IE Cache Corruption Problem and Solution (sort of)
Bernard
After a new window is opened via script with window.open(),
the following problem occurs in sessions of the majority
(more than 70%) of Internet Explorer 5 and 5.5 6.0 users:
The browser performs always conditional (resulting in code 304) and
sometimes unconditional GET requests to the server for files that were
retrieved from the browser cache successfully during the SAME browser
session.
The cache remains corrupted:
1) in the new window even if the files are requested
again in the new window multiple times.
2a) in the opener window after the new window is opened
2b) in the opener window after the new window is closed
Especially the performance of mouseover image swapping is affected
badly because the images are not shown before the response from the
server even for code 304 ("not modified") is received.
The "pre-loading" of images does not perform as expected for users who
use dial-up connections.
This applies to any pages that are either loaded into new windows or
open new windows themselves (e.g. pop-ups).
The cache settings "automatic" or "Every time you start Internet
Explorer"
(default) in the IE options do not fix this problem.
It appears that all versions of Windows including Windows 2000 are
affected
but only where the "Active Desktop" option has been installed.
Disabling the "Active Desktop" after installation does not fix
the problem as one might expect.
The above observations are backed up by overwhelming web site access
log statistics and multiple browser installations on test systems.
In contrast, the caches of the Netscape 3 and 4 browsers (used as
reference
in performance tests) always behave as expected.
The best possible workaround in scripting appears to be to disable
mouseover events depending on client side elapse time measurements
(loading from cache is in contrast almost instant) and disable event
procedures with a boolean flag accordingly.
That way, without browser detection code, "Active Desktop" IE users
will not be annoyed by delayed mouseover images and Netscape users and
the few smart IE users who did not install the "Active Desktop" will
see normal image swapping.
Bernard