Default values of cluster parameters - PolarDB - Alibaba Cloud Documentation Center

This topic describes the default values of cluster parameters.

Parameters

The default values of PolarDB for Oracle parameters are a result of considering performance, availability, and reliability. They may be different from the default values of parameters for the community version. In particular, the default values of the parameters described in the following table are based on the principle of optimal performance. You can modify these parameters in the PolarDB console.

Parameter

Default value

Description

polar_comp_stmt_level_tx

off

Specifies whether to roll back uncommitted database updates in case of exceptions. Valid values:

on: Uncommitted database updates are not rolled back in case of exceptions. This rollback mechanism is the same as that in Oracle.
off: Uncommitted database updates are rolled back in case of exceptions.

Note

In Oracle, when a runtime error occurs in an SQL statement, all updates on the database caused by that single statement are rolled back. This is called statement-level transaction isolation. For example, if a single UPDATE statement updates five rows but an attempt to update a sixth row results in an exception, the updates to all six rows made by this UPDATE statement are rolled back. The effects of prior SQL statements that have not yet been committed or rolled back are pending until a COMMIT or ROLLBACK statement is executed. For more information about this parameter, see polar_comp_stmt_level_tx.
You can execute the following statement to view the settings of this parameter for the current cluster:
```
show polar_comp_stmt_level_tx;
```

log_statement

ddl

The level of audit logs. The default value is ddl, which indicates that only logs for DDL statements are audited. Displaying less logs can improve database performance.

Note

You can enable the audit log feature on the SQL Explorer page of the PolarDB console. Then, logs for all SQL statements are audited. For more information, see SQL Explorer.
You can execute the following statement to view the settings of this parameter for the current cluster:
```
show log_statement;
```

Default values of common cluster parameters

Parameter	Default value
authentication_timeout	60
autovacuum	on
autovacuum_analyze_scale_factor	0.05
autovacuum_analyze_threshold	50
autovacuum_freeze_max_age	1200000000
autovacuum_max_workers	5
autovacuum_multixact_freeze_max_age	1400000000
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 (PolarDB for Oracle 2.0) on (PolarDB for Oracle 1.0)
dynamic_shared_memory_type	posix
enable_partition_pruning	on
extra_float_digits	0
fsync	on
full_page_writes	off
gin_pending_list_limit	4096
hot_standby	on
hot_standby_feedback	on
huge_pages	on
idle_in_transaction_session_timeout	3600000
jit	off
lock_timeout	0
logging_collector	on
log_connections	off
log_disconnections	off
log_error_verbosity	default
log_min_duration_statement	5000
log_statement	ddl
max_files_per_process	1000
max_locks_per_transaction	64
max_prepared_transactions	800
max_replication_slots	64
max_worker_processes	256
polar_comp_stmt_level_tx	off
seq_page_cost	1
ssl	off
statement_timeout	0
synchronous_commit	on
temp_file_limit	524288000
timezone	'UTC'
wal_buffers	16 MB
wal_level	logical
wal_writer_delay	10