…erer

…ng it with webpack import/require

…e fetch to not create additional request, with any `cache` or `mode` configuration

… - results in smaller app bundle especially with large ammount of pages

[WIP][v2] build updates

Instead only push results out if the data is for a path that's currently
being viewed in a client.

[v2] Enable cached query results to be loaded

…f path already has query in flight

…cessing (#4785)

* Don't emit new file node until previous is finished processing

This is an experiment to use
[xstate](http://davidkpiano.github.io/xstate/docs/#/) to setup state
machines to better handle complex state changes as we sometimes have.

Ideally this happens in core and then gatsby-source-filesystem
just has a simple queue and emits a new file node every time
the system returns to idle.

In a future refactor we'll do that plus refactor other parts of core
that should be handled in a state machine e.g. pages-query-runner.js

This PR also reinforced the need for us to implement
[tracing](https://github.com/jaegertracing/jaeger) in core / plugins
as that'd make it far far easier to understand what's happening and
when.

* Document state machine and remove extraneous Chokidar states

* Remove console.log

* Don't emit new file node until previous is finished processing

This is an experiment to use
[xstate](http://davidkpiano.github.io/xstate/docs/#/) to setup state
machines to better handle complex state changes as we sometimes have.

Ideally this happens in core and then gatsby-source-filesystem
just has a simple queue and emits a new file node every time
the system returns to idle.

In a future refactor we'll do that plus refactor other parts of core
that should be handled in a state machine e.g. pages-query-runner.js

This PR also reinforced the need for us to implement
[tracing](https://github.com/jaegertracing/jaeger) in core / plugins
as that'd make it far far easier to understand what's happening and
when.

* Document state machine and remove extraneous Chokidar states

* Remove console.log

* Only log file events if we're past bootstrap

* prevent adding duplicate redirects

* don't write new `redirects.json` if redirects didn't change

prevents webpack recompilation on data change

* dont emit results for layouts

* [develop] store query results in memory, read json data from file only if we don't have it stored yet (we didn't run this query, but results are cached)

Query running is sadly not very ludicrous right now on gatsbyjs.org —
not sure why — each markdown file change causes ~20 queries to run but
even with prioritizing the active page's query, it's still ~2 seconds
before the page updates.

This sort of thing will be much easier to debug with tracing support.