Mesa has supported on-disk shader cache for years to help speed-up game load times and overall system efficiencies. They had shifted from a multi-file cache layout to a single file cache for greater space savings . Steam also added support for the single-file cache . But now upstream Mesa is shifting back from the single-file cache default to the multi-file cache over performance issues.

Dmitry Osipenko made the change to re-enable the multi-file cache by default. The multi-file cache causes greater disk usage than the single-file cache, but performance issues have been coming up when the single-file cache is rather full.

The MESA_DISK_CACHE_DATABASE=1 can be ised to activate the Mesa-DB single file on-disk shader cache for those preferring it, but the default is back with the multi-file cache layout.

In the merge request now merged to Mesa Git it's summed up as:

"Over past months a performance issue was found with the Mesa-DB cache implementation that results in a too slow cache startup time when cache is full. A better indexing strategy will need to be invented to mitigate the issue. Until then, let's default back to the multi-file cache."

So for now, back with the multi-file cache which is still better than no cache at all.