[Sync] Add a doc about the SharedModelTypeProcessor.

[Sync] Add a doc about the SharedModelTypeProcessor.

Just a brain-dump of my current understanding of how SMTP state works.

BUG=

Review-Url: https://codereview.chromium.org/2672123002
Cr-Commit-Position: refs/heads/master@{#448130}
Committed: https://chromium.googlesource.com/chromium/src/+/da6bfa38a01d5bda51eb7ae4f5382726dd4ac668

[maxbogue, 2017-02-03 21:41:05]

maxbogue@chromium.org changed reviewers:
+ skym@chromium.org

[maxbogue, 2017-02-03 21:41:05]

Sky, PTAL!

[skym, 2017-02-03 21:53:28]

lgtm

https://codereview.chromium.org/2672123002/diff/20001/components/sync/model_i...
File components/sync/model_impl/shared_model_type_processor.h (right):

https://codereview.chromium.org/2672123002/diff/20001/components/sync/model_i...
components/sync/model_impl/shared_model_type_processor.h:143:
/////////////////////
fancy

https://codereview.chromium.org/2672123002/diff/20001/docs/sync/uss/shared_mo...
File docs/sync/uss/shared_model_type_processor.md (right):

https://codereview.chromium.org/2672123002/diff/20001/docs/sync/uss/shared_mo...
docs/sync/uss/shared_model_type_processor.md:3: The
[`SharedModelTypeProcessor`][SMTP] is a crucial piece of the USS codepath.
This paragraph is really really good. Give so much context and explanation of
how it interacts with neighbors.

https://codereview.chromium.org/2672123002/diff/20001/docs/sync/uss/shared_mo...
docs/sync/uss/shared_model_type_processor.md:88: *   Once the processor receives
its connection to the worker, data is being
I found this area a little confusing. We are still tracking metadata when we're
`SYNCING` and IsTrackingMetadata() will return true.

https://codereview.chromium.org/2672123002/diff/20001/docs/sync/uss/shared_mo...
docs/sync/uss/shared_model_type_processor.md:93: The
[`ProcessorEntityTracker`][PET] tracks the state of individual entities for
Would be good to add a little here, emphasizing that some metadata is kept
around indefinitely. This is the main overhead of the processor, and why we
choose do to things this way.

[Patrick Noland, 2017-02-03 21:59:01]

pnoland@chromium.org changed reviewers:
+ pnoland@chromium.org

[Patrick Noland, 2017-02-03 21:59:02]

Please excuse the driveby

https://codereview.chromium.org/2672123002/diff/20001/docs/sync/uss/shared_mo...
File docs/sync/uss/shared_model_type_processor.md (right):

https://codereview.chromium.org/2672123002/diff/20001/docs/sync/uss/shared_mo...
docs/sync/uss/shared_model_type_processor.md:28: The processor sits between the
model brigde and the sync engine. It has
[typo] bridge

https://codereview.chromium.org/2672123002/diff/20001/docs/sync/uss/shared_mo...
docs/sync/uss/shared_model_type_processor.md:81: *   `Put` and `Delete` calls
are not allowed in this state.
What are the consequences of calling Put and Delete in this state? DCHECK,
no-op, etc.

https://codereview.chromium.org/2672123002/diff/20001/docs/sync/uss/shared_mo...
docs/sync/uss/shared_model_type_processor.md:82: *   `TRACKING` or
`NOT_TRACKING`
This is a bit hard to follow, maybe these two should just each get their own
description?

[maxbogue, 2017-02-03 23:30:47]

The CQ bit was checked by maxbogue@chromium.org to run a CQ dry run

[maxbogue, 2017-02-03 23:30:55]

https://codereview.chromium.org/2672123002/diff/20001/components/sync/model_i...
File components/sync/model_impl/shared_model_type_processor.h (right):

https://codereview.chromium.org/2672123002/diff/20001/components/sync/model_i...
components/sync/model_impl/shared_model_type_processor.h:143:
/////////////////////
On 2017/02/03 21:53:27, skym wrote:
> fancy

so fancy

https://codereview.chromium.org/2672123002/diff/20001/docs/sync/uss/shared_mo...
File docs/sync/uss/shared_model_type_processor.md (right):

https://codereview.chromium.org/2672123002/diff/20001/docs/sync/uss/shared_mo...
docs/sync/uss/shared_model_type_processor.md:3: The
[`SharedModelTypeProcessor`][SMTP] is a crucial piece of the USS codepath.
On 2017/02/03 21:53:27, skym wrote:
> This paragraph is really really good. Give so much context and explanation of
> how it interacts with neighbors.

Thanks!

https://codereview.chromium.org/2672123002/diff/20001/docs/sync/uss/shared_mo...
docs/sync/uss/shared_model_type_processor.md:28: The processor sits between the
model brigde and the sync engine. It has
On 2017/02/03 21:59:02, Patrick Noland wrote:
> [typo] bridge

Done.

https://codereview.chromium.org/2672123002/diff/20001/docs/sync/uss/shared_mo...
docs/sync/uss/shared_model_type_processor.md:81: *   `Put` and `Delete` calls
are not allowed in this state.
On 2017/02/03 21:59:02, Patrick Noland wrote:
> What are the consequences of calling Put and Delete in this state? DCHECK,
> no-op, etc.

Done.

https://codereview.chromium.org/2672123002/diff/20001/docs/sync/uss/shared_mo...
docs/sync/uss/shared_model_type_processor.md:82: *   `TRACKING` or
`NOT_TRACKING`
On 2017/02/03 21:59:02, Patrick Noland wrote:
> This is a bit hard to follow, maybe these two should just each get their own
> description?

Done.

https://codereview.chromium.org/2672123002/diff/20001/docs/sync/uss/shared_mo...
docs/sync/uss/shared_model_type_processor.md:88: *   Once the processor receives
its connection to the worker, data is being
On 2017/02/03 21:53:27, skym wrote:
> I found this area a little confusing. We are still tracking metadata when
we're
> `SYNCING` and IsTrackingMetadata() will return true.

Done.

https://codereview.chromium.org/2672123002/diff/20001/docs/sync/uss/shared_mo...
docs/sync/uss/shared_model_type_processor.md:93: The
[`ProcessorEntityTracker`][PET] tracks the state of individual entities for
On 2017/02/03 21:53:27, skym wrote:
> Would be good to add a little here, emphasizing that some metadata is kept
> around indefinitely. This is the main overhead of the processor, and why we
> choose do to things this way.

Done.

[commit-bot: I haz the power, 2017-02-03 23:31:28]

Dry run: CQ is trying da patch. Follow status at
 
https://chromium-cq-status.appspot.com/v2/patch-status/codereview.chromium.or...

[maxbogue, 2017-02-03 23:59:34]

The CQ bit was unchecked by maxbogue@chromium.org

[maxbogue, 2017-02-03 23:59:37]

The CQ bit was checked by maxbogue@chromium.org

[maxbogue, 2017-02-03 23:59:37]

The patchset sent to the CQ was uploaded after l-g-t-m from skym@chromium.org
Link to the patchset: https://codereview.chromium.org/2672123002/#ps40001
(title: "Address comments.")

[commit-bot: I haz the power, 2017-02-04 00:00:01]

CQ is trying da patch. Follow status at
 
https://chromium-cq-status.appspot.com/v2/patch-status/codereview.chromium.or...

[commit-bot: I haz the power, 2017-02-04 00:51:15]

CQ is committing da patch.

Bot data: {"patchset_id": 40001, "attempt_start_ts": 1486166377381260,
"parent_rev": "3c7d8329f2e7d378d62b907db0095fa80835c57b", "commit_rev":
"da6bfa38a01d5bda51eb7ae4f5382726dd4ac668"}

[commit-bot: I haz the power, 2017-02-04 00:51:47]

Description was changed from

==========
[Sync] Add a doc about the SharedModelTypeProcessor.

Just a brain-dump of my current understanding of how SMTP state works.

BUG=
==========

to

==========
[Sync] Add a doc about the SharedModelTypeProcessor.

Just a brain-dump of my current understanding of how SMTP state works.

BUG=

Review-Url: https://codereview.chromium.org/2672123002
Cr-Commit-Position: refs/heads/master@{#448130}
Committed:
https://chromium.googlesource.com/chromium/src/+/da6bfa38a01d5bda51eb7ae4f538...
==========

[commit-bot: I haz the power, 2017-02-04 00:51:48]

Committed patchset #3 (id:40001) as
https://chromium.googlesource.com/chromium/src/+/da6bfa38a01d5bda51eb7ae4f538...