Taking care of review comments

Adjusting provider_name length in pg_tde_key_provider catalog
definition and adding a TODO note for implementing an eviction
policy for the master key cache.

pg_tde--1.0.sql

@@ -10,7 +10,7 @@ CREATE SCHEMA percona_tde;
 -- and we do not want to encrypt this table using pg_tde.
 CREATE TABLE percona_tde.pg_tde_key_provider(provider_id SERIAL,
         keyring_type VARCHAR(10) CHECK (keyring_type IN ('file', 'vault-v2')),
-        provider_name VARCHAR(256) UNIQUE NOT NULL, options JSON, PRIMARY KEY(provider_id)) using heap;
+        provider_name VARCHAR(255) UNIQUE NOT NULL, options JSON, PRIMARY KEY(provider_id)) using heap;
 
 -- If you want to add new provider types, you need to make appropriate changes
 -- in include/catalog/tde_keyring.h and src/catalog/tde_keyring.c files.

src/catalog/tde_master_key.c

@@ -475,7 +475,14 @@ get_master_key_from_cache(bool acquire_lock)
 }
 
 /*
- * push the master key for current database to the shared memory cache
+ * Push the master key for current database to the shared memory cache.
+ * TODO: Add eviction policy
+ * For now we just keep pushing the master keys to the cache and do not have
+ * any eviction policy. We have one master key for a database, so at max,
+ * we could have as many entries in the cache as the number of databases.
+ * Which in practice would not be a huge number, but still we need to have
+ * some eviction policy in place. Moreover, we need to have some mechanism to
+ * remove the cache entry when the database is dropped.
  */
 static void
 push_master_key_to_cache(TDEMasterKey *masterKey)