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authorJeff Darcy <jdarcy@redhat.com>2012-03-12 09:32:40 -0400
committerAnand Avati <avati@redhat.com>2012-05-31 17:29:01 -0700
commitddc044bfa2840981de4003c3b9efcac84387dc2b (patch)
treea83d476702cac7ecc7ae59057c368f622a51af4c /xlators/cluster/afr/src/afr-self-heal.h
parente066a5fea7bdaa5da78e49c9a5bf344af2f33d3c (diff)
replicate: add hashed read-child method.
Both the first-to-respond method and the round-robin method are susceptible to clients repeatedly choosing the same servers across a series of opens, creating hot spots. Also, the code to handle a replica being down will ignore both methods and just choose the first remaining (which is not an issue for two-way but can be otherwise). The hashed method more reliably avoids such hot spots. There are three values/modes. 0: use the old (broken) methods. 1: select a read-child based on a hash of the file's GFID, so all clients will choose the same subvolume for a file (ensuring maximum consistency) but will distribute load for a set of files. 2: select a read-child based on a hash of the file's GFID plus the client's PID, so different children will distribute load even for one file. Mode 2 will probably be optimal for most cases. Using response time when we open the file is problematic, both because a single sample might not have been representative even then and because load might have shifted in the hours or days since (for long-lived files). Trying to use more current load information can lead to "herd following" behavior which is just as bad. Pseudo-random distribution is likely to be the best we can reasonably do, just as it is for DHT. Change-Id: I798c2760411eacf32e82a85f03bb7b08a4a49461 BUG: 802513 Signed-off-by: Jeff Darcy <jdarcy@redhat.com> Reviewed-on: http://review.gluster.com/2926 Tested-by: Gluster Build System <jenkins@build.gluster.com> Reviewed-by: Anand Avati <avati@redhat.com>
Diffstat (limited to 'xlators/cluster/afr/src/afr-self-heal.h')
-rw-r--r--xlators/cluster/afr/src/afr-self-heal.h3
1 files changed, 2 insertions, 1 deletions
diff --git a/xlators/cluster/afr/src/afr-self-heal.h b/xlators/cluster/afr/src/afr-self-heal.h
index 627a2115a..2efc1116d 100644
--- a/xlators/cluster/afr/src/afr-self-heal.h
+++ b/xlators/cluster/afr/src/afr-self-heal.h
@@ -45,5 +45,6 @@ afr_self_heal (call_frame_t *frame, xlator_t *this, inode_t *inode);
int
afr_lookup_select_read_child_by_txn_type (xlator_t *this, afr_local_t *local,
dict_t **xattr,
- afr_transaction_type txn_type);
+ afr_transaction_type txn_type,
+ uuid_t gfid);
#endif /* __AFR_SELF_HEAL_H__ */