Each step is described more fully in the sections below.
We strongly advise making every attempt to complete each step before proceeding to the next.
Rationale.
We have made each of these assumptions numerous times. Each time, we came to regret the assumption. The "obvious" place to measure often turns out to be incomplete, incorrect, or otherwise inappropriate.
We acknowledge that it can be difficult or impossible to complete each step before proceeding to the next. We strongly advise making the attempt.
Clarify the purpose for adding this meter to Geode.
Rationale. Clarifying the purpose of the meter will help you:
Describe as precisely as possible the quantity to measure.
Key elements of the measurement to define:
See below for guidance about each element.
Audience focus. Define the measurement entirely in terms that the audience understands. Define the measurement in such a way that the audience can easily understand which measurements relate most directly to their current goals, questions, and challenges.
Rationale. Defining these elements will help you:
Each meter measures some attribute of some entity. Identify and describe the attribute and the type of entity.
The attribute. The attribute is the characteristic that we want to measure about some entity.
Example: A geode.cache.entries
gauge measures the number of entries in some local region.
Example: A jvm.memory.used
gauge measures the amount memory in use from some pool of memory.
The type of entity. The entity is the thing whose attribute we want to measure.
Example: Each geode.cache.entries
gauge reports the number of entries in a particular local region: That part of a region served by a particular cache server. The measurement is about that local region. The type of entity in this case is local region. We use a region tag to identify the particular local region measured by each meter.
Example: Each jvm.memory.used
gauge measures the amount memory in use in a particular pool of memory. The measurement is about that pool of memory. The type of entity is in this case pool of memory. We use an id tag to identify the particular pool of memory measured by each meter.
The smallest entity. In general, we want to identify the smallest entity that we are interested in that has the attribute. This gives users insight into Because we will add tags that identify interesting scopes that encompass the entity, the user's monitoring system can aggregate the meters from the individually measured entities to compute metrics the measured attribute in larger scopes.
Example: Each geode.cache.entries
gauge reports the number of entries in a particular local region. Later we will add tags to each meter that identify larger scopes, and the user can use those tags aggregate these local region entry counts. The user can, for example:
geode.cache.entries
for all regions in a given server.geode.cache.entries
for a given region across all servers.geode.cache.entries
for all regions across all servers in a given cluster.What affects the attribute. Identify the operations, events, or conditions that cause the attribute to change. Focus on causes that are meaningful to your audience. The user will use your meter to make inferences about those operations, events, and conditions. Identifying these causes will be useful as you identify potential instrumentation sites.
Each measurement measures within one or more scopes of interest to your audience. To identify those scopes, look for various boundaries that encompass the entity being measured, or in which the entity participates.
Example: Each geode.cache.entries
gauge measures within several scopes:
As the example shows, there are several kinds of boundaries to consider:
The example also shows that:
Audience focus. Identify scopes of interest to your audience—those scopes that your audience may wish to use to select and sort measurements for display and analysis. Of particular interest are the scopes that help to identify attribute being measured.
Rationale. Defining the scope of the measurement will help you:
You may wish to report measurements selectively, either by reporting a measurement only in certain circumstances, or by reporting a given measurement differently in different circumstances.
Key questions:
Deciding whether to measure. You may wish to measure the attribute (or whether to report a measurement) only under certain conditions.
Example: As we initially defined the geode.function.executions
timer, we intended to report only executions of user-defined functions, and not functions defined internally by Geode. Though we have not implemented this distinction, it is an example of the kind of distinction we considered.
Choosing among meters. You may wish to create multiple meters for the same attribute, and select among them to record measurements in different circumstances.
Example: Geode defines two geode.cache.gets
timers for each region. One timer reports cache hits, and one reports cache misses. Together these two meters report all get operations on the region.
Example: Geode defines two geode.function.executions
timers for each function. One timer reports successful executions, and one reports failed executions. Together these two meters report all executions of the function.
Rationale. Defining the selection criteria for the measurement will help you:
Select the general type of meter you want to use to report measurements:
Select the category of meter that best suits the nature of the measurement.
The Micrometer library defines Java interfaces and classes that represent several variations of these categories. For details, see Instrument the Code, below.
Identify the attribute. Name each meter in a way that clearly identifies the attribute it measures.
Example: jvm.memory.used
identifies that the gauge reports some amount of JVM memory used.
Example: geode.function.executions
identifies that the timer reports the number and durations of function executions.
Example: geode.cache.entries
identifies that the gauge reports a number of entries.
Consider (with caution) identifying the entity type. Consider including the entity type in the name, though it is often (or usually) better to omit it.
Example: geode.function.executions
identifies that the meter reports executions of a function. Executions is the attribute being reported. Function is the type of entity whose executions are being reported.
Before including the entity type in the meter name, consider:
Example: We considered (and rejected) geode.cache.region.entries
, which would identify that the meter reports not on the cache as a whole, but on a particular region. In the end, we decided that the region
tag sufficed to identify the kind of entity whose entry count the meter reports.
Style. After reviewing the naming conventions of meters packaged with Micrometer, we have adopted these style guidelines for naming meters:
geode
to indicate that the meter reports a geode-specific attribute.Concisely describe the meter, including all key details of your definition.
Example (geode.cache.gets
): "Total time and count for GET requests from Java or native clients."
Note how this description identifies an important boundary of measurement: It measures only those GET requests from Java clients and native clients. Including such details in your description helps your audience understand what is included in the measurement and what is excluded.
If the unit of measure is not obvious from the meter name, identify the unit of measure.
A tag is a key/value pair that represents some detail about the source or circumstances of a measurement.
General advice:
Example: The geode.cache.gets
meter has these tags:
region
tag identifies the entity whose get operations are reported by the meter.result
tag describes a circumstance under which this meter is selected to report a measurement: Cache hit or cache miss.The geode.cache.gets
meter also has these pre-defined tags, which Geode automatically adds to every meter:
member
tag identifies a scope: The member that served the get operations.host
tag identifies a scope: The host on which the member is running.cluster
identifies a scope: The cluster in which the region exists.member_type
tag describes a scope by giving additional facts: The type of the member.Example: The jvm.memory.used
meter (defined by Micrometer) has these tags:
id
tag identifies the entity whose memory being measured: The specific pool of memory (e.g. PS Eden Space
).area
tag identifies a scope: The memory area that manages the pool (heap
or nonheap
).Pre-defined tags. Geode's metrics framework automatically adds several tags to each meter:
member
: The name of the member in which the meter is registered.member_type
: The type of member in which the meter is registered.host
: The name of the host on which the member is running.cluster
: The ID of the cluster that includes the member.You do not need to add these tags yourself.
Tag names and values. Micrometer does not allow null tag keys and tag values. Some meter registry implementations do not allow empty tag values.
Meter ID = name + tags. A meter is identified not only by its name, but by its name and its tags. Thus each combination of name and tags creates a distinct meter.
Combinations of tag keys. Within a single meter registry, make sure that every meter with a given name has exactly the same set of tag keys:
foo
tag, then every meter with the same name must also have a foo
tag.foo
tag, then no meter with the same name may have a foo
tag.This restriction arises from certain meter registry implementations, such as Micrometer's PrometheusMeterRegistry
, that users may wish to use to publish Geode's meters to external monitoring systems.
Note that it is specifically the PrometheusMeterRegistry
, and not Prometheus itself, that enforces the restriction. Prometheus appears to allow similarly-named meters to have different sets of tag keys. This means it is permissible (by Prometheus, at least) for tag keys to differ between Geode instances.
We have not tested other monitoring systems to verify whether they similarly allow tag keys to differ between Geode instances.
Note also that this restriction applies only to the set of tag keys. Tag values may vary freely from meter to meter.
General advice (details TBD):
General advice (details in sections below):
Micrometer defines a number of meter types. See the Micrometer documentation for details. Geode adds several custom meter types (noted below) that associate meters with stats.
Choose the appropriate meter implementation depending on:
Counters. A counter represents a monotonic increasing quantity. Each counter has a count()
method that reports its measured value.
Counter
accumulates the values reported to its increment()
methods and stores the accumulated value. Use a Counter
when no existing source naturally accumulates or computes the desired count, and you do not wish to report the count via a stat.FunctionCounter
retrieves a fresh measurement from a supplier or other object each time its count()
method is called. Use a FunctionCounter
when an existing non-stat source naturally accumulates or computes the desired count.LegacyStatCounter
(a custom Geode meter type) accumulates the values reported to its increment()
methods, and forwards each increment to both an associated stat and a registered Counter
. Use a LegacyStatCounter
when you want to report identical counts through both a stat and a meter.Gauges. A gauge represents a quantity that can go up or down. Each gauge has a value()
method that reports its measured value.
Gauge
retrieves a fresh measurement from a supplier or other object each time value()
is called. Use a Gauge
when an existing non-stat source naturally accumulates or computes the desired value.TimeGauge
represents an instant or duration, and retrieves a fresh measurement from a supplier or other object each time value()
method is called. Use a TimeGauge
when an existing non-stat source naturally accumulates or computes the desired value.Timers. A timer represents both the total number of occurrences of some event and the total durations of those events. Each timer has a count()
method that reports the number events and a totalTime()
method that reports the total duration of events.
record()
methods and stores the accumulated count and duration. Use a Timer if no existing source naturally accumulates or computes the desired counts and durations, and you do not wish to report the measurements via stats.FunctionTimer
retrieves the relevant fresh measurement from an object each time count()
or totalTime()
is called. Use a FunctionTimer when an existing non-stat source naturally accumulates or stores the desired counts and durations.LegacyStatTimer
(a custom Geode meter type) accumulates the counts and durations reported to its record()
methods, and forwards the increments both to associated stats and to a registered Timer. Use a LegacyStatTimer
when you want to report identical counts and durations through both stats and meters.Encapsulate meters in stats classes. Create and register meters only in stats classes. Interact with meters only in stats classes. Use stats classes to manage the lifetime of meters.
Rationale. Much existing Geode code already uses one or more domain-specific stats classes for instrumentation. Placing meters in existing stats classes avoids complicating the domain code with additional instrumentation noise.
Even if no relevant stats class exists, creating a new stats class to encapsulate meters allows the instrumented code to focus on reporting domain events (e.g. reporting a get operation just finished) rather than on the non-domain details of what and how to measure. And adding a stats class allows instrumenting the code using an already ubiquitous style of instrumentation.
Adding or changing a stats class. It is uncommon for an existing stats method to know exactly the information required for a new meter.
endGet()
) and not the details of what it measures (e.g. incGetCount()
).During cache creation, Geode automatically creates and configures its meter registry. The registry is managed by a "metrics service" owned by the InternalDistributedSystem
. You can obtain the meter registry through the InternalDistributedSystem
or, for convenience, from the InternalCache
:
MeterRegistry meterRegistry = internalDistributedSystem.getMeterRegistry();
MeterRegistry meterRegistry = internalCache.getMeterRegistry();
The code you are instrumenting, or the stats class in which you are adding the meters, may also offer access to Geode's meter registry.
Each meter type includes a builder that you can use to progressively define a meter, then register the defined meter with the meter registry.
Timer example:
Timer cacheGetsHitTimer = Timer.builder("geode.cache.gets") .description("Total time and count for GET requests from Java or native clients.") .tag("region", region.getName()) .tag("result", "hit") .register(meterRegistry) |
Gauge example:
Gauge entriesGauge = Gauge.builder("geode.cache.entries", region::getLocalSize) .description("Current number of entries in the region.") .tag("region", region.getName()) .tag("data.policy", region.getDataPolicy().toString()) .baseUnit("entries") .register(meterRegistry); |
Note that when you build a Gauge
, you must tell it how to make a measurement. In this example, line 1 configures the gauge to use a Supplier<Number>
(defined by the region::getLocalSize
method reference) to measure the entry count.
An alternate builder()
method takes a T
object and a ToDoubleFunction<T>
, and creates its own measurement supplier that applies the given function to the given object.
FunctionCounter
and FunctionTimer
are configured similarly. You must tell them how to make their measurements.
LegacyStatCounter example:
Counter eventsReceivedCounter = LegacyStatCounter.builder("geode.gateway.receiver.events") .longStatistic(stats, eventsReceivedId) .description("total number events across the batched received by this GatewayReceiver") .baseUnit("operations") .register(meterRegistry); |
Note that line 2 links the LegacyStatCounter
to a specific statistic (eventsReceivedId
) in a specific Statistics
instance (stats
).
The LegacyStatCounter
builder also has a doubleStatistic
method that links the counter to a double
stat.
LegacyStatTimer
is configured similarly, using builder methods that allow you to forward its count and duration increments to associated long
or double
stats.
Give each meter the same lifetime as the entity whose attributes it measures:
close()
method to remove all of its meters from the registry and close them.stats.close()
when the relevant entity is destroyed, removed, or closed.Example: Each geode.cache.entries
meter reports the number of entries in a given region. Each region's geode.cache.entries
meter should be registered when the region is created and removed from the registry and closed when the region is destroyed.
Rationale: Each meter consumes memory. Publishing each meter consumes CPU cycles. In long-running systems, where the measured objects come and go, leftover meters can accumulate, consuming an increasing amount of memory and CPU time.
Geode's of Micrometer allows the user to publish the measurements to external monitoring systems for long-term storage. As a result, it is unnecessary for Geode to retain meters that measure objects that no longer exist.
Do not create meters whose values can be derived from other meters. For example:
Rationale. External monitoring systems can compute these derived values from the series of measurements over time.