tahoe-lafs/docs/stats.rst

Tahoe Statistics

1. Overview
2. Statistics Categories
3. Running a Tahoe Stats-Gatherer Service
4. Using Munin To Graph Stats Values

Overview

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 upload.

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). Percentiles are only reported in the case of a sufficient number of observations for unambiguous interpretation. For example, the 99.9th percentile is (at the level of thousandths precision) 9 thousandths greater than the 99th percentile for sample sizes greater than or equal to 1000, thus the 99.9th percentile is only reported for samples of 1000 or more observations.

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. It merely gatherers statistics from many nodes into a single place: it does not do any actual analysis.

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.

The first time it is started, the gatherer will listen on a random unused TCP port, so it should not conflict with anything else that you have running on that host at that time. On subsequent runs, it will re-use the same port (to keep its FURL consistent). To explicitly control which port it uses, write the desired portnumber into a file named "portnum" (i.e. $BASEDIR/portnum), and the next time the gatherer is started, it will start listening on the given port. The portnum file is actually a "strports specification string", as described in configuration.

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/operations_helpers/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 e.g. 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 plugins 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.