CephFS HDFS clients failing to respond to cache pressure about cephfs-hadoop HOT 3 OPEN

Yeah, the cache pressure messages frequently enough just mean that the client has so many files held open that it can't give up any when the MDS asks. I'm not sure if the HDFS shim is more (unnecessarily) prone to that than other interfaces or not.

from cephfs-hadoop.

Hi @hellertime the cephfs-hadoop shim is a thin layer over the cephfs userspace client (that in turn is the basis for the fuse client) so it probably isn't the shim itself that is causing this issue, although hadoop can be fairly brutal with leaving file handles open.

Have you tried this in Jewel? @gregsfortytwo @jcsp thoughts?

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@hellertime I haven't used spark on the hadoop-shim, but in the past I found with a little poking around in hadoop or a hadoop application I could find some dangling open file descriptors. one way to do this is to collect a client log and then look for files that accumulate opens without closes which can narrow down the parts of the hadoop application that have the open files.

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