[ci skip] Add info on how to use the buffers option in Postgres

The buffer option was added as part of the Active Record Explain as part of this PR: rails#47043

However perhaps they missed updating the guides on how to use this option as part of ActiveRecord Explain specifically in the context of the PostgreSQL DB

Author: boddhisattva

guides/source/active_record_postgresql.md

@@ -15,6 +15,8 @@ After reading this guide, you will know:
 * How to implement exclusion constraints.
 * How to implement full text search with PostgreSQL.
 * How to back your Active Record models with database views.
+* How to use Explain options to gain insights that could potentially further
+  improve PostgreSQL's query performance
 
 --------------------------------------------------------------------------------
 
@@ -807,3 +809,40 @@ For example, to exclude comments from your structure dump, add this to an initia
 ```ruby
 ActiveRecord::Tasks::DatabaseTasks.structure_dump_flags = ["--no-comments"]
 ```
+
+Explain options to give deeper insight into Query Performance
+--------------
+
+### Buffer
+
+The Buffer option that comes with PostgreSQL's `Explain` command gives one
+insights with regard to the data it is reading or writing when performing a
+query operation and which of that data comes from cache or another source like
+disk.
+
+The buffer option is intended to give you one or more hints into what
+specifically within the query your executing could be a potential cause of
+slowness and thereby has room for further improvement.
+
+
+An example Active Record query that uses `explain` with the `buffers` option:
+
+```ruby
+Company.where(id: owning_companies_ids).explain(:analyze, :buffers)
+```
+
+Output of above query:
+
+```sql
+=> EXPLAIN (ANALYZE, BUFFERS) SELECT "companies".* FROM "companies"
+WHERE "companies"."id" IN ($1, $2, $3) [["id", 365], ["id", 364], ["id", 360]]
+QUERY PLAN
+-------------------------------------------------------------------------------
+ Seq Scan on companies  (cost=0.00..2.21 rows=3 width=64)
+ (actual time=0.009..0.012 rows=3 loops=1)
+   Filter: (id = ANY ('{365,364,360}'::bigint[]))
+   Rows Removed by Filter: 10
+   Buffers: shared hit=1
+ Planning Time: 0.023 ms
+ Execution Time: 0.011 ms
+ ```

wrap_text.md

@@ -0,0 +1,35 @@
+How to use Explain options to gain insights that could potentially further
+improve PostgreSQL's query performance
+
+Explain options to give deeper insight into Query Performance
+--------------
+
+
+### Buffer
+
+The Buffer option that comes with PostgreSQL's `Explain` command gives one
+insights with regard to the data it is reading or writing when performing a
+query operation and which of that data comes from cache or another source like
+disk.
+
+The buffer option is intended to give you one or more hints into what
+specifically within the query your executing could be a potential cause of
+slowness and thereby has room for further improvement.
+
+
+An example Active Record query that uses `explain` with the `buffers` option:
+
+```ruby Company.where(id: owning_companies_ids).explain(:analyze, :buffers) ```
+
+Output of above query:
+
+```sql
+=> EXPLAIN (ANALYZE, BUFFERS) SELECT "companies".* FROM "companies"
+WHERE "companies"."id" IN ($1, $2, $3) [["id", 365], ["id", 364], ["id", 360]]
+QUERY PLAN
+-------------------------------------------------------------------------------
+ Seq Scan on companies  (cost=0.00..2.21 rows=3 width=64)
+ (actual time=0.009..0.012 rows=3 loops=1) Filter: (id = ANY ('
+ {365,364,360}'::bigint[])) Rows Removed by Filter: 10 Buffers: shared hit=1
+ Planning Time: 0.049 ms Execution Time: 0.023 ms(6 rows)
+ ```