Re: pg_basebackup failure after setting default_table_access_method option

Hi,

I noticed pg_basebackup failure when default_table_access_method option is set.

Test steps:

Step 1: Init database 

./initdb -D data

Step 2: Start Server

./postgres -D data &

Step 3: Set Guc option 

export PGOPTIONS='-c default_table_access_method=zheap'

Step 4: Peform backup

/pg_basebackup -D backup -p 5432 --no-sync

2019-06-05 20:35:04.088 IST [11601] FATAL:  cannot read pg_class without having selected a database

pg_basebackup: error: could not connect to server: FATAL:  cannot read pg_class without having selected a database

Reason why it is failing:

pg_basebackup does not use any database to connect to server as it backs up the whole data instance. 

As the option default_table_access_method is set.

It tries to validate this option, but while validating the option in ScanPgRelation function:

if (!OidIsValid(MyDatabaseId))

elog(FATAL, "cannot read pg_class without having selected a database");

Here as pg_basebackup uses no database the command fails.

Fix:

The patch has the fix for the above issue:

Let me know your opinion on this.