Given the disparate processes needing access, and that you need read and write access. If you have the memory to maintain 300MB in RAM, then a ramdisc is by far your easiest and sanest option.

Ram discs have minimal overhead, and the only change required by the applications would be for the paths to change. Even that could be eliminated if you can use a symbolic link. The only downside is the risk of data loss in the event that the server crashes.

There are several ways that you could approach mitigating the data loss, some simplistic, other quite involved depending on the level of reliablility to you need.

An interesting thought, but I emphasis its nothing more than a thought, would be to create a partition/filesystem on disc the same size as the ram disc, and use mirroring to reflect the ramdisc onto the filesystem. Whether there is any mileage in the idea depends on which os, mirroring software etc and whether the latter can be configured to use a ram disk.

Attempting to use any form of caching is likely to be a problem as caching only really benefits you if the same sections of the data are being repeatedly accessed. Given all the different processes that would be vying for cache space in your scenario, your likely to slow things down with cache thrash rather than speed them up.