Documentation/op-guide: document compactor change

Signed-off-by: Gyuho Lee <[email protected]>

Documentation/op-guide/maintenance.md

@@ -12,6 +12,22 @@ Since etcd keeps an exact history of its keyspace, this history should be period
 
 The keyspace can be compacted automatically with `etcd`'s time windowed history retention policy, or manually with `etcdctl`. The `etcdctl` method provides fine-grained control over the compacting process whereas automatic compacting fits applications that only need key history for some length of time.
 
+An `etcdctl` initiated compaction works as follows:
+
+```sh
+# compact up to revision 3
+$ etcdctl compact 3
+```
+
+Revisions prior to the compaction revision become inaccessible:
+
+```sh
+$ etcdctl get --rev=2 somekey
+Error:  rpc error: code = 11 desc = etcdserver: mvcc: required revision has been compacted
+```
+
+## History compaction: `--auto-compaction`
+
 `etcd` can be set to automatically compact the keyspace with the `--auto-compaction` option with a period of hours:
 
 ```sh
@@ -21,9 +37,11 @@ $ etcd --auto-compaction-retention=1
 
 [v3.0.0](https://github.com/coreos/etcd/blob/master/CHANGELOG-3.0.md) and [v3.1.0](https://github.com/coreos/etcd/blob/master/CHANGELOG-3.1.md) with `--auto-compaction-retention=10` run periodic compaction on v3 key-value store for every 10-hour. Compactor only supports periodic compaction. Compactor records latest revisions every 5-minute, until it reaches the first compaction period (e.g. 10-hour). In order to retain key-value history of last compaction period, it uses the last revision that was fetched before compaction period, from the revision records that were collected every 5-minute. When `--auto-compaction-retention=10`, compactor uses revision 100 for compact revision where revision 100 is the latest revision fetched from 10 hours ago. If compaction succeeds or requested revision has already been compacted, it resets period timer and starts over with new historical revision records (e.g. restart revision collect and compact for the next 10-hour period). If compaction fails, it retries in 5 minutes.
 
-[v3.2.0](https://github.com/coreos/etcd/blob/master/CHANGELOG-3.2.md) compactor runs [every hour](https://github.com/coreos/etcd/pull/7875). Compactor only supports periodic compaction. Compactor continues to record latest revisions every 5-minute. For every hour, it uses the last revision that was fetched before compaction period, from the revision records that were collected every 5-minute. That is, for every hour, compactor discards historical data created before compaction period. The retention window of compaction period moves to next hour. For instance, when hourly writes are about 100 and `--auto-compaction-retention=10`, v3.1 compacts revision 1000, 2000, and 3000 for every 10-hour, while v3.2 compacts revision 1000, 1100, and 1200 for every 1-hour. If compaction succeeds or requested revision has already been compacted, it resets period timer and removes used compacted revision from historical revision records (e.g. start next revision collect and compaction from previously collected revisions). If compaction fails, it retries in 5 minutes.
+[v3.2.0](https://github.com/coreos/etcd/blob/master/CHANGELOG-3.2.md) compactor runs [every hour](https://github.com/coreos/etcd/pull/7875). Compactor only supports periodic compaction. Compactor continues to record latest revisions every 5-minute. For every hour, it uses the last revision that was fetched before compaction period, from the revision records that were collected every 5-minute. That is, for every hour, compactor discards historical data created before compaction period. The retention window of compaction period moves to next hour. For instance, when hourly writes are 100 and `--auto-compaction-retention=10`, v3.1 compacts revision 1000, 2000, and 3000 for every 10-hour, while v3.2.x, v3.3.0, v3.3.1, and v3.3.2 compact revision 1000, 1100, and 1200 for every 1-hour. If compaction succeeds or requested revision has already been compacted, it resets period timer and removes used compacted revision from historical revision records (e.g. start next revision collect and compaction from previously collected revisions). If compaction fails, it retries in 5 minutes.
 
-[v3.3.0](https://github.com/coreos/etcd/blob/master/CHANGELOG-3.3.md) periodic compactor keeps recording latest revisions for every 1/10 of given compaction period (e.g. 1-hour when `--auto-compaction-mode=periodic --auto-compaction-retention=10h`). For every 1/10 of given compaction period, compactor uses the last revision that was fetched before compaction period, to discard historical data. The retention window of compaction period moves for every 1/10 of given compaction period. For instance, when hourly writes are about 100 and `--auto-compaction-retention=10`, v3.1 compacts revision 1000, 2000, and 3000 for every 10-hour, while v3.2 and v3.3 compacts revision 1000, 1100, and 1200 for every 1-hour. Futhermore, when writes per minute are about 1000, v3.3 with `--auto-compaction-mode=periodic --auto-compaction-retention=30m` can compact revision 30000, 33000, and 36000, for every 3-minute with more finer granularity. When `--auto-compaction-retention=10h`, etcd first waits 10-hour for the first compaction, and then does compaction every hour (1/10 of 10-hour) afterwards like this:
+In [v3.3.0](https://github.com/coreos/etcd/blob/master/CHANGELOG-3.3.md), [v3.3.1](https://github.com/coreos/etcd/blob/master/CHANGELOG-3.3.md), and [v3.3.2](https://github.com/coreos/etcd/blob/master/CHANGELOG-3.3.md), `--auto-compaction-mode=revision --auto-compaction-retention=1000` automatically `Compact` on `"latest revision" - 1000` every 5-minute (when latest revision is 30000, compact on revision 29000). For instance, `--auto-compaction-mode=periodic --auto-compaction-retention=72h` automatically `Compact` with 72-hour retention windown, for every 7.2-hour. For instance, `--auto-compaction-mode=periodic --auto-compaction-retention=30m` automatically `Compact` with 30-minute retention windown, for every 3-minute. Periodic compactor continues to record latest revisions for every 1/10 of given compaction period (e.g. 1-hour when `--auto-compaction-mode=periodic --auto-compaction-retention=10h`). For every 1/10 of given compaction period, compactor uses the last revision that was fetched before compaction period, to discard historical data. The retention window of compaction period moves for every 1/10 of given compaction period. For instance, when hourly writes are 100 and `--auto-compaction-retention=10`, v3.1 compacts revision 1000, 2000, and 3000 for every 10-hour, while v3.2.x, v3.3.0, v3.3.1, and v3.3.2 compact revision 1000, 1100, and 1200 for every 1-hour. Futhermore, when writes per minute are 1000, v3.3.0, v3.3.1, and v3.3.2 with `--auto-compaction-mode=periodic --auto-compaction-retention=30m` compact revision 30000, 33000, and 36000, for every 3-minute with more finer granularity.
+
+When `--auto-compaction-retention=10h`, etcd first waits 10-hour for the first compaction, and then does compaction every hour (1/10 of 10-hour) afterwards like this:
 
 ```
 0Hr  (rev = 1)
@@ -39,19 +57,7 @@ $ etcd --auto-compaction-retention=1
 
 Whether compaction succeeds or not, this process repeats for every 1/10 of given compaction period. If compaction succeeds, it just removes compacted revision from historical revision records.
 
-An `etcdctl` initiated compaction works as follows:
-
-```sh
-# compact up to revision 3
-$ etcdctl compact 3
-```
-
-Revisions prior to the compaction revision become inaccessible:
-
-```sh
-$ etcdctl get --rev=2 somekey
-Error:  rpc error: code = 11 desc = etcdserver: mvcc: required revision has been compacted
-```
+In [v3.3.3](https://github.com/coreos/etcd/blob/master/CHANGELOG-3.3.md), `--auto-compaction-mode=revision --auto-compaction-retention=1000` automatically `Compact` on `"latest revision" - 1000` every 5-minute (when latest revision is 30000, compact on revision 29000). Previously, `--auto-compaction-mode=periodic --auto-compaction-retention=72h` automatically `Compact` with 72-hour retention windown for every 7.2-hour.  **Now, `Compact` happens, for every 1-hour but still with 72-hour retention window.** Previously, `--auto-compaction-mode=periodic --auto-compaction-retention=30m` automatically `Compact` with 30-minute retention windown for every 3-minute. **Now, `Compact` happens, for every 30-minute but still with 30-minute retention window.** Periodic compactor keeps recording latest revisions for every compaction period when given period is less than 1-hour, or for every 1-hour when given compaction period is greater than 1-hour (e.g. 1-hour when `--auto-compaction-mode=periodic --auto-compaction-retention=24h`). For every compaction period or 1-hour, compactor uses the last revision that was fetched before compaction period, to discard historical data. The retention window of compaction period moves for every given compaction period or hour. For instance, when hourly writes are 100 and `--auto-compaction-mode=periodic --auto-compaction-retention=24h`, `v3.2.x`, `v3.3.0`, `v3.3.1`, and `v3.3.2` compact revision 2400, 2640, and 2880 for every 2.4-hour, while `v3.3.3` *or later* compacts revision 2400, 2500, 2600 for every 1-hour. Futhermore, when `--auto-compaction-mode=periodic --auto-compaction-retention=30m` and writes per minute are about 1000, `v3.3.0`, `v3.3.1`, and `v3.3.2` compact revision 30000, 33000, and 36000, for every 3-minute, while `v3.3.3` *or later* compacts revision 30000, 60000, and 90000, for every 30-minute.
 
 ## Defragmentation