@InterfaceAudience.Public @InterfaceStability.Unstable
See: Description
Interface  Description 

IOStatistics 
IO Statistics.

IOStatisticsAggregator 
Interface exported by classes which support
aggregation of
IOStatistics . 
Class  Description 

DurationStatisticSummary 
Summary of duration tracking statistics
as extracted from an IOStatistics instance.

IOStatisticsLogging 
Utility operations convert IO Statistics sources/instances
to strings, especially for robustly logging.

IOStatisticsSnapshot 
Snapshot of statistics from a different source.

IOStatisticsSupport 
Support for working with IOStatistics.

MeanStatistic 
A mean statistic represented as the sum and the sample count;
the mean is calculated on demand.

StoreStatisticNames 
Common statistic names for object store operations..

StreamStatisticNames 
These are common statistic names.

This package defines two interfaces:
IOStatisticsSource
:
a source of statistic data, which can be retrieved
through a call to
IOStatisticsSource.getIOStatistics()
.
IOStatistics
the statistics retrieved
from a statistics source.
The retrieved statistics may be an immutable snapshot in which case to get
updated statistics another call to
IOStatisticsSource.getIOStatistics()
must be made. Or they may be dynamic in which case every time a specific
statistic is retrieved, the latest version is returned. Callers should assume
that if a statistics instance is dynamic, there is no atomicity when querying
multiple statistics. If the statistics source was a closeable object (e.g. a
stream), the statistics MUST remain valid after the stream is closed.
Use pattern:
An application probes an object (filesystem, stream etc) to see if it
implements IOStatisticsSource
, and, if it is,
calls getIOStatistics()
to get its statistics.
If this is nonnull, the client has statistics on the current
state of the statistics.
The expectation is that a statistics source is dynamic: when a value is looked up the most recent values are returned. When iterating through the set, the values of the iterator SHOULD be frozen at the time the iterator was requested.
These statistics can be used to: log operations, profile applications, and make assertions about the state of the output.
The names of statistics are a matter of choice of the specific source.
However, StoreStatisticNames
contains a
set of names recommended for object store operations.
StreamStatisticNames
declares
recommended names for statistics provided for
input and output streams.
Utility classes:
IOStatisticsSupport
.
General support, including the ability to take a serializable
snapshot of the current state of an IOStatistics instance.
IOStatisticsLogging
.
Methods for robust/ondemand string conversion, designed
for use in logging statements and toString()
implementations.
IOStatisticsSnapshot
.
A static snaphot of statistics which can be marshalled via
java serialization or as JSON via jackson. It supports
aggregation, so can be used to generate aggregate statistics.
Implementors notes:
IOStatisticsSource
.
(i.e. not shared the way StorageStatistics are)
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