doc: How to generate and read statedump

Thanks to Poornima G's help with iobuf
Section explanation.

Change-Id: I17737fdbd1f402914f7e67fb4047f5c26ea5c36c
BUG: 1118309
Signed-off-by: Pranith Kumar K <pkarampu@redhat.com>
Reviewed-on: http://review.gluster.org/8288
Tested-by: Gluster Build System <jenkins@build.gluster.com>
Reviewed-by: Ravishankar N <ravishankar@redhat.com>
Reviewed-by: Krutika Dhananjay <kdhananj@redhat.com>
Reviewed-by: Humble Devassy Chirammal <humble.devassy@gmail.com>
Reviewed-by: Prashanth Pai <ppai@redhat.com>
Reviewed-by: Vijay Bellur <vbellur@redhat.com>

1 files changed, 318 insertions, 0 deletions

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+#Statedump
+Statedump is a file generated by glusterfs process with different data structure state which may contain the active inodes, fds, mempools, iobufs, memory allocation stats of different types of datastructures per xlator etc.
+
+##How to generate statedump
+We can find the directory where statedump files are created using 'gluster --print-statedumpdir' command.
+Create that directory if not already present based on the type of installation.
+Lets call this directory `statedump-directory`.
+
+We can generate statedump using 'kill -USR1 <pid-of-gluster-process>'.
+gluster-process is nothing but glusterd/glusterfs/glusterfsd process.
+
+There are also commands to generate statedumps for brick processes/nfs server/quotad
+
+For bricks:     `gluster volume statedump <volname>`
+
+For nfs server: `gluster volume statedump <volname> nfs`
+
+For quotad:     `gluster volume statedump <volname> quotad`
+
+For brick-processes files will be created in `statedump-directory` with name of the file as `hyphenated-brick-path.<pid>.dump.timestamp`. For all other processes it will be `glusterdump.<pid>.dump.timestamp`.
+
+##How to read statedump
+We shall see snippets of each type of statedump.
+
+First and last lines of the file have starting and ending time of writing the statedump file. Times will be in UTC timezone.
+
+mallinfo return status is printed in the following format. Please read man mallinfo for more information about what each field means.
+###Mallinfo
+```
+[mallinfo]
+mallinfo_arena=100020224 /* Non-mmapped space allocated (bytes) */
+mallinfo_ordblks=69467 /* Number of free chunks */
+mallinfo_smblks=449 /* Number of free fastbin blocks */
+mallinfo_hblks=13 /* Number of mmapped regions */
+mallinfo_hblkhd=20144128 /* Space allocated in mmapped regions (bytes) */
+mallinfo_usmblks=0 /* Maximum total allocated space (bytes) */
+mallinfo_fsmblks=39264 /* Space in freed fastbin blocks (bytes) */
+mallinfo_uordblks=96710112 /* Total allocated space (bytes) */
+mallinfo_fordblks=3310112 /* Total free space (bytes) */
+mallinfo_keepcost=133712 /* Top-most, releasable space (bytes) */
+```
+
+###Data structure allocation stats
+For every xlator data structure memory per translator loaded in the call-graph is displayed in the following format:
+
+For xlator with name: glusterfs
+```
+[global.glusterfs - Memory usage] #[global.xlator-name - Memory usage]
+num_types=119 #It shows the number of data types it is using
+```
+
+Now for each data-type it prints the memory usage.
+
+```
+[global.glusterfs - usage-type gf_common_mt_gf_timer_t memusage]
+#[global.xlator-name - usage-type <tag associated with the data-type> memusage]
+size=112 #num_allocs times the sizeof(data-type) i.e. num_allocs * sizeof (data-type)
+num_allocs=2 #Number of allocations of the data-type which are active at the time of taking statedump.
+max_size=168 #max_num_allocs times the sizeof(data-type) i.e. max_num_allocs * sizeof (data-type)
+max_num_allocs=3 #Maximum number of active allocations at any point in the life of the process.
+total_allocs=7 #Number of times this data is allocated in the life of the process.
+```
+
+###Mempools
+
+Mempools are optimization to reduce the number of allocations of a data type. If we create a mem-pool of lets say 1024 elements for a data-type, new elements will be allocated from heap using syscalls like calloc, only if all the 1024 elements in the pool are in active use.
+
+Memory pool allocated by each xlator is displayed in the following format:
+
+```
+[mempool] #Section name
+-----=-----
+pool-name=fuse:fd_t #pool-name=<xlator-name>:<data-type>
+hot-count=1 #number of mempool elements that are in active use. i.e. for this pool it is the number of 'fd_t' s in active use.
+cold-count=1023 #number of mempool elements that are not in use. If a new allocation is required it will be served from here until all the elements in the pool are in use i.e. cold-count becomes 0.
+padded_sizeof=108 #Each mempool element is padded with a doubly-linked-list + ptr of mempool + is-in-use info to operate the pool of elements, this size is the element-size after padding
+pool-misses=0 #Number of times the element had to be allocated from heap because all elements from the pool are in active use.
+alloc-count=314 #Number of times this type of data is allocated through out the life of this process. This may include pool-misses as well.
+max-alloc=3 #Maximum number of elements from the pool in active use at any point in the life of the process. This does *not* include pool-misses.
+max-stdalloc=0 #Maximum number of allocations from heap that are in active use at any point in the life of the process.
+```
+
+###Iobufs
+```
+[iobuf.global]
+iobuf_pool=0x1f0d970 #The memory pool for iobufs
+iobuf_pool.default_page_size=131072 #The default size of iobuf (if no iobuf size is specified the default size is allocated)
+#iobuf_arena: One arena represents a group of iobufs of a particular size
+iobuf_pool.arena_size=12976128 # The initial size of the iobuf pool (doesn't include the stdalloc'd memory or the newly added arenas)
+iobuf_pool.arena_cnt=8 #Total number of arenas in the pool
+iobuf_pool.request_misses=0 #The number of iobufs that were stdalloc'd (as they exceeded the default max page size provided by iobuf_pool).
+```
+
+There are 3 lists of arenas
+
+1. Arena list: arenas allocated during iobuf pool creation and the arenas that are in use(active_cnt != 0) will be part of this list.
+2. Purge list: arenas that can be purged(no active iobufs, active_cnt == 0).
+3. Filled list: arenas without free iobufs.
+
+```
+[purge.1] #purge.<S.No.>
+purge.1.mem_base=0x7fc47b35f000 #The address of the arena structure
+purge.1.active_cnt=0 #The number of iobufs active in that arena
+purge.1.passive_cnt=1024 #The number of unused iobufs in the arena
+purge.1.alloc_cnt=22853 #Total allocs in this pool(number of times the iobuf was allocated from this arena)
+purge.1.max_active=7 #Max active iobufs from this arena, at any point in the life of this process.
+purge.1.page_size=128 #Size of all the iobufs in this arena.
+
+[arena.5] #arena.<S.No.>
+arena.5.mem_base=0x7fc47af1f000
+arena.5.active_cnt=0
+arena.5.passive_cnt=64
+arena.5.alloc_cnt=0
+arena.5.max_active=0
+arena.5.page_size=32768
+```
+
+If the active_cnt of any arena is non zero, then the statedump will also have the iobuf list.
+```
+[arena.6.active_iobuf.1] #arena.<S.No>.active_iobuf.<iobuf.S.No.>
+arena.6.active_iobuf.1.ref=1 #refcount of the iobuf
+arena.6.active_iobuf.1.ptr=0x7fdb921a9000 #address of the iobuf
+
+[arena.6.active_iobuf.2]
+arena.6.active_iobuf.2.ref=1
+arena.6.active_iobuf.2.ptr=0x7fdb92189000
+```
+
+At any given point in time if there are lots of filled arenas then that could be a sign of iobuf leaks.
+
+###Call stack
+All the fops received by gluster are handled using call-stacks. Call stack contains the information about uid/gid/pid etc of the process that is executing the fop. Each call-stack contains different call-frames per xlator which handles that fop.
+
+```
+[global.callpool.stack.3] #global.callpool.stack.<Serial-Number>
+stack=0x7fc47a44bbe0 #Stack address
+uid=0 #Uid of the process which is executing the fop
+gid=0 #Gid of the process which is executing the fop
+pid=6223 #Pid of the process which is executing the fop
+unique=2778 #Xlators like afr do copy_frame and perform the operation in a different stack, this id is useful to find out the stacks that are inter-related because of copy-frame
+lk-owner=0000000000000000 #Some of the fuse fops have lk-owner.
+op=LOOKUP #Fop
+type=1 #Type of the op i.e. FOP/MGMT-OP
+cnt=9 #Number of frames in this stack.
+```
+###Call-frame
+Each frame will have information about which xlator the frame belongs to, what is the function it wound to/from and will be unwind to. It also mentions if the unwind happened or not. If we observe hangs in the system and want to find out which xlator is causing it. Take a statedump and see what is the final xlator which is yet to be unwound.
+
+```
+[global.callpool.stack.3.frame.2]#global.callpool.stack.<stack-serial-number>.frame.<frame-serial-number>
+frame=0x7fc47a611dbc #Frame address
+ref_count=0 #Incremented at the time of wind and decremented at the time of unwind.
+translator=r2-client-1 #Xlator this frame belongs to
+complete=0 #if this value is 1 that means this frame is already unwound. 0 if it is yet to unwind.
+parent=r2-replicate-0 #Parent xlator of this frame
+wind_from=afr_lookup #Parent xlator function from which the wind happened
+wind_to=priv->children[i]->fops->lookup
+unwind_to=afr_lookup_cbk #Parent xlator function to which unwind happened
+```
+
+###History of operations in Fuse
+
+Fuse maintains history of operations that happened in fuse.
+
+```
+[xlator.mount.fuse.history]
+TIME=2014-07-09 16:44:57.523364
+message=[0] fuse_release: RELEASE(): 4590:, fd: 0x1fef0d8, gfid: 3afb4968-5100-478d-91e9-76264e634c9f
+
+TIME=2014-07-09 16:44:57.523373
+message=[0] send_fuse_err: Sending Success for operation 18 on inode 3afb4968-5100-478d-91e9-76264e634c9f
+
+TIME=2014-07-09 16:44:57.523394
+message=[0] fuse_getattr_resume: 4591, STAT, path: (/iozone.tmp), gfid: (3afb4968-5100-478d-91e9-76264e634c9f)
+```
+
+###Xlator configuration
+```
+[cluster/replicate.r2-replicate-0] #Xlator type, name information
+child_count=2 #Number of children to the xlator
+#Xlator specific configuration below
+child_up[0]=1
+pending_key[0]=trusted.afr.r2-client-0
+child_up[1]=1
+pending_key[1]=trusted.afr.r2-client-1
+data_self_heal=on
+metadata_self_heal=1
+entry_self_heal=1
+data_change_log=1
+metadata_change_log=1
+entry-change_log=1
+read_child=1
+favorite_child=-1
+wait_count=1
+```
+
+###Graph/inode table
+```
+[active graph - 1]
+
+conn.1.bound_xl./data/brick01a/homegfs.hashsize=14057
+conn.1.bound_xl./data/brick01a/homegfs.name=/data/brick01a/homegfs/inode
+conn.1.bound_xl./data/brick01a/homegfs.lru_limit=16384 #Least recently used size limit
+conn.1.bound_xl./data/brick01a/homegfs.active_size=690 #Number of inodes undergoing some kind of fop to be precise on which there is at least one ref.
+conn.1.bound_xl./data/brick01a/homegfs.lru_size=183 #Number of inodes present in lru list
+conn.1.bound_xl./data/brick01a/homegfs.purge_size=0 #Number of inodes present in purge list
+```
+
+###Inode
+```
+[conn.1.bound_xl./data/brick01a/homegfs.active.324] #324th inode in active inode list
+gfid=e6d337cf-97eb-44b3-9492-379ba3f6ad42 #Gfid of the inode
+nlookup=13 #Number of times lookups happened from the client or from fuse kernel
+fd-count=4 #Number of fds opened on the inode
+ref=11 #Number of refs taken on the inode
+ia_type=1 #Type of the inode. This should be changed to some string :-(
+
+[conn.1.bound_xl./data/brick01a/homegfs.lru.1] #1st inode in lru list. Note that ref count is zero for these inodes.
+gfid=5114574e-69bc-412b-9e52-f13ff087c6fc
+nlookup=5
+fd-count=0
+ref=0
+ia_type=2
+```
+###Inode context
+For each inode per xlator some context could be stored. This context can also be printed in the statedump. Here is the inode ctx of locks xlator
+```
+[xlator.features.locks.homegfs-locks.inode]
+path=/homegfs/users/dfrobins/gfstest/r4/SCRATCH/fort.5102 - path of the file
+mandatory=0
+inodelk-count=5 #Number of inode locks
+lock-dump.domain.domain=homegfs-replicate-0:self-heal #Domain name where self-heals take locks to prevent more than one heal on the same file
+inodelk.inodelk[0](ACTIVE)=type=WRITE, whence=0, start=0, len=0, pid = 18446744073709551615, owner=080b1ada117f0000, client=0xb7fc30, connection-id=compute-30-029.com-3505-2014/06/29-14:46:12:477358-homegfs-client-0-0-1, granted at Sun Jun 29 11:01:00 2014 #Active lock information
+
+inodelk.inodelk[1](BLOCKED)=type=WRITE, whence=0, start=0, len=0, pid = 18446744073709551615, owner=c0cb091a277f0000, client=0xad4f10, connection-id=gfs01a.com-4080-2014/06/29-14:41:36:917768-homegfs-client-0-0-0, blocked at Sun Jun 29 11:04:44 2014 #Blocked lock information
+
+lock-dump.domain.domain=homegfs-replicate-0:metadata #Domain name where metadata operations take locks to maintain replication consistency
+lock-dump.domain.domain=homegfs-replicate-0 #Domain name where entry/data operations take locks to maintain replication consistency
+inodelk.inodelk[0](ACTIVE)=type=WRITE, whence=0, start=11141120, len=131072, pid = 18446744073709551615, owner=080b1ada117f0000, client=0xb7fc30, connection-id=compute-30-029.com-3505-2014/06/29-14:46:12:477358-homegfs-client-0-0-1, granted at Sun Jun 29 11:10:36 2014 #Active lock information
+```
+
+##FAQ
+###How to debug Memory leaks using statedump?
+`https://bugzilla.redhat.com/show_bug.cgi?id=1120151` is one of the bugs which was debugged using statedump to see which data-structure is leaking. Here is the process used to find what the leak is using statedump. According to the bug the observation is that the process memory usage is increasing whenever one of the bricks is wiped in a replicate volume and a `full` self-heal is invoked to heal the contents. Statedump of the process is taken using kill -USR1 `<pid-of-gluster-self-heal-daemon>`.
+```
+grep -w num_allocs glusterdump.5225.dump.1405493251
+num_allocs=77078
+num_allocs=87070
+num_allocs=117376
+....
+
+grep hot-count glusterdump.5225.dump.1405493251
+hot-count=16384
+hot-count=16384
+hot-count=4095
+....
+
+Find the occurrences in the statedump file to figure out the tags.
+```
+grep of the statedump revealed too many allocations for the following data-types under replicate,
+
+1. gf_common_mt_asprintf
+2. gf_common_mt_char
+3. gf_common_mt_mem_pool.
+
+After checking afr-code for allocations with tag `gf_common_mt_char` found `data-self-heal` code path does not free one such allocated memory. `gf_common_mt_mem_pool` suggests that there is a leak in pool memory. `replicate-0:dict_t`, `glusterfs:data_t` and `glusterfs:data_pair_t` pools are using lot of memory, i.e. cold_count is `0` and too many allocations. Checking source code of dict.c revealed that `key` in `dict` is allocated with `gf_common_mt_char` i.e. `2.` tag and value is created using gf_asprintf which in-turn uses `gf_common_mt_asprintf` i.e. `1.`. Browsing the code for leak in self-heal code paths lead to a line which over-writes a variable with new dictionary even when it was already holding a reference to another dictionary. After fixing these leaks, ran the same test to verify that none of the `num_allocs` are increasing even after healing 10,000 files directory hierarchy in statedump of self-heal daemon.
+Please check http://review.gluster.org/8316 for more info about patch/code.
+
+###How to debug hangs because of frame-loss?
+`https://bugzilla.redhat.com/show_bug.cgi?id=994959` is one of the bugs where statedump was helpful in finding where the frame was lost. Here is the process used to find where the hang is using statedump.
+When the hang was observed, statedumps are taken for all the processes. On mount's statedump the following stack is shown:
+```
+[global.callpool.stack.1.frame.1]
+ref_count=1
+translator=fuse
+complete=0
+
+[global.callpool.stack.1.frame.2]
+ref_count=0
+translator=r2-client-1
+complete=1 <<----- Client xlator completed the readdirp call and unwound to afr
+parent=r2-replicate-0
+wind_from=afr_do_readdir
+wind_to=children[call_child]->fops->readdirp
+unwind_from=client3_3_readdirp_cbk
+unwind_to=afr_readdirp_cbk
+
+[global.callpool.stack.1.frame.3]
+ref_count=0
+translator=r2-replicate-0
+complete=0 <<---- Afr xlator is not unwinding for some reason.
+parent=r2-dht
+wind_from=dht_do_readdir
+wind_to=xvol->fops->readdirp
+unwind_to=dht_readdirp_cbk
+
+[global.callpool.stack.1.frame.4]
+ref_count=1
+translator=r2-dht
+complete=0
+parent=r2-io-cache
+wind_from=ioc_readdirp
+wind_to=FIRST_CHILD(this)->fops->readdirp
+unwind_to=ioc_readdirp_cbk
+
+[global.callpool.stack.1.frame.5]
+ref_count=1
+translator=r2-io-cache
+complete=0
+parent=r2-quick-read
+wind_from=qr_readdirp
+wind_to=FIRST_CHILD (this)->fops->readdirp
+unwind_to=qr_readdirp_cbk
+
+```
+`unwind_to` shows that call was unwound to `afr_readdirp_cbk` from client xlator.
+Inspecting that function revealed that afr is not unwinding the stack when fop failed.
+Check http://review.gluster.org/5531 for more info about patch/code changes.