How does BerkeleyDB know when cached results from stat function are valid ?

Question

Something curious: I have a berkeley database about 2G in size and a program that (1) opens the database, not DB_RDONLY; (2) calls stat(), without DB_FAST_STAT; (3) calls sync(); (4) calls close().
Running this program the first time takes a good amount of time in the stat() function - 20 minutes at least - and thrashes the disk all that time. So it's trawling the database to get record counts etc.
Running the program again takes only a few seconds so clearly the database is caching those stats and knows they're up to date - makes sense.
What's odd though is why the stats weren't known to be up to date on the first run. The database was actually copied from another box where the last thing to happen was a run of the same program. So it should have had up-to-date stats cached in it.
It's as if the cached values are somehow invalidated by moving the database to another machine. Why would that happen ? Where are the cached stats held and how does berekelyDB decide when they're up to date ?

Answer 1

I still cannot solve this problem, but I have some more observations:
1) yes it is a JApplet, and yes, the data streaming is performed in a separate thread.
2) Wireshark sniffing shows that data sent out by the PHP datasource on the server is sent immediately, and is not buffered (am using ob_start(), ob_flush() and flush() alls in the PHP script).
3) On Windows Vista, using Internet Explorer or Firefox, there is a constant 30 second delay before the Applet returns from this line: InputStream is = url.openStream();
4) After this 30 seconds, data appears in the Applet, but it can be seen also with java console debug prints that the data seems to be buffered. The newest data shown in the Applet is not the newest data sent to the client by the PHP datasource script.
5) On a SUSE Linux client, the Applet works as it should, there is no delay time in showing the data.
It appears as if there is on Windows a buffering of data which I do not wish to have and which does not occur on Linux. I need to find out how to get the URL openStream() call to return immediately allowing the initial data to be read and shown on the Applet. And I need to remove the buffering of data so that the data can be shown on the Applet when it arrives.
Can anyone help? Why does this work on Linux but not on Windows, and what can I do, at best within the Java code, to get the Applet to work on Windows as it does on Linux?
Thanks!
Steve, Denmark