Default values of cluster parameters

PolarDB for PostgreSQL (Compatible with Oracle) pre-tunes a set of parameters from the community PostgreSQL defaults to deliver high performance and stability in a cloud environment. Use this reference to understand what PolarDB has changed and how to adjust parameters for your workload.

To check the current value of any parameter, run:

SHOW <parameter_name>;

Modify parameters in the PolarDB console. For parameters marked Requires restart, the database restarts automatically after you save the change—plan accordingly.

Key parameters

PolarDB sets the following parameters to non-community defaults. PolarDB-specific parameters (prefixed with polar_) are extensions to the standard PostgreSQL engine.

`polar_comp_stmt_level_tx`

Controls whether a runtime exception rolls back only the failed statement or the entire transaction.

Compatibility version	Default	Behavior
Oracle syntax compatibility 2.0	ON	Exceptions do not automatically roll back previous uncommitted updates. Only the failed statement is rolled back, matching Oracle's statement-level transaction isolation behavior.
Oracle syntax compatibility 1.0	OFF	Exceptions roll back all uncommitted updates in the transaction.

In Oracle syntax compatibility 2.0, this parameter is renamed to polar_enable_stmt_transaction_rollback. For a detailed explanation of statement-level transaction isolation, see polar_comp_stmt_level_tx.

`wal_level`

Controls how much information is written to the write-ahead log (WAL).

Value	Default	Description
`replica`	Yes	WAL contains enough information for streaming replication but not logical decoding. Reduces WAL volume and improves write throughput.
`logical`	No	WAL contains additional information required for logical replication. Increases WAL volume.

Warning

Changing wal_level requires a database restart. Schedule this change during a maintenance window.

`log_statement`

Sets which SQL statements are written to the audit log. Logging fewer statements reduces I/O overhead and improves performance.

Value	Default	Statements logged
`none`	No	None
`ddl`	Yes	DDL statements (`CREATE`, `ALTER`, `DROP`)
`mod`	No	DDL and DML statements (`INSERT`, `UPDATE`, `DELETE`)
`all`	No	All SQL statements

Enabling the SQL Explorer and Audit feature in the console sets log_statement = all. Disabling it resets log_statement = ddl.

Default values of common cluster parameters

All parameters below are standard PostgreSQL engine parameters.

Parameter	Unit	Default value
`authentication_timeout`	seconds	60
`autovacuum`	—	on
`autovacuum_analyze_scale_factor`		0.05
`autovacuum_analyze_threshold`		50
`autovacuum_freeze_max_age`		500000000
`autovacuum_max_workers`		5
`autovacuum_multixact_freeze_max_age`		700000000
`autovacuum_naptime`		30
`autovacuum_vacuum_cost_delay`		0
`autovacuum_vacuum_cost_limit`		10000
`autovacuum_vacuum_scale_factor`		0.02
`autovacuum_vacuum_threshold`		50
`backend_flush_after`		0
`bgwriter_delay`		10
`checkpoint_timeout`		30
`constraint_exclusion`	—	partition
`cpu_index_tuple_cost`		0.005
`cpu_operator_cost`		0.0025
`cpu_tuple_cost`		0.01
`datestyle`	—	'ISO,YMD'
`deadlock_timeout`		1000
`default_with_oids`	—	off
`dynamic_shared_memory_type`	—	posix
`enable_partition_pruning`	—	on
`enormous_pages`	—	on
`extra_float_digits`		0
`fsync`	—	on
`full_page_writes`	—	off
`gin_pending_list_limit`		4096
`hot_standby`	—	on
`hot_standby_feedback`	—	on
`idle_in_transaction_session_timeout`		3600000
`jit`	—	off
`lock_timeout`		0
`log_connections`	—	off
`log_disconnections`	—	off
`log_error_verbosity`	—	default
`log_min_duration_statement`		5000
`log_statement`	—	ddl
`logging_collector`	—	on
`max_files_per_process`		10000
`max_locks_per_transaction`		64
`max_prepared_transactions`		800
`max_replication_slots`		64
`max_worker_processes`		256
`seq_page_cost`		1
`ssl`	—	off
`statement_timeout`		0
`synchronous_commit`	—	off
`temp_file_limit`	GB	100
`timezone`	—	'UTC'
`wal_buffers`	MB	16
`wal_level`	—	replica
`wal_writer_delay`		10