[wp-trac] [WordPress Trac] #61343: Improve caching in get_calendar function

[WordPress Trac]

#61343: Improve caching in get_calendar function
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 Reporter:  spacedmonkey                         |       Owner:  (none)
     Type:  enhancement                          |      Status:  new
 Priority:  normal                               |   Milestone:  Awaiting
                                                 |  Review
Component:  Widgets                              |     Version:
 Severity:  normal                               |  Resolution:
 Keywords:  good-first-bug has-patch reporter-   |     Focuses:
  feedback has-unit-tests                        |  performance
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Comment (by MythThrazz):

 New PR in #11547 with a different approach than PR #6708:

 **Cache architecture:** Replaced the monolithic cache array (all
 variations in one key) with individual cache keys per variation
 (`get_calendar_{hash}`). Reads no longer deserialize all months/post-
 types, and writes only touch one entry.

 **Cache invalidation:** Switched from `save_post`/`delete_post` to
 `clean_post_cache` as suggested. Uses `wp_cache_flush_group('calendar')`
 with a generation counter fallback for persistent cache implementations
 that don't support group flushing.

 **Raw SQL kept:** The suggestion to replace `$wpdb` queries with
 `WP_Query` was evaluated but not implemented — `SELECT DISTINCT
 DAYOFMONTH(post_date)` returns max 31 rows, while `WP_Query` with
 `posts_per_page=-1` (as in PR #6708) would load all posts in the month.
 The raw queries are more efficient here.

 **Date math:** Replaced the MySQL `DATE_FORMAT(DATE_ADD(...))` query with
 PHP `gmdate()` to eliminate a DB roundtrip for pure date calculation.

 Includes unit tests for cache invalidation, individual keys, and
 flush_group behavior. All existing tests pass.

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Ticket URL: <https://core.trac.wordpress.org/ticket/61343#comment:9>
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