Improve performance of the `_wp_array_get` function

[aristath]

The _wp_array_get function gets called ~23k times on each page-load when using a block theme. In fact, it's the most-called function on the frontend of a site.

There is room for improvement here, and any tweaks we make can be beneficial.

Trac ticket: https://core.trac.wordpress.org/ticket/58376

Props @SergeyBiryukov @afercia @jrfnl

[spacedmonkey]

This is well worth doing, as this function is call 12k+ times on many page loads.

Moving into 6.3.

Brenchmarks.

Trunk
Response Time (median),109.43
wp-load-alloptions-query (median),0.61
wp-before-template (median),52.5
wp-before-template-db-queries (median),4.6
wp-template (median),50.45
wp-total (median),104.07
wp-template-db-queries (median),2.55

PR - e2f5b7562af632fcdefd0cfc92a7aa11e72158d6
Response Time (median),108.4
wp-load-alloptions-query (median),0.62
wp-before-template (median),51.75
wp-before-template-db-queries (median),4.54
wp-template (median),50.01
wp-total (median),102.57
wp-template-db-queries (median),2.51

[flixos90]

I also conducted two benchmarks, one for TT3 (block theme) and one for TT1 (classic theme). Results look positive indeed, it's a small enhancement, but it shows consistently, improving overall WordPress execution time by ~1%.

• Block theme wp-total improved from 158.34ms to 156.49ms (1.17%)
• Classic theme wp-total improved from 58.42ms to 57.55ms (1.49%)

Here are the full results: ​https://docs.google.com/spreadsheets/d/1nn12aoFpgqF6F8o20hLExhnanL_-dShAkLjaItKsxcI/edit

Shared another benchmark for block theme and classic theme in https://core.trac.wordpress.org/ticket/58376#comment:4 - this looks like a nice little enhancement indeed!

[samiamnot]

While speeding up _wp_array_get is nice, maybe we should be asking how to cut ~23k calls down to something manageable. Why is it called that many times per screen load?

[SergeyBiryukov]

Replying to samiamnot:

While speeding up _wp_array_get is nice, maybe we should be asking how to cut ~23k calls down to something manageable. Why is it called that many times per screen load?

That was one of my first thoughts here too, perhaps we could optimize that as well as part of the performance focus.

[SergeyBiryukov]

In 55851:

General: Improve performance of the _wp_array_get() function.

When using a block theme, _wp_array_get() is the most called function on the front end of a site.

This commit makes a few minor performance optimizations, which add up to a noticeable improvement.

Follow-up to [49135], [49143], [49580].

Props aristath, jrf, afercia, costdev, swissspidy, flixos90, spacedmonkey, mukesh27, samiamnot, SergeyBiryukov.
Fixes #58376.

Thanks for the PR! Merged in r55851.

[costdev]

Here are some results from a quick check loading the frontend while logged in as an admin (TT3 active, no plugins active).

Total calls to _wp_array_get(): 23873

Top 5:

• 9849 calls - WP_Theme_JSON::merge()
• 3559 calls - WP_Theme_JSON::get_property_value()
• 3283 calls - WP_Theme_JSON::get_default_slugs()
• 1340 calls - WP_Theme_JSON::get_metadata_boolean()
• 1129 calls - block_has_support()
• These top 5 account for 19160 calls, or ~80%.

[samiamnot]

Thank you @costdev . Fascinating. Can I assume that a legacy theme like TwentyFifteen or TwentySeventeen would have only a fraction of the calls to _wp_array_get()? @flixos90's numbers above seem to show classic themes being quicker overall, and I wonder how much is impacted by _wp_array_get() calls. Do we know what the second most frequently called function is for both classic and block themes?

Replying to costdev:

Here are some results from a quick check loading the frontend - TT3 active, no plugins active.

Total calls to _wp_array_get(): 23873

Top 5:

• 9849 calls - WP_Theme_JSON::merge()
• 3559 calls - WP_Theme_JSON::get_property_value()
• 3283 calls - WP_Theme_JSON::get_default_slugs()
• 1340 calls - WP_Theme_JSON::get_metadata_boolean()
• 1129 calls - block_has_support()
• These top 5 account for 19160 calls, or ~80%.

[costdev]

Same results for Twenty Fifteen and Twenty Seventeen

Total calls to _wp_array_get(): 4418

Top 5:

• 928 calls - WP_Theme_JSON::merge()
• 736 calls - ::wp_migrate_old_typography_shape()
• 703 calls - ::block_has_support()
• 588 calls - ::wp_register_typography_support()
• 390 calls - ::wp_register_colors_support()
• These top 5 account for 3345 calls, or ~75%.

[spacedmonkey]

@costdev Are you testing with WP_DEBUG enabled? If so, those numbers will be wrong. WP_DEBUG disabled some of the core caches and results in these numbers being higher than in production.

[samiamnot]

@costdev,
Thanks. It is interesting that there are 928 calls to WP_Theme_JSON::merge() when those themes do not even have a themes.json file as far as I know. Why ::wp_migrate_old_typography_shape() is called so may times seems strange to me.

[costdev]

@spacedmonkey Ah true! I disabled WP_DEBUG and output the results directly to the screen, this showed 9599 calls for Twenty-Twenty Three, and 3746 for Twenty Seventeen. What numbers are you getting?

[spacedmonkey]

@costdev The number depends on the blocks on the page. There is no exact number. There are many more calls in block themes.

[samiamnot]

Regardless of the actual number of calls the count of calls to _wp_array_get seems excessive. Is there a way to reduce it?

[aristath]

Replying to samiamnot:

Regardless of the actual number of calls the count of calls to _wp_array_get seems excessive. Is there a way to reduce it?

Yes, there are ways to reduce the number of calls to that function. I currently have a PR in Gutenberg to do just that - see ​https://github.com/WordPress/gutenberg/pull/51116 for more info.
It's still awaiting a review, but I'm hoping we can get this merged soon.

[spacedmonkey]

This function is called in a lot of places. In the most in.

block_has_support - 2091
wp_should_skip_block_supports_serialization - 731

Love to fix these places.

[flixos90]

@spacedmonkey @aristath I opened #58532 as a more specific follow up ticket. Would be great if you could take a look and share your thoughts or maybe start a PR.