wrote: > > > Where is the temporary table stored? Is it back by a file or memory? > > If backed by memory, do we have to worry about memory consumption for > > large working copies? > > The patch says it is backed by a file.
Yes, it does say that in a comment but I didn't see where this is being enforced in the code. Checking the sqlite docs gave the answer: "When the name of the database file handed to sqlite3_open() or to ATTACH is an empty string, then a new temporary file is created to hold the database." http://sqlite.org/inmemorydb.html This is what the patch does: +-- STMT_ATTACH_TEMPORARY_DATABASE +ATTACH DATABASE '' AS temp_query_cache; And note that the sqlite docs also say: "Even though a disk file is allocated for each temporary database, in practice the temporary database usually resides in the in-memory pager cache and hence is very little difference between a pure in-memory database created by ":memory:" and a temporary database created by an empty filename. The sole difference is that a ":memory:" database must remain in memory at all times whereas parts of a temporary database might be flushed to disk if database becomes large or if SQLite comes under memory pressure." Neat :)
