[Cartoweb-dev] [Bug 1318] New: Caching issue: under heavy load, a cache entry may be computed several times

[bugzilla-daemon at bugzilla.maptools.org]

http://bugzilla.maptools.org/show_bug.cgi?id=1318

           Summary: Caching issue: under heavy load, a cache entry may be
                    computed several times
           Product: CartoWeb
           Version: unspecified
          Platform: PC
        OS/Version: Linux
            Status: NEW
          Severity: enhancement
          Priority: P2
         Component: Core
        AssignedTo: cartoweb-dev at lists.maptools.org
        ReportedBy: sylvain.pasche at camptocamp.com


What happens actually is the following:

1 Client makes request
2 Server sees it needs to cache request
3 Mapserver is called to generate the map
4 The map is put in the cache.

There is a small window during which a request may be put twice in the cache:
with client A and B:

A 1 make request
A 2 Server sees it needs to cache request
B 1 Client makes request
B 2 Server sees it needs to cache request
A 3 Mapserver is called to generate the map
A 4 The map is put in the cache.
B 3 Mapserver is called to generate the map
B 4 The map is put in the cache.

A 4 The map is put in the cache.
B 4 The map is put in the cache.

This is not a problem, because the cache writing operation is atomic. However,
the enhancement would be to block client B which A is caching the result, so
that it can reply with a cached result instead of computing it again.



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