Add Get The Size Of An Index as a postgres til

README.md

@@ -7,7 +7,7 @@ variety of languages and technologies. These are things that don't really
 warrant a full blog post. These are mostly things I learn by pairing with
 smart people at [Hashrocket](http://hashrocket.com/).
 
-_408 TILs and counting..._
+_409 TILs and counting..._
 
 ---
 
@@ -200,6 +200,7 @@ _408 TILs and counting..._
 - [Generate Series Of Numbers](postgres/generate-series-of-numbers.md)
 - [Get The Size Of A Database](postgres/get-the-size-of-a-database.md)
 - [Get The Size Of A Table](postgres/get-the-size-of-a-table.md)
+- [Get The Size Of An Index](postgres/get-the-size-of-an-index.md)
 - [Getting A Slice Of An Array](postgres/getting-a-slice-of-an-array.md)
 - [Insert Just The Defaults](postgres/insert-just-the-defaults.md)
 - [Integers In Postgres](postgres/integers-in-postgres.md)

postgres/get-the-size-of-an-index.md

@@ -0,0 +1,23 @@
+# Get The Size Of An Index
+
+Want to get an idea of how much disk space that additional index is taking
+up? You can query for it with the same methods discussed in [Get The Size Of
+A Table](get-the-size-of-a-table.md) and [Pretty Print Data
+Sizes](pretty-print-data-sizes.md).
+
+For instance, if I have a table with a `users_pkey` index and a
+`users_unique_lower_email_idx` index, I can check the sizes like so:
+
+```sql
+> select pg_size_pretty(pg_relation_size('users_pkey'));
+ pg_size_pretty
+----------------
+ 240 kB
+
+> select pg_size_pretty(pg_relation_size('users_unique_lower_email_idx'));
+ pg_size_pretty
+----------------
+ 704 kB
+```
+
+[source](https://www.niwi.nz/2013/02/17/postgresql-database-table-indexes-size/)