Add retention to Snapshot Lifecycle Management #46407
Merged
Conversation
This file contains bidirectional Unicode text that may be interpreted or compiled differently than what appears below. To review, open the file in an editor that reveals hidden Unicode characters.
Learn more about bidirectional Unicode characters
* Add base framework for snapshot retention This adds a basic `SnapshotRetentionService` and `SnapshotRetentionTask` to start as the basis for SLM's retention implementation. Relates to #38461 * Remove extraneous 'public' * Use a local var instead of reading class var repeatedly
* Add SnapshotRetentionConfiguration for retention configuration This commit adds the `SnapshotRetentionConfiguration` class and its HLRC counterpart to encapsulate the configuration for SLM retention. Currently only a single parameter is supported as an example (we still need to discuss the different options we want to support and their names) to keep the size of the PR down. It also does not yet include version serialization checks since the original SLM branch has not yet been merged. Relates to #43663 * Fix REST tests * Fix more documentation * Use Objects.equals to avoid NPE * Put `randomSnapshotLifecyclePolicy` in only one place * Occasionally return retention with no configuration
* Implement SnapshotRetentionTask's snapshot filtering and deletion This commit implements the snapshot filtering and deletion for `SnapshotRetentionTask`. Currently only the expire-after age is used for determining whether a snapshot is eligible for deletion. Relates to #43663 * Fix deletes running on the wrong thread * Handle missing or null policy in snap metadata differently * Convert Tuple<String, List<SnapshotInfo>> to Map<String, List<SnapshotInfo>> * Use the `OriginSettingClient` to work with security, enhance logging * Prevent NPE in test by mocking Client
This adds the configuration options for `min_count` and `max_count` as well as the logic for determining whether a snapshot meets this criteria to SLM's retention feature. These options are optional and one, two, or all three can be specified in an SLM policy. Relates to #43663
* Time-bound deletion of snapshots in retention delete function With a cluster that has a large number of snapshots, it's possible that snapshot deletion can take a very long time (especially since deletes currently have to happen in a serial fashion). To prevent snapshot deletion from taking forever in a cluster and blocking other operations, this commit adds a setting to allow configuring a maximum time to spend deletion snapshots during retention. This dynamic setting defaults to 1 hour and is best-effort, meaning that it doesn't hard stop a deletion at an hour mark, but ensures that once the time has passed, all subsequent deletions are deferred until the next retention cycle. Relates to #43663 * Wow snapshots suuuure can take a long time. * Use a LongSupplier instead of actually sleeping * Remove TestLogging annotation * Remove rate limiting
* Add SLM metrics gathering and endpoint
This commit adds the infrastructure to gather metrics about the different SLM actions that a cluster
takes. These actions are stored in `SnapshotLifecycleStats` and perpetuated in cluster state. The
stats stored include the number of snapshots taken, failed, deleted, the number of retention runs,
as well as per-policy counts for snapshots taken, failed, and deleted. It also includes the amount
of time spent deleting snapshots from SLM retention.
This commit also adds an endpoint for retrieving all stats (further commits will expose this in the
SLM get-policy API) that looks like:
```
GET /_slm/stats
{
"retention_runs" : 13,
"retention_failed" : 0,
"retention_timed_out" : 0,
"retention_deletion_time" : "1.4s",
"retention_deletion_time_millis" : 1404,
"policy_metrics" : {
"daily-snapshots2" : {
"snapshots_taken" : 7,
"snapshots_failed" : 0,
"snapshots_deleted" : 6,
"snapshot_deletion_failures" : 0
},
"daily-snapshots" : {
"snapshots_taken" : 12,
"snapshots_failed" : 0,
"snapshots_deleted" : 12,
"snapshot_deletion_failures" : 6
}
},
"total_snapshots_taken" : 19,
"total_snapshots_failed" : 0,
"total_snapshots_deleted" : 18,
"total_snapshot_deletion_failures" : 6
}
```
This does not yet include HLRC for this, as this commit is quite large on its own. That will be
added in a subsequent commit.
Relates to #43663
* Version qualify serialization
* Initialize counters outside constructor
* Use computeIfAbsent instead of being too verbose
* Move part of XContent generation into subclass
* Fix REST action for master merge
* Unused import
This commit records the deletion of snapshots by the retention component of SLM into the SLM history index for the purposes of reviewing operations taken by SLM and alerting.
* Retry SLM retention after currently running snapshot completes This commit adds a ClusterStateObserver to wait until the currently running snapshot is complete before proceeding with snapshot deletion. SLM retention waits for the maximum allowed deletion time for the snapshot to complete, however, the waiting time is not factored into the limit on actual deletions. Relates to #43663 * Increase timeout waiting for snapshot completion * Apply patch From https://github.com/original-brownbear/elasticsearch/commit/2374316f0d1912c9e1498bece195546a1dc60bce.patch * Rename test variables
This adds a check to ensure we take no action during SLM retention if ILM is currently stopped or in the process of stopping. Relates to #43663
* Rewrite SnapshotLifecycleIT as as ESIntegTestCase This commit splits `SnapshotLifecycleIT` into two different tests. `SnapshotLifecycleRestIT` which includes the tests that do not require slow repositories, and `SLMSnapshotBlockingIntegTests` which is now an integration test using `MockRepository` to simulate a snapshot being in progress. Relates to #43663 Resolves #46205 * Add error logging when exceptions are thrown
dakrone
added
>feature
:Data Management/ILM+SLM
|
Pinging @elastic/es-core-features |
|
I think this PR is way too large, and could be split into several smaller ones. For example, integrating with the high-level REST client could be a separate change. Large PRs are incredibly hard to review, I think we all start to lose focus after even a few hundred lines. I also notice there ends up being smaller changes mixed in, for example, the TimeValue change is worth lifting to its own small change, and letting the core/infra team review. |
|
It's worth noting that this is merging a feature branch, and all the changes have been reviewed as part of smaller PRs. I believe the smaller changes impacting things owned by other areas teams were reviewed by the appropriate team at the time, but we can double-check. |
|
Okay, thanks for clarifying. That was not clear from the description at all. |
|
I apologize, I should have clarified that more in the PR description. I was writing it to be as close to a commit message as possible for the squash commit and left that out. |
dakrone
added a commit
to dakrone/elasticsearch
that referenced
this pull request
Sep 9, 2019
This commit adds retention to the existing Snapshot Lifecycle Management feature (elastic#38461) as described in elastic#43663. This allows a user to configure SLM to automatically delete older snapshots based on a number of criteria. An example policy would look like: ``` PUT /_slm/policy/snapshot-every-day { "schedule": "0 30 2 * * ?", "name": "<production-snap-{now/d}>", "repository": "my-s3-repository", "config": { "indices": ["foo-*", "important"] }, // Newly configured retention options "retention": { // Snapshots should be deleted after 14 days "expire_after": "14d", // Keep a maximum of thirty snapshots "max_count": 30, // Keep a minimum of the four most recent snapshots "min_count": 4 } } ``` SLM Retention is run on a scheduled configurable with the `slm.retention_schedule` setting, which supports cron expressions. Deletions are run for a configurable time bounded by the `slm.retention_duration` setting, which defaults to 1 hour. Included in this work is a new SLM stats API endpoint available through ``` json GET /_slm/stats ``` That returns statistics about snapshot taken and deleted, as well as successful retention runs, failures, and the time spent deleting snapshots. elastic#45362 has more information as well as an example of the output. These stats are also included when retrieving SLM policies via the API. * Add base framework for snapshot retention (elastic#43605) * Add base framework for snapshot retention This adds a basic `SnapshotRetentionService` and `SnapshotRetentionTask` to start as the basis for SLM's retention implementation. Relates to elastic#38461 * Remove extraneous 'public' * Use a local var instead of reading class var repeatedly * Add SnapshotRetentionConfiguration for retention configuration (elastic#43777) * Add SnapshotRetentionConfiguration for retention configuration This commit adds the `SnapshotRetentionConfiguration` class and its HLRC counterpart to encapsulate the configuration for SLM retention. Currently only a single parameter is supported as an example (we still need to discuss the different options we want to support and their names) to keep the size of the PR down. It also does not yet include version serialization checks since the original SLM branch has not yet been merged. Relates to elastic#43663 * Fix REST tests * Fix more documentation * Use Objects.equals to avoid NPE * Put `randomSnapshotLifecyclePolicy` in only one place * Occasionally return retention with no configuration * Implement SnapshotRetentionTask's snapshot filtering and delet… (elastic#44764) * Implement SnapshotRetentionTask's snapshot filtering and deletion This commit implements the snapshot filtering and deletion for `SnapshotRetentionTask`. Currently only the expire-after age is used for determining whether a snapshot is eligible for deletion. Relates to elastic#43663 * Fix deletes running on the wrong thread * Handle missing or null policy in snap metadata differently * Convert Tuple<String, List<SnapshotInfo>> to Map<String, List<SnapshotInfo>> * Use the `OriginSettingClient` to work with security, enhance logging * Prevent NPE in test by mocking Client * Allow empty/missing SLM retention configuration (elastic#45018) Semi-related to elastic#44465, this allows the `"retention"` configuration map to be missing. Relates to elastic#43663 * Add min_count and max_count as SLM retention predicates (elastic#44926) This adds the configuration options for `min_count` and `max_count` as well as the logic for determining whether a snapshot meets this criteria to SLM's retention feature. These options are optional and one, two, or all three can be specified in an SLM policy. Relates to elastic#43663 * Time-bound deletion of snapshots in retention delete function (elastic#45065) * Time-bound deletion of snapshots in retention delete function With a cluster that has a large number of snapshots, it's possible that snapshot deletion can take a very long time (especially since deletes currently have to happen in a serial fashion). To prevent snapshot deletion from taking forever in a cluster and blocking other operations, this commit adds a setting to allow configuring a maximum time to spend deletion snapshots during retention. This dynamic setting defaults to 1 hour and is best-effort, meaning that it doesn't hard stop a deletion at an hour mark, but ensures that once the time has passed, all subsequent deletions are deferred until the next retention cycle. Relates to elastic#43663 * Wow snapshots suuuure can take a long time. * Use a LongSupplier instead of actually sleeping * Remove TestLogging annotation * Remove rate limiting * Add SLM metrics gathering and endpoint (elastic#45362) * Add SLM metrics gathering and endpoint This commit adds the infrastructure to gather metrics about the different SLM actions that a cluster takes. These actions are stored in `SnapshotLifecycleStats` and perpetuated in cluster state. The stats stored include the number of snapshots taken, failed, deleted, the number of retention runs, as well as per-policy counts for snapshots taken, failed, and deleted. It also includes the amount of time spent deleting snapshots from SLM retention. This commit also adds an endpoint for retrieving all stats (further commits will expose this in the SLM get-policy API) that looks like: ``` GET /_slm/stats { "retention_runs" : 13, "retention_failed" : 0, "retention_timed_out" : 0, "retention_deletion_time" : "1.4s", "retention_deletion_time_millis" : 1404, "policy_metrics" : { "daily-snapshots2" : { "snapshots_taken" : 7, "snapshots_failed" : 0, "snapshots_deleted" : 6, "snapshot_deletion_failures" : 0 }, "daily-snapshots" : { "snapshots_taken" : 12, "snapshots_failed" : 0, "snapshots_deleted" : 12, "snapshot_deletion_failures" : 6 } }, "total_snapshots_taken" : 19, "total_snapshots_failed" : 0, "total_snapshots_deleted" : 18, "total_snapshot_deletion_failures" : 6 } ``` This does not yet include HLRC for this, as this commit is quite large on its own. That will be added in a subsequent commit. Relates to elastic#43663 * Version qualify serialization * Initialize counters outside constructor * Use computeIfAbsent instead of being too verbose * Move part of XContent generation into subclass * Fix REST action for master merge * Unused import * Record history of SLM retention actions (elastic#45513) This commit records the deletion of snapshots by the retention component of SLM into the SLM history index for the purposes of reviewing operations taken by SLM and alerting. * Retry SLM retention after currently running snapshot completes (elastic#45802) * Retry SLM retention after currently running snapshot completes This commit adds a ClusterStateObserver to wait until the currently running snapshot is complete before proceeding with snapshot deletion. SLM retention waits for the maximum allowed deletion time for the snapshot to complete, however, the waiting time is not factored into the limit on actual deletions. Relates to elastic#43663 * Increase timeout waiting for snapshot completion * Apply patch From https://github.com/original-brownbear/elasticsearch/commit/2374316f0d1912c9e1498bece195546a1dc60bce.patch * Rename test variables * [TEST] Be less strict for stats checking * Skip SLM retention if ILM is STOPPING or STOPPED (elastic#45869) This adds a check to ensure we take no action during SLM retention if ILM is currently stopped or in the process of stopping. Relates to elastic#43663 * Check all actions preventing snapshot delete during retention (elastic#45992) * Check all actions preventing snapshot delete during retention run Previously we only checked to see if a snapshot was currently running, but it turns out that more things can block snapshot deletion. This changes the check to be a check for: - a snapshot currently running - a deletion already in progress - a repo cleanup in progress - a restore currently running This was found by CI where a third party delete in a test caused SLM retention deletion to throw an exception. Relates to elastic#43663 * Add unit test for okayToDeleteSnapshots * Fix bug where SLM retention task would be scheduled on every node * Enhance test logging * Ignore if snapshot is already deleted * Missing import * Fix SnapshotRetentionServiceTests * Expose SLM policy stats in get SLM policy API (elastic#45989) This also adds support for the SLM stats endpoint to the high level rest client. Retrieving a policy now looks like: ```json { "daily-snapshots" : { "version": 1, "modified_date": "2019-04-23T01:30:00.000Z", "modified_date_millis": 1556048137314, "policy" : { "schedule": "0 30 1 * * ?", "name": "<daily-snap-{now/d}>", "repository": "my_repository", "config": { "indices": ["data-*", "important"], "ignore_unavailable": false, "include_global_state": false }, "retention": {} }, "stats": { "snapshots_taken": 0, "snapshots_failed": 0, "snapshots_deleted": 0, "snapshot_deletion_failures": 0 }, "next_execution": "2019-04-24T01:30:00.000Z", "next_execution_millis": 1556048160000 } } ``` Relates to elastic#43663 * Rewrite SnapshotLifecycleIT as as ESIntegTestCase (elastic#46356) * Rewrite SnapshotLifecycleIT as as ESIntegTestCase This commit splits `SnapshotLifecycleIT` into two different tests. `SnapshotLifecycleRestIT` which includes the tests that do not require slow repositories, and `SLMSnapshotBlockingIntegTests` which is now an integration test using `MockRepository` to simulate a snapshot being in progress. Relates to elastic#43663 Resolves elastic#46205 * Add error logging when exceptions are thrown
dakrone
added a commit
to dakrone/elasticsearch
that referenced
this pull request
Sep 9, 2019
SLM retention was merged in elastic#46407 and will be backported in elastic#46506. This disables BWC tests until both the backport and the version change in elastic#46509 are merged.
dakrone
added a commit
that referenced
this pull request
Sep 10, 2019
dakrone
added a commit
that referenced
this pull request
Sep 10, 2019
* Add retention to Snapshot Lifecycle Management (#46407) This commit adds retention to the existing Snapshot Lifecycle Management feature (#38461) as described in #43663. This allows a user to configure SLM to automatically delete older snapshots based on a number of criteria. An example policy would look like: ``` PUT /_slm/policy/snapshot-every-day { "schedule": "0 30 2 * * ?", "name": "<production-snap-{now/d}>", "repository": "my-s3-repository", "config": { "indices": ["foo-*", "important"] }, // Newly configured retention options "retention": { // Snapshots should be deleted after 14 days "expire_after": "14d", // Keep a maximum of thirty snapshots "max_count": 30, // Keep a minimum of the four most recent snapshots "min_count": 4 } } ``` SLM Retention is run on a scheduled configurable with the `slm.retention_schedule` setting, which supports cron expressions. Deletions are run for a configurable time bounded by the `slm.retention_duration` setting, which defaults to 1 hour. Included in this work is a new SLM stats API endpoint available through ``` json GET /_slm/stats ``` That returns statistics about snapshot taken and deleted, as well as successful retention runs, failures, and the time spent deleting snapshots. #45362 has more information as well as an example of the output. These stats are also included when retrieving SLM policies via the API. * Add base framework for snapshot retention (#43605) * Add base framework for snapshot retention This adds a basic `SnapshotRetentionService` and `SnapshotRetentionTask` to start as the basis for SLM's retention implementation. Relates to #38461 * Remove extraneous 'public' * Use a local var instead of reading class var repeatedly * Add SnapshotRetentionConfiguration for retention configuration (#43777) * Add SnapshotRetentionConfiguration for retention configuration This commit adds the `SnapshotRetentionConfiguration` class and its HLRC counterpart to encapsulate the configuration for SLM retention. Currently only a single parameter is supported as an example (we still need to discuss the different options we want to support and their names) to keep the size of the PR down. It also does not yet include version serialization checks since the original SLM branch has not yet been merged. Relates to #43663 * Fix REST tests * Fix more documentation * Use Objects.equals to avoid NPE * Put `randomSnapshotLifecyclePolicy` in only one place * Occasionally return retention with no configuration * Implement SnapshotRetentionTask's snapshot filtering and delet… (#44764) * Implement SnapshotRetentionTask's snapshot filtering and deletion This commit implements the snapshot filtering and deletion for `SnapshotRetentionTask`. Currently only the expire-after age is used for determining whether a snapshot is eligible for deletion. Relates to #43663 * Fix deletes running on the wrong thread * Handle missing or null policy in snap metadata differently * Convert Tuple<String, List<SnapshotInfo>> to Map<String, List<SnapshotInfo>> * Use the `OriginSettingClient` to work with security, enhance logging * Prevent NPE in test by mocking Client * Allow empty/missing SLM retention configuration (#45018) Semi-related to #44465, this allows the `"retention"` configuration map to be missing. Relates to #43663 * Add min_count and max_count as SLM retention predicates (#44926) This adds the configuration options for `min_count` and `max_count` as well as the logic for determining whether a snapshot meets this criteria to SLM's retention feature. These options are optional and one, two, or all three can be specified in an SLM policy. Relates to #43663 * Time-bound deletion of snapshots in retention delete function (#45065) * Time-bound deletion of snapshots in retention delete function With a cluster that has a large number of snapshots, it's possible that snapshot deletion can take a very long time (especially since deletes currently have to happen in a serial fashion). To prevent snapshot deletion from taking forever in a cluster and blocking other operations, this commit adds a setting to allow configuring a maximum time to spend deletion snapshots during retention. This dynamic setting defaults to 1 hour and is best-effort, meaning that it doesn't hard stop a deletion at an hour mark, but ensures that once the time has passed, all subsequent deletions are deferred until the next retention cycle. Relates to #43663 * Wow snapshots suuuure can take a long time. * Use a LongSupplier instead of actually sleeping * Remove TestLogging annotation * Remove rate limiting * Add SLM metrics gathering and endpoint (#45362) * Add SLM metrics gathering and endpoint This commit adds the infrastructure to gather metrics about the different SLM actions that a cluster takes. These actions are stored in `SnapshotLifecycleStats` and perpetuated in cluster state. The stats stored include the number of snapshots taken, failed, deleted, the number of retention runs, as well as per-policy counts for snapshots taken, failed, and deleted. It also includes the amount of time spent deleting snapshots from SLM retention. This commit also adds an endpoint for retrieving all stats (further commits will expose this in the SLM get-policy API) that looks like: ``` GET /_slm/stats { "retention_runs" : 13, "retention_failed" : 0, "retention_timed_out" : 0, "retention_deletion_time" : "1.4s", "retention_deletion_time_millis" : 1404, "policy_metrics" : { "daily-snapshots2" : { "snapshots_taken" : 7, "snapshots_failed" : 0, "snapshots_deleted" : 6, "snapshot_deletion_failures" : 0 }, "daily-snapshots" : { "snapshots_taken" : 12, "snapshots_failed" : 0, "snapshots_deleted" : 12, "snapshot_deletion_failures" : 6 } }, "total_snapshots_taken" : 19, "total_snapshots_failed" : 0, "total_snapshots_deleted" : 18, "total_snapshot_deletion_failures" : 6 } ``` This does not yet include HLRC for this, as this commit is quite large on its own. That will be added in a subsequent commit. Relates to #43663 * Version qualify serialization * Initialize counters outside constructor * Use computeIfAbsent instead of being too verbose * Move part of XContent generation into subclass * Fix REST action for master merge * Unused import * Record history of SLM retention actions (#45513) This commit records the deletion of snapshots by the retention component of SLM into the SLM history index for the purposes of reviewing operations taken by SLM and alerting. * Retry SLM retention after currently running snapshot completes (#45802) * Retry SLM retention after currently running snapshot completes This commit adds a ClusterStateObserver to wait until the currently running snapshot is complete before proceeding with snapshot deletion. SLM retention waits for the maximum allowed deletion time for the snapshot to complete, however, the waiting time is not factored into the limit on actual deletions. Relates to #43663 * Increase timeout waiting for snapshot completion * Apply patch From https://github.com/original-brownbear/elasticsearch/commit/2374316f0d1912c9e1498bece195546a1dc60bce.patch * Rename test variables * [TEST] Be less strict for stats checking * Skip SLM retention if ILM is STOPPING or STOPPED (#45869) This adds a check to ensure we take no action during SLM retention if ILM is currently stopped or in the process of stopping. Relates to #43663 * Check all actions preventing snapshot delete during retention (#45992) * Check all actions preventing snapshot delete during retention run Previously we only checked to see if a snapshot was currently running, but it turns out that more things can block snapshot deletion. This changes the check to be a check for: - a snapshot currently running - a deletion already in progress - a repo cleanup in progress - a restore currently running This was found by CI where a third party delete in a test caused SLM retention deletion to throw an exception. Relates to #43663 * Add unit test for okayToDeleteSnapshots * Fix bug where SLM retention task would be scheduled on every node * Enhance test logging * Ignore if snapshot is already deleted * Missing import * Fix SnapshotRetentionServiceTests * Expose SLM policy stats in get SLM policy API (#45989) This also adds support for the SLM stats endpoint to the high level rest client. Retrieving a policy now looks like: ```json { "daily-snapshots" : { "version": 1, "modified_date": "2019-04-23T01:30:00.000Z", "modified_date_millis": 1556048137314, "policy" : { "schedule": "0 30 1 * * ?", "name": "<daily-snap-{now/d}>", "repository": "my_repository", "config": { "indices": ["data-*", "important"], "ignore_unavailable": false, "include_global_state": false }, "retention": {} }, "stats": { "snapshots_taken": 0, "snapshots_failed": 0, "snapshots_deleted": 0, "snapshot_deletion_failures": 0 }, "next_execution": "2019-04-24T01:30:00.000Z", "next_execution_millis": 1556048160000 } } ``` Relates to #43663 * Rewrite SnapshotLifecycleIT as as ESIntegTestCase (#46356) * Rewrite SnapshotLifecycleIT as as ESIntegTestCase This commit splits `SnapshotLifecycleIT` into two different tests. `SnapshotLifecycleRestIT` which includes the tests that do not require slow repositories, and `SLMSnapshotBlockingIntegTests` which is now an integration test using `MockRepository` to simulate a snapshot being in progress. Relates to #43663 Resolves #46205 * Add error logging when exceptions are thrown * Update serialization versions * Fix type inference * Use non-Cancellable HLRC return value * Fix Client mocking in test * Fix SLMSnapshotBlockingIntegTests for 7.x branch * Update SnapshotRetentionTask for non-multi-repo snapshot retrieval * Add serialization guards for SnapshotLifecyclePolicy
24 tasks
Sign up for free
to join this conversation on GitHub.
Already have an account?
Sign in to comment
Add this suggestion to a batch that can be applied as a single commit.
This suggestion is invalid because no changes were made to the code.
Suggestions cannot be applied while the pull request is closed.
Suggestions cannot be applied while viewing a subset of changes.
Only one suggestion per line can be applied in a batch.
Add this suggestion to a batch that can be applied as a single commit.
Applying suggestions on deleted lines is not supported.
You must change the existing code in this line in order to create a valid suggestion.
Outdated suggestions cannot be applied.
This suggestion has been applied or marked resolved.
Suggestions cannot be applied from pending reviews.
Suggestions cannot be applied on multi-line comments.
Suggestions cannot be applied while the pull request is queued to merge.
Suggestion cannot be applied right now. Please check back later.
This commit adds retention to the existing Snapshot Lifecycle Management feature (#38461) as described in #43663. This allows a user to configure SLM to automatically delete older snapshots based on a number of criteria.
An example policy would look like:
SLM Retention is run on a scheduled configurable with the
slm.retention_schedulesetting, which supports cron expressions. Deletions are run for a configurable time bounded by theslm.retention_durationsetting, which defaults to 1 hour.Included in this work is a new SLM stats API endpoint available through
GET /_slm/statsThat returns statistics about snapshot taken and deleted, as well as successful retention runs, failures, and the time spent deleting snapshots. #45362 has more information as well as an example of the output. These stats are also included when retrieving SLM policies via the API.