pg_upgrade: Use 50% CPU cores for vacuumdb (analyze) (#523)

vars/upgrade.yml

@@ -62,10 +62,11 @@ schema_compatibility_check: true  # If 'true', a compatibility check of the data
 schema_compatibility_check_port: "{{ (postgresql_port | int) + 1 }}"  # Port used to run a temporary PostgreSQL instance for schema compatibility checking.
 schema_compatibility_check_timeout: 3600  # Maximum duration (in seconds) for the compatibility check (using pg_dumpall --schema-only).
 
-vacuumdb_parallel_jobs: "{{ ansible_processor_vcpus }}"  # use all CPU cores
-vacuumdb_analyze_timeout: 3600  # seconds. The maximum duration of analyze command (soft limit, exceeding won't halt playbook)
 update_extensions: true  # if 'true', try to update extensions automatically
 
+vacuumdb_parallel_jobs: "{{ [ansible_processor_vcpus | int // 2, 1] | max }}"  # use 50% CPU cores
+vacuumdb_analyze_timeout: 3600  # seconds. The maximum duration of analyze command (soft limit, exceeding won't halt playbook)
+
 # Do not perform an upgrade if
 max_replication_lag_bytes: 10485760  # 10 MiB - Maximum allowed replication lag in bytes
 max_transaction_sec: 15  # Maximum allowed duration for a transactions in seconds