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add embedded data section

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Oskar Thoren 2019-09-30 12:49:58 +08:00
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remote_log/remote_log_spec.md
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@ -1,6 +1,6 @@
# Remote log specification
> Version: 0.0.9 (Draft)
> Version: 0.0.10 (Draft)
>
> Authors: Oskar Thorén oskar@status.im, Dean Eigenmann dean@status.im
@ -155,10 +155,8 @@ modes:
2. Normal sized page with CAS mapping
3. "Linked list" mode - minimally sized page with CAS mapping
<!-- TODO: Elaborate on continuum from linked list to fully replicated log -->
<!-- TODO: Elaborate on how to indicate which CAS is used, a la multiaddr -->
**Data format:**
```
@ -171,8 +169,29 @@ modes:
Here the upper section indicates a list of ordered pairs, and the lower section
contains the address for the next page chunk. `H1` is the native hash function,
and `H2` is the one used by the CAS.
and `H2` is the one used by the CAS. The numbers corresponds to the messages.
**Embedded data:**
A remote log MAY also choose to embed the wire payloads that corresponds to the
native hash. This bypasses the need for a dedicated CAS and additional
round-trips, with a trade-off in bandwidth usage.
```
| H1_3 | | C_3 |
| H1_2 | | C_2 |
| H1_1 | | C_1 |
| -------------|
| next_page |
```
Here `C` stands for the content that would be stored at the CAS.
Both patterns can be used in parallel, e,g. by storing the last `k` messages
directly and use CAS pointers for the rest. Together with the `next_page` page
semantics, this gives users flexibility in terms of bandwidth and
latency/indirection, all the way from a simple linked list to a fully replicated
log. The latter is useful for things like backups on durable storage.
### Next page semantics