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Update documentation

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Andrew Noyes 2020-06-28 20:56:44 +00:00
parent 1c30adce74
commit b1d5e99494
2 changed files with 14 additions and 23 deletions
documentation/sphinx/source
developer-guide.rst
fdbclient
NativeAPI.actor.cpp

35
documentation/sphinx/source/developer-guide.rst

@ -845,30 +845,21 @@ Metrics module
Reads in the metrics module are not transactional and may require rpcs to complete.
The key ``\xff\xff/metrics/data_distribution_stats/<begin>`` represent stats about the shard that begins at ``<begin>``. The value is a json object with a "ShardBytes" field. More fields may be added in the future.
``\xff\xff/metrics/data_distribution_stats/<begin>`` represent stats about the shard that begins at ``<begin>``
A user can see stats about data distribution like so::
TODO update with "Storages" field, add table with schema like in health keys, and document caveats. ShardBytes is an estimate.
>>> for k, v in db.get_range_startswith('\xff\xff/metrics/data_distribution_stats/'):
>>> for k, v in db.get_range_startswith('\xff\xff/metrics/data_distribution_stats/', limit=3):
... print(k, v)
...
('\xff\xff/metrics/data_distribution_stats/', '{"ShardBytes":330000}')
('\xff\xff/metrics/data_distribution_stats/mako00509', '{"ShardBytes":330000}')
('\xff\xff/metrics/data_distribution_stats/mako0099', '{"ShardBytes":330000}')
('\xff\xff/metrics/data_distribution_stats/mako01468', '{"ShardBytes":297000}')
('\xff\xff/metrics/data_distribution_stats/mako023', '{"ShardBytes":264000}')
('\xff\xff/metrics/data_distribution_stats/mako0289', '{"ShardBytes":297000}')
('\xff\xff/metrics/data_distribution_stats/mako037', '{"ShardBytes":330000}')
('\xff\xff/metrics/data_distribution_stats/mako042', '{"ShardBytes":264000}')
('\xff\xff/metrics/data_distribution_stats/mako0457', '{"ShardBytes":297000}')
('\xff\xff/metrics/data_distribution_stats/mako0524', '{"ShardBytes":264000}')
('\xff\xff/metrics/data_distribution_stats/mako058', '{"ShardBytes":297000}')
('\xff\xff/metrics/data_distribution_stats/mako064', '{"ShardBytes":297000}')
('\xff\xff/metrics/data_distribution_stats/mako0718', '{"ShardBytes":264000}')
('\xff\xff/metrics/data_distribution_stats/mako083', '{"ShardBytes":297000}')
('\xff\xff/metrics/data_distribution_stats/mako0909', '{"ShardBytes":741000}')
('\xff\xff/metrics/data_distribution_stats/', '{"ShardBytes":3828000,"Storages":["697f39751849d70067eabd1b079478a5"]}')
('\xff\xff/metrics/data_distribution_stats/mako00079', '{"ShardBytes":2013000,"Storages":["697f39751849d70067eabd1b079478a5"]}')
('\xff\xff/metrics/data_distribution_stats/mako00126', '{"ShardBytes":3201000,"Storages":["697f39751849d70067eabd1b079478a5"]}')
========================= ======== ===============
**Field** **Type** **Description**
------------------------- -------- ---------------
ShardBytes number An estimate of the sum of kv sizes for this shard.
Storages [string] A list of the storage process ids currently responsible for this shard.
========================= ======== ===============
Keys starting with ``\xff\xff/metrics/health/`` represent stats about the health of the cluster, suitable for application-level throttling.
Some of this information is also available in ``\xff\xff/status/json``, but these keys are significantly cheaper (in terms of server resources) to read.
@ -920,7 +911,7 @@ storageQueue number The number of bytes of mutations that need to
Caveats
~~~~~~~
#. ``\xff\xff/metrics/health/`` These keys may return data that's several seconds old, and the data may not be available for a brief period during recovery. This will be indicated by the keys briefly not being present when read. Clients should be prepared for these keys to be absent.
#. ``\xff\xff/metrics/health/`` These keys may return data that's several seconds old, and the data may not be available for a brief period during recovery. This will be indicated by the keys being absent.
Performance considerations
==========================

2
fdbclient/NativeAPI.actor.cpp

@ -596,7 +596,7 @@ public:
static Standalone<RangeResultRef> healthMetricsToKVPairs(const HealthMetrics& metrics, KeyRangeRef kr) {
Standalone<RangeResultRef> result;
if (kr.contains(LiteralStringRef("\xff\xff/metrics/health/aggregate"))) {
if (kr.contains(LiteralStringRef("\xff\xff/metrics/health/aggregate")) && metrics.worstStorageDurabilityLag != 0) {
json_spirit::mObject statsObj;
statsObj["batchLimited"] = metrics.batchLimited;
statsObj["tpsLimit"] = metrics.tpsLimit;