LZ4 compression on RDS Postgres 14

Question

Does Postgres 14 on RDS support TOAST compression using LZ4?

https://www.postgresql.org/docs/14/runtime-config-client.html#GUC-DEFAULT-TOAST-COMPRESSION

Accepted Answer

Verified lz4 is available. 
* created RDS for PostgreSQL 14.1 instance
* SHOW default_toast_compression; returned pglz
* CREATE TABLE TESTLZ4(COL_1 text COMPRESSION lz4);
* INSERT INTO TESTLZ4 VALUES (repeat('123456789', 1000));
* SELECT pg_column_compression(COL_1) FROM TESTLZ4;  retured 'lz4'
* SET default_toast_compression TO lz4;
* SHOW default_toast_compression; returned lz4

Answer

Amazon Relational Database Service (Amazon RDS) for PostgreSQL does not have database wide compression. For variable length datatypes(text, varchar), RDS for PostgreSQL has TOAST (The oversized attribute storage technique) storage. TOAST by default uses pglz compression. Now with RDS for PostgreSQL 14 you can also use lz4 compression. The transparent compression handled by TOAST, and the option for compression in CREATE/ALTER TABLE are the extent of compression options in RDS for PostgreSQL.

Answer

Most of this type of information is also available via the [pg_config](https://www.postgresql.org/docs/current/view-pg-config.html) view.
-- on RDS Postgres 14.1 you can see --with-lz4 in the configure info.
```
postgres=> select name,setting from pg_config where name ilike 'configure';
   name    |                                                                                                                                                                                                                                                                               setting                                                                                          
-----------+-------------------------------------------------------------------------------------------------------------------------------------------
 CONFIGURE |  '--prefix=/rdsdbbin/postgres-14.1.R1' '--with-openssl' '--with-perl' '--with-tcl' '--with-ossp-uuid' '--with-libxml' '--with-pam' '--with-ldap' '--with-krb-srvnam=whatever' '--with-gssapi' '--with-libraries=/rdsdbbin/postgres-14.1.R1/lib' '--with-includes=/rdsdbbin/postgres-14.1.R1/include' '--enable-debug' '--with-llvm' 'LLVM_CONFIG=/build/llvm/bin/llvm-config' '--with-icu' 'ICU_CFLAGS=-I/rdsdbbin/postgres-14.1.R1/include -DU_STATIC_IMPLEMENTATION' '--with-lz4' 'ICU_LIBS=-L/rdsdbbin/postgres-14.1.R1/lib -licui18n -licuuc -licudata -lstdc++'
(1 row)
```

LZ4 compression on RDS Postgres 14

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