[
https://issues.apache.org/jira/browse/FLINK-5529?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=15839971#comment-15839971
]
ASF GitHub Bot commented on FLINK-5529:
---------------------------------------
Github user fhueske commented on a diff in the pull request:
https://github.com/apache/flink/pull/3191#discussion_r98028880
--- Diff: docs/dev/windows.md ---
@@ -795,15 +821,17 @@ necessarily the ones that arrive first or last.
## Allowed Lateness
-When working with *event-time* windowing it can happen that elements
arrive late, *i.e.* the watermark that Flink uses to
+When working with *event-time* windowing, it can happen that elements
arrive late, *i.e.* the watermark that Flink uses to
keep track of the progress of event-time is already past the end timestamp
of a window to which an element belongs. See
[event time](./event_time.html) and especially [late
elements](./event_time.html#late-elements) for a more thorough
discussion of how Flink deals with event time.
-By default, late elements are dropped if their associated window was
already evaluated. However,
+By default, late elements are dropped when the watermark is past the end
of the window. However,
Flink allows to specify a maximum *allowed lateness* for window operators.
Allowed lateness
-specifies by how much time elements can be late before they are dropped.
Elements that arrive
-within the allowed lateness of a window are still added to the window and
trigger an immediate evaluation of the window which might emit elements.
+specifies by how much time elements can be late before they are dropped,
and its default value is 0.
+Elements that arrive after the watermark is past the end of the window but
before it passes the end of
+window plus the allowed lateness, are still added to the window. Depending
on the trigger used,
--- End diff --
"passes the end of window" -> "**passed** the end of **the** window"
> Improve / extends windowing documentation
> -----------------------------------------
>
> Key: FLINK-5529
> URL: https://issues.apache.org/jira/browse/FLINK-5529
> Project: Flink
> Issue Type: Sub-task
> Components: Documentation
> Reporter: Stephan Ewen
> Assignee: Kostas Kloudas
> Fix For: 1.2.0, 1.3.0
>
>
> Suggested Outline:
> {code}
> Windows
> (0) Outline: The anatomy of a window operation
> stream
> [.keyBy(...)] <- keyed versus non-keyed windows
> .window(...) <- required: "assigner"
> [.trigger(...)] <- optional: "trigger" (else default trigger)
> [.evictor(...)] <- optional: "evictor" (else no evictor)
> [.allowedLateness()] <- optional, else zero
> .reduce/fold/apply() <- required: "function"
> (1) Types of windows
> - tumble
> - slide
> - session
> - global
> (2) Pre-defined windows
> timeWindow() (tumble, slide)
> countWindow() (tumble, slide)
> - mention that count windows are inherently
> resource leaky unless limited key space
> (3) Window Functions
> - apply: most basic, iterates over elements in window
>
> - aggregating: reduce and fold, can be used with "apply()" which will get
> one element
>
> - forward reference to state size section
> (4) Advanced Windows
> - assigner
> - simple
> - merging
> - trigger
> - registering timers (processing time, event time)
> - state in triggers
> - life cycle of a window
> - create
> - state
> - cleanup
> - when is window contents purged
> - when is state dropped
> - when is metadata (like merging set) dropped
> (5) Late data
> - picture
> - fire vs fire_and_purge: late accumulates vs late resurrects (cf
> discarding mode)
>
> (6) Evictors
> - TDB
>
> (7) State size: How large will the state be?
> Basic rule: Each element has one copy per window it is assigned to
> --> num windows * num elements in window
> --> example: tumbline is one copy, sliding(n,m) is n/m copies
> --> per key
> Pre-aggregation:
> - if reduce or fold is set -> one element per window (rather than num
> elements in window)
> - evictor voids pre-aggregation from the perspective of state
> Special rules:
> - fold cannot pre-aggregate on session windows (and other merging windows)
> (8) Non-keyed windows
> - all elements through the same windows
> - currently not parallel
> - possible parallel in the future when having pre-aggregation functions
> - inherently (by definition) produce a result stream with parallelism one
> - state similar to one key of keyed windows
> {code}
--
This message was sent by Atlassian JIRA
(v6.3.4#6332)
