----- Original Message ----- > From: "Raghavendra Gowdappa" <rgowdapp@xxxxxxxxxx> > To: "Gluster Devel" <gluster-devel@xxxxxxxxxxx>, "gluster-users" <gluster-users@xxxxxxxxxxx> > Sent: Tuesday, November 8, 2016 10:37:56 AM > Subject: Feedback on DHT option "cluster.readdir-optimize" > > Hi all, > > We have an option in called "cluster.readdir-optimize" which alters the > behavior of readdirp in DHT. This value affects how storage/posix treats > dentries corresponding to directories (not for files). > > When this value is on, > * DHT asks only one subvol/brick to return dentries corresponding to > directories. > * Other subvols/bricks filter dentries corresponding to directories and send > only dentries corresponding to files. > > When this value is off (this is the default value), > * All subvols return all dentries stored on them. IOW, bricks don't filter > any dentries. > * Since a directory has one dentry representing it on each subvol, dht > (loaded on client) picks up dentry only from hashed subvol. > > Note that irrespective of value of this option, _all_ subvols return dentries > corresponding to files which are stored on them. > > This option was introduced to boost performance of readdir as (when set on), > filtering of dentries happens on bricks and hence there is reduced: > 1. network traffic (with filtering all the redundant dentry information) > 2. number of readdir calls between client and server for the same number of > dentries returned to application (If filtering happens on client, lesser > number of dentries in result and hence more number of readdir calls. IOW, > result buffer is not filled to maximum capacity). > > We want to hear from you Whether you've used this option and if yes, > 1. Did it really boost readdir performance? > 2. Do you've any performance data to find out what was the percentage of > improvement (or deterioration)? > 3. Data set you had (Number of files, directories and organisation of > directories). 4. Volume information. IOW, how many subvols did dht had? > > If we find out that this option is really helping you, we can spend our > energies on fixing issues that will arise when this option is set to on. One > common issue with turning this option on is that when this option is set, > some directories might not show up in directory listing [1]. The reason for > this is that: > 1. If a directory can be created on a hashed subvol, mkdir (result to > application) will be successful, irrespective of result of mkdir on rest of > the subvols. > 2. So, any subvol we pick to give us dentries corresponding to directory need > not contain all the directories and we might miss out those directories in > listing. > > Your feedback is important for us and will help us to prioritize and improve > things. > > [1] https://www.gluster.org/pipermail/gluster-users/2016-October/028703.html > > regards, > Raghavendra _______________________________________________ Gluster-devel mailing list Gluster-devel@xxxxxxxxxxx http://www.gluster.org/mailman/listinfo/gluster-devel
