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WIP

This commit is contained in:
Andrew Noyes 2020-06-28 04:11:13 +00:00
parent 4a584a6f6b
commit 1c30adce74
2 changed files with 10 additions and 5 deletions
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12
documentation/sphinx/source/developer-guide.rst
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@ -849,6 +849,8 @@ The key ``\xff\xff/metrics/data_distribution_stats/<begin>`` represent stats abo
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/'):
... print(k, v)
...
@ -868,10 +870,8 @@ A user can see stats about data distribution like so::
('\xff\xff/metrics/data_distribution_stats/mako083', '{"ShardBytes":297000}')
('\xff\xff/metrics/data_distribution_stats/mako0909', '{"ShardBytes":741000}')
Keys starting with ``\xff\xff/metrics/health/`` represent stats about the health of the cluster, suitable for use for application-level throttling.
Some of this information is also available through ``\xff\xff/status/json``,
but the ``\xff\xff/metrics/health/`` keys are much cheaper to read and may
return data a few seconds old.
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.
>>> for k, v in db.get_range_startswith('\xff\xff/metrics/health/'):
... print(k, v)
@ -917,6 +917,10 @@ storageDurabilityLag number The difference between the newest version and
storageQueue number The number of bytes of mutations that need to be stored in memory on this storage process
========================= ======== ===============
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.
Performance considerations
==========================

3
fdbclient/NativeAPI.actor.cpp
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@ -514,10 +514,11 @@ public:
};
ACTOR Future<Standalone<RangeResultRef>> ddMetricsGetRangeActor(ReadYourWritesTransaction* ryw, KeyRangeRef kr) {
auto keys = kr.removePrefix(ddStatsRange.begin);
state KeyRangeRef keys = kr.removePrefix(ddStatsRange.begin);
state Standalone<VectorRef<DDMetricsRef>> resultWithoutPrefix =
wait(waitDataDistributionMetricsList(ryw->getDatabase(), keys, CLIENT_KNOBS->STORAGE_METRICS_SHARD_LIMIT));
state Standalone<RangeResultRef> result;
ryw->getDatabase()->invalidateCache(keys);
for (const auto& ddMetricsRef_ : resultWithoutPrefix) {
state DDMetricsRef ddMetricsRef = ddMetricsRef_;
// each begin key is the previous end key, thus we only encode the begin key in the result