File header cache size

[Wim Van den Wyngaert]

Back on 5000.

Did a dir in a loop : also 100% (for 100 files).

Did 2 different dir in a loop : also 100% (200 files).

Did 2 dir of 10 directories each in a loop : 100% (2000 files)

Did 2 dir of 11.000 files each : 0%.

Reduced number of files to 3800. Dir in a loop : 100%. BTW : with cache 5 times faster.

Increased to 5700 files. Again 0%.

As soon as the number of files is bigger than the cache the cache isn't used ?

Wim

[Wim Van den Wyngaert]

It's probably FIFO. So, with 5000+ you simply create overhead of updating the cache but almost never benefit from it.

[Volker Halle · Accepted solution]

Wim,


BTW : with cache 5 times faster.


If you have a 100% hit rate from the File HDR cache, your CPU becomes the bottleneck, as all the headers are found in the cache and no disk IO is needed.

The buffer replacement algorithm for the buffer pools #0, #1 and #2 is: LRU = Leat Recently Used.

So yes, if the no. of files exceeds the no. of cache buffers, the file header cache won't help at all.

You can also flush the cache explicitly by e.g. using SET VOL/REBUILD disk

Volker.

[Wim Van den Wyngaert]

Case closed.

BTW : ana/sys display the % incorrect in clue mem/stat. Autogen however does it correctly.

Thanks Volker. Your the best.

Wim