[wp-trac] [WordPress Trac] #30937: Add Customizer state persistence in changesets (formerly “transactions”)

Mon Oct 17 05:15:05 UTC 2016

#30937: Add Customizer state persistence in changesets (formerly “transactions”)
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 Reporter:  westonruter                          |       Owner:
     Type:  feature request                      |  westonruter
 Priority:  high                                 |      Status:  assigned
Component:  Customize                            |   Milestone:  4.7
 Severity:  normal                               |     Version:
 Keywords:  has-patch needs-testing needs-unit-  |  Resolution:
  tests                                          |     Focuses:
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Comment (by westonruter):

 On Friday I realized a serious performance problem with how changesets
 were implemented. Which is now obvious to me now, the approach of trying
 to update the `customize_changeset` post every time (debounced 250ms) that
 a setting is updated will hammer the MySQL database with writes. DB writes
 are very slow compared with reads. What's even worse is that the HTTP
 request being made to update the changeset was blocking both the full
 refresh request and the selective refresh request, resulting in a
 customizer preview that was at least twice as slow.

 The solution to the performance problem is to return to using a `POST`
 request for previewing changes when the changeset is not yet updated in
 the DB. Instead of doing an Ajax `POST` request and then using
 `document.write()` into an iframe, the patch instead creates a temporary
 form and sets the `target` window for the form to be iframe. This ensures
 that the document in the iframe will run in the context of the expected
 URL, and it will also allow us to amend the customized state with any
 unsaved setting values that have yet to be persisted into the changeset.
 So also with this change, the changeset is now auto-saved at the
 `AUTOSAVE_INTERVAL` and also whenever a `blur` event is triggered on the
 customizer window.

 Full writeup on the problem and solution can be seen here:
 https://github.com/xwp/wordpress-develop/issues/170

 These changes and others made over the weekend: https://github.com/xwp
 /wordpress-develop/pull/161/files/c09a0eb..0753db3

 * [https://github.com/xwp/wordpress-develop/pull/161/commits/27ae83c
 27ae83c] Eliminate updating changeset with every change in favor of
 autosave polling
 * [https://github.com/xwp/wordpress-develop/pull/161/commits/b4ff52c
 b4ff52c] Remove marking of changeset-saved settings as clean, missed in
 58b31cf
 * [https://github.com/xwp/wordpress-develop/pull/161/commits/1c82e40
 1c82e40] Only increment setting revision for added setting if it is
 initially dirty
 * [https://github.com/xwp/wordpress-develop/pull/161/commits/0be8eca
 0be8eca] Introduce wp.customize.dirtyValues method; replace
 excludeCustomized with excludeCustomizedSaved option for previewer.query()
 * [https://github.com/xwp/wordpress-develop/pull/161/commits/5f5056d
 5f5056d] Short-circuit changeset update request if there are no pending
 changes
 * [https://github.com/xwp/wordpress-develop/pull/161/commits/2fc8ec8
 2fc8ec8] Populate iframe window via form submitting post request with
 unsaved values instead of just src to URL with changeset UUID
 * [https://github.com/xwp/wordpress-develop/pull/161/commits/2cb33f3
 2cb33f3] Clarify that PreviewFrame.uuid() does not return an actual UUID
 * [https://github.com/xwp/wordpress-develop/pull/161/commits/7b94257
 7b94257] Remove obsolete reference to Previewer.request
 * [https://github.com/xwp/wordpress-develop/pull/161/commits/8f0bede
 8f0bede] Only update lastSavedRevision when changeset update successful
 * [https://github.com/xwp/wordpress-develop/pull/161/commits/469ffed
 469ffed] Vastly simplify requestChangesetUpdate now that debouncing and
 request locking removed
 * [https://github.com/xwp/wordpress-develop/pull/161/commits/7f97497
 7f97497] Restore sending settingValidities and _dirty in full refresh
 * [https://github.com/xwp/wordpress-develop/pull/161/commits/838e415
 838e415] Request changeset update when customizer window hidden or before
 unloaded
 * [https://github.com/xwp/wordpress-develop/pull/161/commits/13b89d4
 13b89d4] Remove provision for plugins including customize_changeset on
 export screen for now
 * [https://github.com/xwp/wordpress-develop/pull/161/commits/86eec4b
 86eec4b] Fix _wp_scripts_maybe_doing_it_wrong in
 WP_Customize_Manager::wp_die()
 * [https://github.com/xwp/wordpress-develop/pull/161/commits/1794d2f
 1794d2f] Use GET and POST query vars instead of REQUEST when bootstrapping
 customizer
 * [https://github.com/xwp/wordpress-develop/pull/161/commits/5d5a529
 5d5a529] Rewrite Ajax GET requests to be POST requests with customized
 state data included
 * [https://github.com/xwp/wordpress-develop/pull/161/commits/21f6bf3
 21f6bf3] Use AUTOSAVE_INTERVAL as changesetAutoSave
 * [https://github.com/xwp/wordpress-develop/pull/161/commits/ae5a980
 ae5a980] Add data-src attribute to iframe to facilitate debugging
 * [https://github.com/xwp/wordpress-develop/pull/161/commits/70c52ce
 70c52ce] Add data-src attribute to iframe to facilitate debugging
 * [https://github.com/xwp/wordpress-develop/pull/161/commits/8b3c3df
 8b3c3df] Ensure that changeset is updated prior to theme preview switch;
 eliminate replaceState requirement and AYS dialog
 * [https://github.com/xwp/wordpress-develop/pull/161/commits/f53f8f7
 f53f8f7] Use window blur instead of page visibility hidden to trigger save
 * [https://github.com/xwp/wordpress-develop/pull/161/commits/4df7928
 4df7928] Prevent background changeset update if another is currently in
 progress
 * [https://github.com/xwp/wordpress-develop/pull/161/commits/a6cd0f2
 a6cd0f2] Remove unnecessary stateQueryParams setting
 * [https://github.com/xwp/wordpress-develop/pull/161/commits/63e16e2
 63e16e2] Clarify when a customize_save request is transactional and allows
 revisions
 * [https://github.com/xwp/wordpress-develop/pull/161/commits/7e5fa46
 7e5fa46] Remove todos
 * [https://github.com/xwp/wordpress-develop/pull/161/commits/9273c08
 9273c08] Add object caching for changeset UUID to post ID lookup
 * [https://github.com/xwp/wordpress-develop/pull/161/commits/ea7d3e9
 ea7d3e9] Load preview via iframe[src] if no unsaved dirty changes;
 otherwise, use form post request into window
 * [https://github.com/xwp/wordpress-develop/pull/161/commits/f222717
 f222717] Skip incrementing processing state if requestChangesetUpdate will
 short-circuit
 * [https://github.com/xwp/wordpress-develop/pull/161/commits/f265835
 f265835] Prevent date from being cleared in wp_update_post call
 * [https://github.com/xwp/wordpress-develop/pull/161/commits/cf91851
 cf91851] Allow date formats accepted by strtotime in customize_save
 requests
 * [https://github.com/xwp/wordpress-develop/pull/161/commits/9d615b8
 9d615b8] Add link to start new customizer session when wp_die'd due to
 already-published changeset
 * [https://github.com/xwp/wordpress-develop/pull/161/commits/9ab8c26
 9ab8c26] Ensure save & publish button is disabled immediately once there
 are unsaved changes
 * [https://github.com/xwp/wordpress-develop/pull/161/commits/3cc1ea8
 3cc1ea8] Break up methods to improve testability
 * [https://github.com/xwp/wordpress-develop/pull/161/commits/0753db3
 0753db3] Ensure changeset_status is returned as publish when sending
 future with non-future date

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Ticket URL: <https://core.trac.wordpress.org/ticket/30937#comment:75>
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