Author: adrian.chadd
Date: Sun May 17 08:03:01 2009
New Revision: 14050
Modified:
wiki/PageName.wiki
Log:
Edited wiki page through web user interface.
Modified: wiki/PageName.wiki
==============================================================================
--- wiki/PageName.wiki (original)
+++ wiki/PageName.wiki Sun May 17 08:03:01 2009
@@ -12,6 +12,12 @@
= Overload during storeCreate =
+The two selection algorithms, "round robin" and "least load", both check
to make sure the storedir is OK (load < 1000 and > 0). Storedirs which are
not OK for this object are skipped by the selection logic.
+
= Overload during read / write IO =
+The storage logic does not currently handle temporary IO overloading - the
IO must complete or error, aborting the swapin/swapout. The storage modules
will generally call some "sync" function to complete some pending IO before
completing the current IO.
+
= Problems with the load handling =
+
+The load handling was written for a forward proxy load where it was OK to
occasionally miss an object. Reverse proxy loads with highly popular
objects can confuse the above logic. In particular, a frequently requested
object (say, a large one with range requests) seems to be evicted from the
cache following a transient high load spike and this overloads the backends
with range requests.
\ No newline at end of file
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