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etcdctlv3: interactive_v3 watch command update

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sharat 2016-09-26 23:33:45 +05:30
parent e1efdd591e
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Documentation/dev-guide/interacting_v3.md
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@ -227,22 +227,65 @@ Here is the command to watch on key `foo`:
```bash
$ etcdctl watch foo
# in another terminal: etcdctl put foo bar
PUT
foo
bar
```
Here is the command to watch on key `foo` in hex format:
```bash
$ etcdctl watch foo --hex
# in another terminal: etcdctl put foo bar
PUT
\x66\x6f\x6f # Key
\x62\x61\x72 # Value
```
Here is the command to watch on a range key from `foo` to `foo9`:
```bash
$ etcdctl watch foo foo9
# in another terminal: etcdctl put foo bar
PUT
foo
bar
# in another terminal: etcdctl put foo1 bar1
PUT
foo1
bar1
```
Here is the command to watch on keys having prefix `foo`:
```bash
$ etcdctl watch --prefix foo
# in another terminal: etcdctl put foo bar
PUT
foo
bar
# in another terminal: etcdctl put fooz1 barz1
PUT
fooz1
barz1
```
Here is the command to watch on multiple keys `foo` and `zoo`:
```bash
$ etcdctl watch -i
$ watch foo
$ watch zoo
# in another terminal: etcdctl put foo bar
PUT
foo
bar
# in another terminal: etcdctl put zoo val
PUT
zoo
val
```
## Watch historical changes of keys
Applications may want to watch for historical changes of keys in etcd. For example, an application may wish to receive all the modifications of a key; if the application stays connected to etcd, then `watch` is good enough. However, if the application or etcd fails, a change may happen during the failure, and the application will not receive the update in real time. To guarantee the update is delivered, the application must be able to watch for historical changes to keys. To do this, an application can specify a historical revision on a watch, just like reading past version of keys.
@ -250,10 +293,14 @@ Applications may want to watch for historical changes of keys in etcd. For examp
Suppose we finished the following sequence of operations:
```bash
etcdctl put foo bar # revision = 2
etcdctl put foo1 bar1 # revision = 3
etcdctl put foo bar_new # revision = 4
etcdctl put foo1 bar1_new # revision = 5
$ etcdctl put foo bar # revision = 2
OK
$ etcdctl put foo1 bar1 # revision = 3
OK
$ etcdctl put foo bar_new # revision = 4
OK
$ etcdctl put foo1 bar1_new # revision = 5
OK
```
Here is an example to watch the historical changes:
@ -267,7 +314,9 @@ bar
PUT
foo
bar_new
```
```bash
# watch for changes on key `foo` since revision 3
$ etcdctl watch --rev=3 foo
PUT
@ -275,6 +324,19 @@ foo
bar_new
```
Here is an example to watch only from the last historical change:
```bash
# watch for changes on key `foo` and return last revision value along with modified value
$ etcdctl watch --prev-kv foo
# in another terminal: etcdctl put foo bar_latest
PUT
foo # key
bar_new # last value of foo key before modification
foo # key
bar_latest # value of foo key after modification
```
## Compacted revisions
As we mentioned, etcd keeps revisions so that applications can read past versions of keys. However, to avoid accumulating an unbounded amount of history, it is important to compact past revisions. After compacting, etcd removes historical revisions, releasing resources for future use. All superseded data with revisions before the compacted revision will be unavailable.