This session covers introduction to self-heal daemon for replication, and the types of crawls self-heal daemon does to make sure the volume is always replicated in cases of failures. Code walk through of the necessary functions that do both index and full crawl are covered in detail.

1. Glusterfs Session #16
Self-heal daemon ( for replication)
ravishankar.n@pavilion.io

2. Agenda
- Intro to self-heal daemon (shd)
- Types of crawl in shd
- Code walkthrough

3. Intro to self-heal daemon (shd)
- What is it and why do we need it?
client-side heal (vs) shd heal
- Who manages it
root 10181 0.0 0.0 794532 8820 ? Ssl 20:10 0:00 /usr/local/sbin/
glusterfs -s localhost --volfile-id shd/testvol
-p /var/run/
gluster/shd/testvol/testvol-shd.pid -l /var/log/
glusterfs/glustershd.log -S /var/run/
gluster/1a8a981fe17db38b.socket
--xlator-option *replicate*.node-uuid=719e5dd8-f770-43ba-b924-817bcfc0ed06 --process-name
glustershd --client-pid=-6
- basically a client process (see volfile - has cluster/afr and protocol/client xlators)
- Managed by glusterd
xlators/mgmt/glusterd/src/glusterd-volgen.c
xlators/mgmt/glusterd/src/glusterd-shd-svc*
- controlled via CLI : gluster volume heal $VOLNAME {enable|disable}

4. Types of crawl in shd
- What is crawling?
- Scan through $LOCATION, identify what needs heal, and do the heal.
1. Full sweep / heal
LOCATION = full filesystem
gluster volume heal $VOLNAME full
2. Index sweep / heal
LOCATION = .glusterfs/indices/{dirty, xattrop, entry-changes/*}
Manual: gluster volume heal $VOLNAME (or)
Automatic: Once in every $heal-timeout seconds:
gluster volume set $VOLNAME cluster.heal-timeout $heal-timeout

5. Code walkthrough
~/workspace/glusterfs$ ls xlators/cluster/afr/src/afr-self-heal*
xlators/cluster/afr/src/afr-self-heald.c
xlators/cluster/afr/src/afr-self-heald.h
xlators/cluster/afr/src/afr-self-heal.h
xlators/cluster/afr/src/afr-self-heal-common.c
xlators/cluster/afr/src/afr-self-heal-metadata.c
xlators/cluster/afr/src/afr-self-heal-name.c
xlators/cluster/afr/src/afr-self-heal-data.c
xlators/cluster/afr/src/afr-self-heal-entry.c

6. Functions/ variables
client-side heal:
afr_throttled_selfheal(),background-self-heal-count, heal-wait-queue-length, afr_selfheal()
shd heal:
Manually via CLI:
afr_notify()-->afr_xl_op() --> afr_shd_index_healer_spawn() / afr_shd_full_healer_spawn()
Automatic periodic crawl:
afr_notify()->afr_selfheal_childup()-->afr_shd_index_healer_spawn()
struct afr_self_heald_t, struct subvol_healer