• Brad Fitzpatrick's avatar
    database/sql: fix driver Conn refcounting with prepared statements · 277047f5
    Brad Fitzpatrick authored
    The refcounting of driver Conns was completedly busted and
    would leak (be held open forever) with any reasonable
    load. This was a significant regression from Go 1.0.
    
    The core of this patch is removing one line:
    
         s.db.addDep(dc, s)
    
    A database conn (dc) is a resource that be re-created any time
    (but cached for speed) should not be held open forever with a
    dependency refcount just because the Stmt (s) is alive (which
    typically last for long periods of time, like forever).
    
    The meat of the patch is new tests. In fixing the real issue,
    a lot of tests then failed due to the fakedb_test.go's paranoia
    about closing a fakeConn while it has open fakeStmts on it. I
    could've ignored that, but that's been a problem in the past for
    other bugs.
    
    Instead, I now track per-Conn open statements and close them
    when the the conn closes.  The proper way to do this would've
    been making *driverStmt a finalCloser and using the dep mechanism,
    but it was much more invasive. Added a TODO instead.
    
    I'd like to give a way for drivers to opt-out of caring about
    driver.Stmt closes before a driver.Conn close, but that's a TODO
    for the future, and that TODO is added in this CL.
    
    I know this is very late for Go 1.1, but database/sql is
    currently nearly useless without this.
    
    I'd like to believe all these database/sql bugs in the past
    release cycle are the result of increased usage, number of
    drivers, and good feedback from increasingly-capable Go
    developers, and not the result of me sucking.  It's also hard
    with all the real drivers being out-of-tree, so I'm having to
    add more and more hooks to fakedb_test.go to simulate things
    which real drivers end up doing.
    
    Fixes #5323
    
    R=golang-dev, snaury, gwenn.kahz, google, r
    CC=golang-dev
    https://golang.org/cl/8836045
    277047f5
sql_test.go 26.3 KB