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.
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:
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.
- 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.
- this counts how many bytes were consumed by immutable share uploads. It is incremented at the same time as the ‘close’ counter.
- 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.
- 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).
- 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.
- 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.
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.
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.
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 .
- incremented each time a client asks to upload a file upload_already_present: incremented when the file is already in the grid
- incremented when the file is not already in the grid
- incremented when the helper already has partial ciphertext for the requested upload, indicating that the client is resuming an earlier upload
- this counts how many bytes of ciphertext have been fetched from uploading clients
- 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.
These also track Helper activity:
- how many files are currently being uploaded. 0 when idle.
- how many cache files are present in the incoming/ directory, which holds ciphertext files that are still being fetched from the client
- total size of cache files in the incoming/ directory
- total size of ‘old’ cache files (more than 48 hours)
- how many cache files are present in the encoding/ directory, which holds ciphertext files that are being encoded and uploaded
- total size of cache files in the encoding/ directory
- total size of ‘old’ cache files (more than 48 hours)
- how many seconds since the node process was started
- 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%
- 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.
Using Munin To Graph Stats Values¶
The misc/operations_helpers/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 JSON 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.