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Add docs/stats.py, explaining Tahoe stats, the gatherer, and the munin plugins.

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Brian Warner 2009-12-23 00:24:00 -05:00
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= Tahoe Statistics =
Each Tahoe node collects and publishes statistics about its operations as it
runs. These include counters of how many files have been uploaded and
downloaded, CPU usage information, performance numbers like latency of
storage server operations, and available disk space.
The easiest way to see the stats for any given node is use the web interface.
From the main "Welcome Page", follow the "Operational Statistics" link inside
the small "This Client" box. If the welcome page lives at
http://localhost:3456/, then the statistics page will live at
http://localhost:3456/statistics . This presents a summary of the stats
block, along with a copy of the raw counters. To obtain just the raw counters
(in JSON format), use /statistics?t=json instead.
= Statistics Categories =
The stats dictionary contains two keys: 'counters' and 'stats'. 'counters'
are strictly counters: they are reset to zero when the node is started, and
grow upwards. 'stats' are non-incrementing values, used to measure the
current state of various systems. Some stats are actually booleans, expressed
as '1' for true and '0' for false (internal restrictions require all stats
values to be numbers).
Under both the 'counters' and 'stats' dictionaries, each individual stat has
a key with a dot-separated name, breaking them up into groups like
'cpu_monitor' and 'storage_server'.
The currently available stats (as of release 1.6.0 or so) are described here:
counters.storage_server.*: this group counts inbound storage-server
operations. They are not provided by client-only
nodes which have been configured to not run a
storage server (with [storage]enabled=false in
tahoe.cfg)
allocate, write, close, abort: these are for immutable file uploads.
'allocate' is incremented when a client asks
if it can upload a share to the server.
'write' is incremented for each chunk of
data written. 'close' is incremented when
the share is finished. 'abort' is
incremented if the client abandons the
uploaed.
get, read: these are for immutable file downloads. 'get' is incremented
when a client asks if the server has a specific share. 'read' is
incremented for each chunk of data read.
readv, writev: these are for immutable file creation, publish, and
retrieve. 'readv' is incremented each time a client reads
part of a mutable share. 'writev' is incremented each time a
client sends a modification request.
add-lease, renew, cancel: these are for share lease modifications.
'add-lease' is incremented when an 'add-lease'
operation is performed (which either adds a new
lease or renews an existing lease). 'renew' is
for the 'renew-lease' operation (which can only
be used to renew an existing one). 'cancel' is
used for the 'cancel-lease' operation.
bytes_freed: this counts how many bytes were freed when a 'cancel-lease'
operation removed the last lease from a share and the share
was thus deleted.
bytes_added: this counts how many bytes were consumed by immutable share
uploads. It is incremented at the same time as the 'close'
counter.
stats.storage_server.*:
allocated: this counts how many bytes are currently 'allocated', which
tracks the space that will eventually be consumed by immutable
share upload operations. The stat is increased as soon as the
upload begins (at the same time the 'allocated' counter is
incremented), and goes back to zero when the 'close' or 'abort'
message is received (at which point the 'disk_used' stat should
incremented by the same amount).
disk_total
disk_used
disk_free_for_root
disk_free_for_nonroot
disk_avail
reserved_space: these all reflect disk-space usage policies and status.
'disk_total' is the total size of disk where the storage
server's BASEDIR/storage/shares directory lives, as reported
by /bin/df or equivalent. 'disk_used', 'disk_free_for_root',
and 'disk_free_for_nonroot' show related information.
'reserved_space' reports the reservation configured by the
tahoe.cfg [storage]reserved_space value. 'disk_avail'
reports the remaining disk space available for the Tahoe
server after subtracting reserved_space from disk_avail. All
values are in bytes.
accepting_immutable_shares: this is '1' if the storage server is currently
accepting uploads of immutable shares. It may be
'0' if a server is disabled by configuration, or
if the disk is full (i.e. disk_avail is less
than reserved_space).
total_bucket_count: this counts the number of 'buckets' (i.e. unique
storage-index values) currently managed by the storage
server. It indicates roughly how many files are managed
by the server.
latencies.*.*: these stats keep track of local disk latencies for
storage-server operations. A number of percentile values are
tracked for many operations. For example,
'storage_server.latencies.readv.50_0_percentile' records the
median response time for a 'readv' request. All values are in
seconds. These are recorded by the storage server, starting
from the time the request arrives (post-deserialization) and
ending when the response begins serialization. As such, they
are mostly useful for measuring disk speeds. The operations
tracked are the same as the counters.storage_server.* counter
values (allocate, write, close, get, read, add-lease, renew,
cancel, readv, writev). The percentile values tracked are:
mean, 01_0_percentile, 10_0_percentile, 50_0_percentile,
90_0_percentile, 95_0_percentile, 99_0_percentile,
99_9_percentile. (the last value, 99.9 percentile, means that
999 out of the last 1000 operations were faster than the
given number, and is the same threshold used by Amazon's
internal SLA, according to the Dynamo paper).
counters.uploader.files_uploaded
counters.uploader.bytes_uploaded
counters.downloader.files_downloaded
counters.downloader.bytes_downloaded
These count client activity: a Tahoe client will increment these when it
uploads or downloads an immutable file. 'files_uploaded' is incremented by
one for each operation, while 'bytes_uploaded' is incremented by the size of
the file.
counters.mutable.files_published
counters.mutable.bytes_published
counters.mutable.files_retrieved
counters.mutable.bytes_retrieved
These count client activity for mutable files. 'published' is the act of
changing an existing mutable file (or creating a brand-new mutable file).
'retrieved' is the act of reading its current contents.
counters.chk_upload_helper.*
These count activity of the "Helper", which receives ciphertext from clients
and performs erasure-coding and share upload for files that are not already
in the grid. The code which implements these counters is in
src/allmydata/immutable/offloaded.py .
upload_requests: incremented each time a client asks to upload a file
upload_already_present: incremented when the file is already in the grid
upload_need_upload: incremented when the file is not already in the grid
resumes: incremented when the helper already has partial ciphertext for
the requested upload, indicating that the client is resuming an
earlier upload
fetched_bytes: this counts how many bytes of ciphertext have been fetched
from uploading clients
encoded_bytes: this counts how many bytes of ciphertext have been
encoded and turned into successfully-uploaded shares. If no
uploads have failed or been abandoned, encoded_bytes should
eventually equal fetched_bytes.
stats.chk_upload_helper.*
These also track Helper activity:
active_uploads: how many files are currently being uploaded. 0 when idle.
incoming_count: how many cache files are present in the incoming/ directory,
which holds ciphertext files that are still being fetched
from the client
incoming_size: total size of cache files in the incoming/ directory
incoming_size_old: total size of 'old' cache files (more than 48 hours)
encoding_count: how many cache files are present in the encoding/ directory,
which holds ciphertext files that are being encoded and
uploaded
encoding_size: total size of cache files in the encoding/ directory
encoding_size_old: total size of 'old' cache files (more than 48 hours)
stats.node.uptime: how many seconds since the node process was started
stats.cpu_monitor.*:
.1min_avg, 5min_avg, 15min_avg: estimate of what percentage of system CPU
time was consumed by the node process, over
the given time interval. Expressed as a
float, 0.0 for 0%, 1.0 for 100%
.total: estimate of total number of CPU seconds consumed by node since
the process was started. Ticket #472 indicates that .total may
sometimes be negative due to wraparound of the kernel's counter.
stats.load_monitor.*:
When enabled, the "load monitor" continually schedules a one-second
callback, and measures how late the response is. This estimates system load
(if the system is idle, the response should be on time). This is only
enabled if a stats-gatherer is configured.
.avg_load: average "load" value (seconds late) over the last minute
.max_load: maximum "load" value over the last minute
= Running a Tahoe Stats-Gatherer Service =
The "stats-gatherer" is a simple daemon that periodically collects stats from
several tahoe nodes. It could be useful, e.g., in a production environment,
where you want to monitor dozens of storage servers from a central management
host.
The stats gatherer listens on a network port using the same Foolscap
connection library that Tahoe clients use to connect to storage servers.
Tahoe nodes can be configured to connect to the stats gatherer and publish
their stats on a periodic basis. (in fact, what happens is that nodes connect
to the gatherer and offer it a second FURL which points back to the node's
"stats port", which the gatherer then uses to pull stats on a periodic basis.
The initial connection is flipped to allow the nodes to live behind NAT
boxes, as long as the stats-gatherer has a reachable IP address)
The stats-gatherer is created in the same fashion as regular tahoe client
nodes and introducer nodes. Choose a base directory for the gatherer to live
in (but do not create the directory). Then run:
tahoe create-stats-gatherer $BASEDIR
and start it with "tahoe start $BASEDIR". Once running, the gatherer will
write a FURL into $BASEDIR/stats_gatherer.furl .
To configure a Tahoe client/server node to contact the stats gatherer, copy
this FURL into the node's tahoe.cfg file, in a section named "[client]",
under a key named "stats_gatherer.furl", like so:
[client]
stats_gatherer.furl = pb://qbo4ktl667zmtiuou6lwbjryli2brv6t@192.168.0.8:49997/wxycb4kaexzskubjnauxeoptympyf45y
or simply copy the stats_gatherer.furl file into the node's base directory
(next to the tahoe.cfg file): it will be interpreted in the same way.
Once running, the stats gatherer will create a standard python "pickle" file
in $BASEDIR/stats.pickle . Once a minute, the gatherer will pull stats
information from every connected node and write them into the pickle. The
pickle will contain a dictionary, in which node identifiers (known as "tubid"
strings) are the keys, and the values are a dict with 'timestamp',
'nickname', and 'stats' keys. d[tubid][stats] will contain the stats
dictionary as made available at http://localhost:3456/statistics?t=json . The
pickle file will only contain the most recent update from each node.
Other tools can be built to examine these stats and render them into
something useful. For example, a tool could sum the
"storage_server.disk_avail' values from all servers to compute a
total-disk-available number for the entire grid (however, the "disk watcher"
daemon, in misc/spacetime/, is better suited for this specific task).
= Using Munin To Graph Stats Values =
The misc/munin/ directory contains various plugins to graph stats for Tahoe
nodes. They are intended for use with the Munin system-management tool, which
typically polls target systems every 5 minutes and produces a web page with
graphs of various things over multiple time scales (last hour, last month,
last year).
Most of the plugins are designed to pull stats from a single Tahoe node, and
are configured with the http://localhost:3456/statistics?t=json URL. The
"tahoe_stats" plugin is designed to read from the pickle file created by the
stats-gatherer. Some are to be used with the disk watcher, and a few (like
tahoe_nodememory) are designed to watch the node processes directly (and must
therefore run on the same host as the target node).
Please see the docstrings at the beginning of each plugin for details, and
the "tahoe-conf" file for notes about configuration and installing these
plugins into a Munin environment.