Configuration Parameters

In total, we provide users three kinds of configurations module:

environment configuration file (, iotdb-env.sh). The default configuration file for the environment configuration item. Users can configure the relevant system configuration items of JAVA-JVM in the file.
system configuration file (iotdb-engine.properties).
- iotdb-engine.properties: The default configuration file for the IoTDB engine layer configuration item. Users can configure the IoTDB engine related parameters in the file, such as JDBC service listening port (rpc_port), unsequence data storage directory (unsequence_data_dir), etc. What’s more, Users can configure the information about the TsFile, such as the data size written to the disk per time().
log configuration file (logback.xml)

The configuration files of the three configuration items are located in the IoTDB installation directory: $IOTDB_HOME/conf folder.

Trigger way: The client sends the command to the IoTDB server. See Chapter 4 for the usage of the client.

The environment configuration file is mainly used to configure the Java environment related parameters when IoTDB Server is running, such as JVM related configuration. This part of the configuration is passed to the JVM when the IoTDB Server starts. Users can view the contents of the environment configuration file by viewing the iotdb-env.sh (or iotdb-env.bat) file.

The detail of each variables are as follows:

MAX_HEAP_SIZE

HEAP_NEWSIZE

Name	HEAP_NEWSIZE
Description	The minimum heap memory size that IoTDB can use at startup.
Type	String
Default	On Linux or MacOS, the default is min{cores * 100M, one quarter of MAX_HEAP_SIZE}. On Windows, the default value for 32-bit systems is 512M, and the default for 64-bit systems is 2G.
Effective	After restarting system

JMX_LOCAL

Name	JMX_LOCAL
Description	JMX monitoring mode, configured as yes to allow only local monitoring, no to allow remote monitoring
Type	Enum String: “true”, “false”
Default	true
Effective	After restarting system

JMX_PORT

Name	JMX_PORT
Description	JMX listening port. Please confirm that the port is not a system reserved port and is not occupied
Type	Short Int: [0,65535]
Default	31999
Effective	After restarting system

JMX_IP

Name	JMX_IP
Description	JMX listening address. Only take effect if JMX_LOCAL=false. 0.0.0.0 is never allowed
Type	String
Default	127.0.0.1
Effective	After restarting system

We STRONGLY RECOMMENDED you CHANGE the PASSWORD for the JMX remote connection.

The permission definitions are in ${IOTDB_CONF}/conf/jmx.access.

compressor

Name	compressor
Description	Data compression method
Type	Enum String : “UNCOMPRESSED”, “SNAPPY”
Default	UNCOMPRESSED
Effective	Trigger

group_size_in_byte

Name	group_size_in_byte
Description	The data size written to the disk per time
Type	Int32
Default	134217728
Effective	Trigger

page_size_in_byte

Name	page_size_in_byte
Description	The maximum size of a single page written in memory when each column in memory is written (in bytes)
Type	Int32
Default	65536
Effective	Trigger

max_number_of_points_in_page

Name	max_number_of_points_in_page
Description	The maximum number of data points (timestamps - valued groups) contained in a page
Type	Int32
Default	1048576
Effective	Trigger

max_degree_of_index_node

Name	max_degree_of_index_node
Description	The maximum degree of the metadata index tree (that is, the max number of each node’s children)
Type	Int32
Default	256
Effective	Only allowed to be modified in first start up

max_string_length

Name	max_string_length
Description	The maximum length of a single string (number of character)
Type	Int32
Default	128
Effective	Trigger

time_encoder

Name	time_encoder
Description	Encoding type of time column
Type	Enum String: “TS_2DIFF”,“PLAIN”,“RLE”
Default	TS_2DIFF
Effective	Trigger

value_encoder

Name	value_encoder
Description	Encoding type of value column
Type	Enum String: “TS_2DIFF”,“PLAIN”,“RLE”
Default	PLAIN
Effective	Trigger

float_precision

Name	float_precision
Description	The precision of the floating point number.(The number of digits after the decimal point)
Type	Int32
Default	The default is 2 digits. Note: The 32-bit floating point number has a decimal precision of 7 bits, and the 64-bit floating point number has a decimal precision of 15 bits. If the setting is out of the range, it will have no practical significance.
Effective	Trigger

bloomFilterErrorRate

Name	bloomFilterErrorRate
Description	The false positive rate of bloom filter in each TsFile. Bloom filter checks whether a given time series is in the tsfile before loading metadata. This can improve the performance of loading metadata and skip the tsfile that doesn’t contain specified time series. If you want to learn more about its mechanism, you can refer to: wiki page of bloom filter (opens new window).
Type	float, (0, 1)
Default	0.05
Effective	After restarting system

Engine Layer

rpc_address

Name	rpc_address
Description	The jdbc service listens on the address.
Type	String
Default	“0.0.0.0”
Effective	After restarting system

rpc_port

Name	rpc_port
Description	The jdbc service listens on the port. Please confirm that the port is not a system reserved port and is not occupied.
Type	Short Int : [0,65535]
Default	6667
Effective	After restarting system

rpc_thrift_compression_enable

Name	rpc_thrift_compression_enable
Description	Whether enable thrift’s compression (using GZIP).
Type	Boolean
Default	false
Effective	After restarting system

rpc_advanced_compression_enable

Name	rpc_advanced_compression_enable
Description	Whether enable thrift’s advanced compression.
Type	Boolean
Default	false
Effective	After restarting system

time_zone

Name	time_zone
Description	The time zone in which the server is located, the default is Beijing time (+8)
Type	Time Zone String
Default	+08:00
Effective	Trigger

base_dir

Name	base_dir
Description	The IoTDB system folder. It is recommended to use an absolute path.
Type	String
Default	data
Effective	After restarting system

data_dirs

Name	data_dirs
Description	The directories of data files. Multiple directories are separated by comma. The starting directory of the relative path is related to the operating system. It is recommended to use an absolute path. If the path does not exist, the system will automatically create it.
Type	String[]
Default	data/data
Effective	Trigger

wal_dir

Name	wal_dir
Description	Write Ahead Log storage path. It is recommended to use an absolute path.
Type	String
Default	data/wal
Effective	After restarting system

enable_wal

Name	enable_wal
Description	Whether to enable the pre-write log. The default value is true(enabled), and false means closed.
Type	Bool
Default	true
Effective	Trigger

Name	enable_mem_control
Description	enable memory control to avoid OOM
Type	Bool
Default	true
Effective	After restarting system

memtable_size_threshold

Name	memtable_size_threshold
Description	max memtable size
Type	Long
Default	1073741824
Effective	when enable_mem_control is false & After restarting system

enable_timed_flush_seq_memtable

Name	enable_timed_flush_seq_memtable
Description	whether to enable timed flush sequence memtable
Type	Bool
Default	false
Effective	Trigger

seq_memtable_flush_interval_in_ms

Name	seq_memtable_flush_interval_in_ms
Description	if a memTable’s created time is older than current time minus this, the memtable will be flushed to disk
Type	Int32
Default	3600000
Effective	Trigger

seq_memtable_flush_check_interval_in_ms

Name	seq_memtable_flush_check_interval_in_ms
Description	the interval to check whether sequence memtables need flushing
Type	Int32
Default	600000
Effective	Trigger

enable_timed_flush_unseq_memtable

Name	enable_timed_flush_unseq_memtable
Description	whether to enable timed flush unsequence memtable
Type	Bool
Default	false
Effective	Trigger

unseq_memtable_flush_interval_in_ms

Name	unseq_memtable_flush_interval_in_ms
Description	if a memTable’s created time is older than current time minus this, the memtable will be flushed to disk
Type	Int32
Default	3600000
Effective	Trigger

unseq_memtable_flush_check_interval_in_ms

Name	unseq_memtable_flush_check_interval_in_ms
Description	the interval to check whether unsequence memtables need flushing
Type	Int32
Default	600000
Effective	Trigger

enable_timed_close_tsfile

Name	enable_timed_close_tsfile
Description	whether to timed close tsfiles
Type	Bool
Default	false
Effective	Trigger

close_tsfile_interval_after_flushing_in_ms

Name	close_tsfile_interval_after_flushing_in_ms
Description	if a TsfileProcessor’s last working memtable flush time is older than current time minus this and its working memtable is null, the TsfileProcessor will be closed
Type	Int32
Default	3600000
Effective	Trigger

close_tsfile_check_interval_in_ms

Name	close_tsfile_check_interval_in_ms
Description	the interval to check whether tsfiles need closing
Type	Int32
Default	600000
Effective	Trigger

avg_series_point_number_threshold

Name	avg_series_point_number_threshold
Description	max average number of point of each series in memtable
Type	Int32
Default	10000
Effective	After restarting system

tsfile_size_threshold

Name	tsfile_size_threshold
Description	max tsfile size
Type	Long
Default	536870912
Effective	After restarting system

enable_partition

partition_interval

Name	partition_interval
Description	Time range for dividing storage group, time series data will be divided into groups by this time range
Type	Int64
Default	604800
Effective	Only allowed to be modified in first start up

concurrent_writing_time_partition

Name	concurrent_writing_time_partition
Description	This config decides how many time partitions in a storage group can be inserted concurrently For example, your partitionInterval is 86400 and you want to insert data in 5 different days,
Type	Int32
Default	1
Effective	After restarting system

multi_dir_strategy

Name	multi_dir_strategy
Description	IoTDB’s strategy for selecting directories for TsFile in tsfile_dir. You can use a simple class name or a full name of the class. The system provides the following three strategies: 1. SequenceStrategy: IoTDB selects the directory from tsfile_dir in order, traverses all the directories in tsfile_dir in turn, and keeps counting; 2. MaxDiskUsableSpaceFirstStrategy: IoTDB first selects the directory with the largest free disk space in tsfile_dir; 3. MinFolderOccupiedSpaceFirstStrategy: IoTDB prefers the directory with the least space used in tsfile_dir; 4. UserDfineStrategyPackage (user-defined policy) You can complete a user-defined policy in the following ways: 1. Inherit the cn.edu.tsinghua.iotdb.conf.directories.strategy.DirectoryStrategy class and implement its own Strategy method; 2. Fill in the configuration class with the full class name of the implemented class (package name plus class name, UserDfineStrategyPackage); 3. Add the jar file to the project.
Type	String
Default	MaxDiskUsableSpaceFirstStrategy
Effective	Trigger

tsfile_size_threshold

Name	tsfile_size_threshold
Description	When a TsFile size on the disk exceeds this threshold, the TsFile is closed and open a new TsFile to accept data writes. The unit is byte and the default value is 2G.
Type	Int64
Default	536870912
Effective	After restarting system

tag_attribute_total_size

Name	tag_attribute_total_size
Description	The maximum persistence size of tags and attributes of each time series.
Type	Int32
Default	700
Effective	Only allowed to be modified in first start up

tag_attribute_flush_interval

Name	tag_attribute_flush_interval
Description	interval num for tag and attribute records when force flushing to disk. When a certain amount of tag and attribute records is reached, they will be force flushed to disk. It is possible to lose at most tag_attribute_flush_interval records
Type	Int32
Default	1000
Effective	Only allowed to be modified in first start up

enable_partial_insert

Name	enable_partial_insert
Description	Whether continue to write other measurements if some measurements are failed in one insertion.
Type	Bool
Default	true
Effective	After restarting system

mtree_snapshot_interval

Name	mtree_snapshot_interval
Description	The least interval line numbers of mlog.txt when creating a checkpoint and saving snapshot of MTree. Unit: line numbers
Type	Int32
Default	100000
Effective	After restarting system

mlog_buffer_size

Name	mlog_buffer_size
Description	size of log buffer in each metadata operation plan(in byte)
Type	Int32
Default	1048576
Effective	After restart system

sync_mlog_period_in_ms

Name	sync_mlog_period_in_ms
Description	The cycle when metadata log is periodically forced to be written to disk(in milliseconds). If force_mlog_period_in_ms = 0 it means force metadata log to be written to disk after each refreshment
Type	Int64
Default	100
Effective	After restart system

flush_wal_threshold

Name	flush_wal_threshold
Description	After the WAL reaches this value, it is flushed to disk, and it is possible to lose at most flush_wal_threshold operations.
Type	Int32
Default	10000
Effective	Trigger

force_wal_period_in_ms

Name	force_wal_period_in_ms
Description	The period during which the log is periodically forced to flush to disk(in milliseconds)
Type	Int32
Default	10
Effective	Trigger

fetch_size

Name	fetch_size
Description	The amount of data read each time in batch (the number of data strips, that is, the number of different timestamps.)
Type	Int32
Default	10000
Effective	After restarting system

enable_stat_monitor

Name	enable_stat_monitor
Description	Whether to enable background statistics
Type	Boolean
Default	false
Effective	After restarting system

concurrent_flush_thread

Name	concurrent_flush_thread
Description	The thread number used to perform the operation when IoTDB writes data in memory to disk. If the value is less than or equal to 0, then the number of CPU cores installed on the machine is used. The default is 0.
Type	Int32
Default	0
Effective	After restarting system

concurrent_query_thread

Name	concurrent_query_thread
Description	The thread number which can concurrently execute query statement. When <= 0, use CPU core number. The default is 16.
Type	Int32
Default	16
Effective	After restarting system

concurrent_sub_rawQuery_thread

Name	concurrent_sub_rawQuery_thread
Description	The thread number which can concurrently read data for raw data query. When <= 0, use CPU core number. The default is 8.
Type	Int32
Default	8
Effective	After restarting system

tsfile_storage_fs

Name	tsfile_storage_fs
Description	The storage file system of Tsfile and related data files. Currently LOCAL file system and HDFS are supported.
Type	String
Default	LOCAL
Effective	Only allowed to be modified in first start up

core_site_path

Name	core_site_path
Description	Absolute file path of core-site.xml if Tsfile and related data files are stored in HDFS.
Type	String
Default	/etc/hadoop/conf/core-site.xml
Effective	After restarting system

hdfs_site_path

Name	hdfs_site_path
Description	Absolute file path of hdfs-site.xml if Tsfile and related data files are stored in HDFS.
Type	String
Default	/etc/hadoop/conf/hdfs-site.xml
Effective	After restarting system

hdfs_ip

Name	hdfs_ip
Description	IP of HDFS if Tsfile and related data files are stored in HDFS. If there are more than one hdfs_ip in configuration, Hadoop HA is used.
Type	String
Default	localhost
Effective	After restarting system

hdfs_port

Name	hdfs_port
Description	Port of HDFS if Tsfile and related data files are stored in HDFS
Type	String
Default	9000
Effective	After restarting system

dfs_nameservices

Name	hdfs_nameservices
Description	Nameservices of HDFS HA if using Hadoop HA
Type	String
Default	hdfsnamespace
Effective	After restarting system

dfs_ha_namenodes

Name	hdfs_ha_namenodes
Description	Namenodes under DFS nameservices of HDFS HA if using Hadoop HA
Type	String
Default	nn1,nn2
Effective	After restarting system

dfs_ha_automatic_failover_enabled

Name	dfs_ha_automatic_failover_enabled
Description	Whether using automatic failover if using Hadoop HA
Type	Boolean
Default	true
Effective	After restarting system

dfs_client_failover_proxy_provider

Name	dfs_client_failover_proxy_provider
Description	Proxy provider if using Hadoop HA and enabling automatic failover
Type	String
Default	org.apache.hadoop.hdfs.server.namenode.ha.ConfiguredFailoverProxyProvider
Effective	After restarting system

hdfs_use_kerberos

Name	hdfs_use_kerberos
Description	Whether use kerberos to authenticate hdfs
Type	String
Default	false
Effective	After restarting system

kerberos_keytab_file_path

Name	kerberos_keytab_file_path
Description	Full path of kerberos keytab file
Type	String
Default	/path
Effective	After restarting system

kerberos_principal

Name	kerberos_principal
Description	Kerberos pricipal
Type	String
Default	your principal
Effective	After restarting system

authorizer_provider_class

Name	authorizer_provider_class
Description	the class name of the authorization service
Type	String
Default	org.apache.iotdb.db.auth.authorizer.LocalFileAuthorizer
Effective	After restarting system
Other available values	org.apache.iotdb.db.auth.authorizer.OpenIdAuthorizer

openID_url

Name	openID_url
Description	the openID server if OpenIdAuthorizer is enabled
Type	String (a http url)
Default	no
Effective	After restarting system

Name	thrift_max_frame_size
Description	the max bytes in a RPC request/response
Type	long
Default	536870912 (should >= 512 1024 1024)
Effective	After restarting system

InfluxDB-Protocol Adaptor

enable_influxdb_rpc_service

Name	enable_influxdb_rpc_service
Description	Whether to enable InfluxDB RPC service
Type	Boolean
Default	true
Effective	After restarting system

influxdb_rpc_port

Name	influxdb_rpc_port
Description	The port used by InfluxDB RPC service
Type	INT32
Default	8086
Effective	After restarting system

default_fill_interval

Name	default_fill_interval
Description	Default interval of `group by fill` query in ms
Type	Int32
Default	-1
Effective	After restarting system

group_by_fill_cache_size_in_mb

Name	group_by_fill_cache_size_in_mb
Description	Cache size of `group by fill` query
Type	Float
Default	1.0
Effective	After restarting system

Compaction Config

enable_seq_space_compaction

enable_unseq_space_compaction

Name	enable_unseq_space_compaction
Description	enable the compaction between unsequence files
Type	Boolean
Default	false
Effective	After restart system

enable_cross_space_compaction

Name	enable_cross_space_compaction
Description	enable the compaction between sequence files and unsequence files
Type	Boolean
Default	true
Effective	After restart system

cross_compaction_strategy

Name	cross_compaction_strategy
Description	strategy of cross space compaction
Type	String
Default	rewrite_compaction
Effective	After restart system

inner_compaction_strategy

Name	inner_compaction_strategy
Description	strategy of inner space compaction
Type	String
Default	size_tiered_compaction
Effective	After restart system

compaction_priority

Name	compaction_priority
Description	Priority of compaction task. When it is BALANCE, system executes all types of compaction equally; when it is INNER_CROSS, system takes precedence over executing inner space compaction task; when it is CROSS_INNER, system takes precedence over executing cross space compaction task
Type	String
Default	BALANCE
Effective	After restart system

target_compaction_file_size

Name	target_compaction_file_size
Description	The target file is in inner space compaction
Type	Int64
Default	1073741824
Effective	After restart system

target_chunk_size

Name	target_chunk_size
Description	The target size of compacted chunk
Type	Int64
Default	1048576
Effective	After restart system

target_chunk_point_num

Name	target_chunk_point_num
Description	The target point number of compacted chunk
Type	Int32
Default	100000
Effective	After restart system

chunk_size_lower_bound_in_compaction

Name	chunk_size_lower_bound_in_compaction
Description	A source chunk will be deserialized in compaction when its size is less than this value
Type	Int64
Default	128
Effective	After restart system

chunk_point_num_lower_bound_in_compaction

Name	chunk_size_lower_bound_in_compaction
Description	A source chunk will be deserialized in compaction when its point num is less than this value
Type	Int32
Default	100
Effective	After restart system

max_inner_compaction_candidate_file_num

Name	max_inner_compaction_candidate_file_num
Description	The max num of files encounter in inner space compaction
Type	Int32
Default	30
Effective	After restart system

max_cross_compaction_file_num

Name	max_cross_compaction_candidate_file_num
Description	The max num of files encounter in cross space compaction
Type	Int32
Default	1000
Effective	After restart system

cross_compaction_file_selection_time_budget

Name	cross_compaction_file_selection_time_budget
Description	Time budget for cross space compaction file selection
Type	Int32
Default	30000
Effective	After restart system

cross_compaction_memory_budget

Name	cross_compaction_memory_budget
Description	Memory budget for a cross space compaction
Type	Int32
Default	2147483648
Effective	After restart system

concurrent_compaction_thread

Name	concurrent_compaction_thread
Description	thread num to execute compaction
Type	Int32
Default	10
Effective	After restart system

compaction_schedule_interval_in_ms

Name	compaction_schedule_interval_in_ms
Description	interval of scheduling compaction
Type	Int64
Default	60000
Effective	After restart system

compaction_submission_interval_in_ms

Name	compaction_submission_interval_in_ms
Description	interval of submitting compaction task
Type	Int64
Default	60000
Effective	After restart system

compaction_write_throughput_mb_per_sec

Name	compaction_write_throughput_mb_per_sec
Description	The write rate of all compaction tasks in MB/s
Type	Int32
Default	16
Effective	After restart system

Insertion

insert_multi_tablet_enable_multithreading_column_threshold

Name	insert_multi_tablet_enable_multithreading_column_threshold
Description	When the insert plan column count reaches the specified threshold, multi-threading is enabled.
Type	Int32
Default	10
Effective	After restarting system

enable_auto_create_schema

Name	enable_auto_create_schema
Description	whether auto create the time series when a non-existed time series data comes
Type	true or false
Default	true
Effective	After restarting system

default_storage_group_level

Name	default_storage_group_level
Description	Storage group level when creating schema automatically is enabled. For example, if we receives a data point from root.sg0.d1.s2, we will set root.sg0 as the storage group if storage group level is 1. (root is level 0)
Type	integer
Default	1
Effective	After restarting system

boolean_string_infer_type

Name	boolean_string_infer_type
Description	To which type the values “true” and “false” should be reslved
Type	BOOLEAN or TEXT
Default	BOOLEAN
Effective	After restarting system

integer_string_infer_type

Name	integer_string_infer_type
Description	To which type an integer string like “67” in a query should be resolved
Type	INT32, INT64, DOUBLE, FLOAT or TEXT
Default	DOUBLE
Effective	After restarting system

nan_string_infer_type

Name	nan_string_infer_type
Description	To which type the value NaN in a query should be resolved
Type	DOUBLE, FLOAT or TEXT
Default	FLOAT
Effective	After restarting system

floating_string_infer_type

Name	floating_string_infer_type
Description	To which type a floating number string like “6.7” in a query should be resolved
Type	DOUBLE, FLOAT or TEXT
Default	FLOAT
Effective	After restarting system

enable_partition

Name	enable_partition
Description	whether enable data partition. If disabled, all data belongs to partition 0
Type	BOOLEAN
Default	false
Effective	Only allowed to be modified in first start up

partition_interval

Name	partition_interval
Description	time range for partitioning data inside each storage group, the unit is second
Type	LONG
Default	604800
Effective	Only allowed to be modified in first start up

virtual_storage_group_num

Name	virtual_storage_group_num
Description	number of virtual storage groups per user-defined storage group, a virtual storage group is the unit of parallelism in memory as all ingestions in one virtual storage group are serialized, recommended value is [virtual storage group number] = [CPU core number] / [user-defined storage group number]
Type	LONG
Default	1
Effective	Only allowed to be modified in first start up

UDF

udf_initial_byte_array_length_for_memory_control

Name	udf_initial_byte_array_length_for_memory_control
Description	Used to estimate the memory usage of text fields in a UDF query. It is recommended to set this value to be slightly larger than the average length of all texts.
Type	Int32
Default	48
Effective	After restarting system

udf_memory_budget_in_mb

Name	udf_memory_budget_in_mb
Description	How much memory may be used in ONE UDF query (in MB). The upper limit is 20% of allocated memory for read.
Type	Float
Default	30.0
Effective	After restarting system

udf_reader_transformer_collector_memory_proportion

Name	udf_reader_transformer_collector_memory_proportion
Description	UDF memory allocation ratio for reader, transformer and collector. The parameter form is a : b : c, where a, b, and c are integers.
Type	String
Default	1:1:1
Effective	After restarting system

udf_root_dir

Name	udf_root_dir
Description	Root directory of UDF
Type	String
Default	ext/udf(Windows:ext\udf)
Effective	After restarting system

SELECT-INTO

select_into_insert_tablet_plan_row_limit

Name	select_into_insert_tablet_plan_row_limit
Description	The maximum number of rows that can be processed in insert-tablet-plan when executing select-into statements. When <= 0, use 10000.
Type	Int32
Default	10000
Effective	Trigger

concurrent_window_evaluation_thread

Name	concurrent_window_evaluation_thread
Description	How many threads can be used for evaluating sliding windows. When <= 0, use CPU core number.
Type	Int32
Default	The number of CPU cores
Effective	After restarting system

max_pending_window_evaluation_tasks

Name	max_pending_window_evaluation_tasks
Description	Maximum number of window evaluation tasks that can be pending for execution. When <= 0, the value is 64 by default.
Type	Int32
Default	64
Effective	After restarting system

Continuous Query

continuous_query_execution_thread

Name	continuous_query_execution_thread
Description	How many threads will be set up to perform continuous queries
Type	Int32
Default	max(1, the / 2)
Effective	After restarting system

max_pending_continuous_query_tasks

continuous_query_min_every_interval

Name	continuous_query_min_every_interval
Description	Minimum every interval to perform continuous query.
Type	duration
Default	1s
Effective	After restarting system

GC log is off by default. For performance tuning, you may want to collect the GC info.

To enable GC log, just add a parameter “printgc” when you start the server.

sbin\start-server.bat printgc

Config Manual