[GitHub] [flink] dawidwys commented on a change in pull request #18765: [FLINK-26134][docs] Added table with Checkpoint/Savepoint guarantees …

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dawidwys commented on a change in pull request #18765:
URL: https://github.com/apache/flink/pull/18765#discussion_r826988366



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File path: docs/content/docs/ops/state/checkpoints_vs_savepoints.md
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+---
+title: "Checkpoints VS Savepoints"
+weight: 10
+type: docs
+aliases:
+  - /ops/state/checkpoints_vs_savepoints.html
+---
+<!--
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+KIND, either express or implied.  See the License for the
+specific language governing permissions and limitations
+under the License.
+-->
+
+# Checkpoints VS Savepoints
+
+## Overview
+
+Conceptually, Flink's [Savepoints]({{< ref "docs/ops/state/savepoints" >}}) are different from [Checkpoints]({{< ref "docs/ops/state/checkpoints" >}}) 
+in a similar way that backups are different from recovery logs in traditional database systems.
+
+The primary purpose of Checkpoints is to provide a recovery mechanism in case of unexpected job failures. 
+A [Checkpoint's lifecycle]({{< ref "docs/dev/datastream/fault-tolerance/checkpointing" >}}) is managed by Flink, 
+i.e. a Checkpoint is created, owned, and released by Flink - without user interaction. 
+As a method of recovery and being periodically triggered, two main design goals for the Checkpoint implementation are 
+i) being as lightweight to create and ii) being as fast to restore from as possible. 
+Optimizations towards those goals can exploit certain properties, e.g. that the job code doesn't change between the execution attempts. 
+Checkpoints are usually dropped after the job was terminated by the user (except if explicitly configured as retained Checkpoints).
+
+{{< hint info >}}
+- Checkpoints are automatically deleted if the application is terminated by the user 
+(except if checkpoints are explicitly configured to be retained).
+- Checkpoints are stored in state backend-specific (native) data format (may be incremental depending on the specific backend).
+{{< /hint >}}
+
+Although [savepoints]({{< ref "docs/ops/state/savepoints" >}}) are created internally with the same mechanisms as
+checkpoints, they are conceptually different and can be a bit more expensive to produce and restore from and focus
+more on portability and flexibility with respect to changes to the job. 
+Their use case is planned, manual backup and resume. For example, this could be an update of your Flink version, changing your job graph,
+changing parallelism, forking a second job like for a red/blue deployment, and so on.
+
+{{< hint info >}}
+- Savepoints are created, owned and deleted solely by the user. 
+That means, Flink does not delete savepoints neither after job termination nor after
+restore.
+- Savepoints are stored in a state backend independent (canonical) format (Note: Since Flink 1.15, savepoints can be also stored in
+the backend-specific [native]({{< ref "docs/ops/state/savepoints" >}}#savepoint-format) format which is faster to create
+and restore but comes with some limitations.
+{{< /hint >}}
+
+### Capabilities and limitations
+The following table gives an overview of capabilities and limitations for the various types of savepoints and
+checkpoints.
+- ✓ - Flink fully support this type of the snapshot
+- x - Flink doesn't support this type of the snapshot
+- ! - in fact, Flink support this type but officially, Flink doesn't support this type of the snapshot(there is certain level of risk to use it)
+
+| Operation                       | Canonical Savepoint | Native Savepoint | Aligned Checkpoint | Unaligned Checkpoint |
+|:--------------------------------|:--------------------|:-----------------|:-------------------|:---------------------|
+| State backend change            | ✓                   | x                | x                  | x                    |
+| State Processor API(writing)    | ✓                   | x                | x                  | x                    |
+| State Processor API(reading)    | ✓                   | !                | !                  | x                    |
+| Self-contained and relocatable  | ✓                   | ✓                | x                  | x                    |
+| Schema evolution                | ✓                   | !                | !                  | !                    |

Review comment:
       Are the values for `Schema evolution` correct?




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