Speed up the Jekyll build times for large sites

[cotes2020]

Description

If the site has a large number of posts, and a lot of metadata (categories and tags from posts), then rendering the _includes/related-posts.html will be a bottleneck in build time.

Practical example:

With 1082 posts, 94 categories, and 26 tags, on a machine configured with Intel Core i7 CPU and 16GB RAM, the site's build time details are as follows:

Build Process Summary:

| PHASE    |     TIME |
+----------+----------+
| RESET    |   0.0003 |
| READ     |  34.1979 |
| GENERATE |   0.1318 |
| RENDER   | 123.6652 |
| CLEANUP  |   0.1728 |
| WRITE    |   0.7328 |


Site Render Stats:

| Filename                                                                                  | Count |     Bytes |    Time |
+-------------------------------------------------------------------------------------------+-------+-----------+---------+
| _layouts/page.html                                                                        |  1319 | 53683.56K | 107.046 |
| _includes/related-posts.html                                                              |  1085 | 31899.44K | 104.668 |
| _layouts/default.html                                                                     |  1319 | 87090.83K |   8.098 |
| _includes/head.html                                                                       |  1319 | 15723.82K |   4.609 |
| _layouts/home.html                                                                        |   109 |  2953.91K |   4.168 |
| _layouts/post.html                                                                        |  1085 |  7249.28K |   2.390 |
| _includes/js-selector.html                                                                |  1319 |  1149.73K |   1.207 |
| _includes/sidebar.html                                                                    |  1319 |  4068.55K |   1.203 |
| _includes/post-paginator.html                                                             |   109 |  1086.50K |   1.085 |
| _includes/datetime.html                                                                   |  7383 |  1248.77K |   0.881 |
| _includes/read-time.html                                                                  |  1085 |   293.66K |   0.836 |
| _includes/post-sharing.html                                                               |  1085 |  2381.29K |   0.747 |
| _includes/jsdelivr-combine.html                                                           |  1319 |   873.32K |   0.595 |
| _includes/post-nav.html                                                                   |  1085 |   663.21K |   0.560 |
| _includes/refactor-content.html                                                           |  1196 | 11139.09K |   0.491 |
| _includes/topbar.html                                                                     |  1319 |  1357.49K |   0.356 |
...
| _tabs/about.md                                                                            |     1 |     0.30K |   0.000 |
                    done in 158.944 seconds.

Type of change

• Improvement (refactoring and improving code)

Additional context

• Caching of expensive templates during rendering (trending-tags) #1094
• perf(build): use jekyll-include-cache plugin to reduce build time #1098

How has this been tested

For the same hardware with the same site files, executing the bundle exec jekyll b --profile command results in a significant reduction in build time.

Build Process Summary:

| PHASE    |    TIME |
+----------+---------+
| RESET    |  0.0002 |
| READ     | 32.4250 |
| GENERATE |  0.0847 |
| RENDER   | 32.1113 |
| CLEANUP  |  0.2832 |
| WRITE    |  0.8849 |


Site Render Stats:

| Filename                                                                                  | Count |     Bytes |   Time |
+-------------------------------------------------------------------------------------------+-------+-----------+--------+
| _layouts/page.html                                                                        |  1319 | 22114.94K | 17.042 |
| _includes/related-posts.html                                                              |  1085 |   330.82K | 14.423 |
| _layouts/default.html                                                                     |  1319 | 55522.21K |  6.963 |
| _layouts/home.html                                                                        |   109 |  2953.91K |  3.573 |
| _includes/head.html                                                                       |  1319 | 15723.82K |  3.251 |
| _layouts/post.html                                                                        |  1085 |  7249.28K |  2.677 |
| _includes/js-selector.html                                                                |  1319 |  1149.73K |  1.321 |
| _includes/sidebar.html                                                                    |  1319 |  4068.55K |  1.285 |
| _includes/post-paginator.html                                                             |   109 |  1086.50K |  1.097 |
| _includes/read-time.html                                                                  |  1085 |   293.66K |  0.922 |
| _includes/post-sharing.html                                                               |  1085 |  2381.29K |  0.917 |
| _includes/post-nav.html                                                                   |  1085 |   663.21K |  0.784 |
| _includes/jsdelivr-combine.html                                                           |  1319 |   873.32K |  0.663 |
| _includes/refactor-content.html                                                           |  1196 | 11139.09K |  0.530 |
| _includes/datetime.html                                                                   |  4128 |   733.82K |  0.497 |
| _includes/topbar.html                                                                     |  1319 |  1357.49K |  0.380 |
...
| _tabs/about.md                                                                            |     1 |     0.30K |  0.000 |

                    done in 65.825 seconds.