Block Template persistent cache- transient + object cache.

[kt-12]

Trac ticket: https://core.trac.wordpress.org/ticket/59600

Tested Performance for Memcache version on Trunk and PR - Trunk median was 114.6 and PR median was 113

I also tested the transient version on Trunk and PR but could see a downgrade of around 5 ms.

However, I am not confident about the result as I could see drastic performance fluctuation and had to do the test several rounds to get a convincing stable result.

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[kt-12]

Thanks @kt-12. When running some profiling data on this approach, I'm not seeing much benefit to adding a cache at this point in the execution process.

Comparing runs of _build_block_template_result_from_file() with and without this cache in place, there is a marginal improvement and seems like the need to query the DB for these transients offsets any benefit in avoiding the file_get_contents() calls. In fact, this function is only responsible for ~1% of the overall execution time of the TT4 homepage without additional caching, so I'm not sure there is a benefit in adding caching here.

_build_block_template_result_from_file()

Trunk

Current PR

get_block_templates()

However, its parent function, get_block_templates(), does seem to be present a bigger opportunity for improvement, as it's profiling at 5% of iwt for the same requests. Of that time, most of the cost seems to from _get_block_templates_files(), with most of that processing eventually happening in wp_get_theme_data_custom_templates() when the WP_Theme_JSON_Resolver::get_theme_data() parses the customTemplates property from the WP_Theme_JSON data provided by the theme.

I think we could consider adding a cache to either `_get_block_templates_files()` or `wp_get_theme_data_custom_templates()` to have bigger impact—at least until we are able to handle some/all of https://core.trac.wordpress.org/ticket/57789.

I was investigating the performance opportunity get_block_templates() - Down the line, this function is calling WP_Theme_JSON_Resolver::get_theme_data which is the major reason for the performance. At the moment, get_theme_data is static cached so, even if we persistent cache get_block_templates we won't get any benefit as get_theme_data is referred at two more places and the next function calling it will take the hit.