The REINDEX command acquires AccessExclusiveLock table lock . Following are the locks REINDEX acquires, the commands that are allowed to run concurrently with its lock AccessExclusiveLock and the commands that conflict with it. The list also includes the conflicting row locks if applicable
Commands concurrently allowed on the table with REINDEX
Nothing is allowed to run concurrently with REINDEX
Commands conflicting with REINDEX on the table
e.g. If tx1 does a REINDEX on the table then concurrently tx2 tries to do any of the following commands on the same table, tx2 will be blocked. Conversely, if tx1 executes any of the following commands and then tx2 concurrently tries to execute REINDEX, tx2 will block.