Help Center/ GaussDB(DWS)/ Standard Data Warehouse (8.1.3.x)/ GUC Parameters of the GaussDB(DWS) Database/ Developer Operations
Updated on 2024-12-19 GMT+08:00
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Developer Operations

enable_light_colupdate

Parameter description: Specifies whether to enable the lightweight column-store update.

Type: USERSET

Value range: Boolean

  • on indicates that the lightweight column-store update is enabled.
  • off indicates that the lightweight column-store update is disabled.

Default value: off

enable_fast_query_shipping

Parameter description: Specifies whether to use the distributed framework for a query planner.

Type: USERSET

Value range: Boolean

  • on indicates that execution plans are generated on CNs and DNs separately.
  • off indicates that the distributed framework is used. Execution plans are generated on CNs and then sent to DNs for execution.

Default value: on

enable_trigger_shipping

Parameter description: Specifies whether the trigger can be pushed to DNs for execution.

Type: USERSET

Value range: Boolean

  • on indicates that the trigger can be pushed to DNs for execution.
  • off indicates that the trigger cannot be pushed to DNs. It must be executed on the CN.

Default value: on

enable_remotejoin

Parameter description: Specifies whether JOIN operation plans can be delivered to DNs for execution.

Type: USERSET

Value range: Boolean

  • on indicates that JOIN operation plans can be delivered to DNs for execution.
  • off indicates that JOIN operation plans cannot be delivered to DNs for execution.

Default value: on

enable_remotegroup

Parameter description: Specifies whether the execution plans of GROUP BY and AGGREGATE can be delivered to DNs for execution.

Type: USERSET

Value range: Boolean

  • on indicates that the execution plans of GROUP BY and AGGREGATE can be delivered to DNs for execution.
  • off indicates that the execution plans of GROUP BY and AGGREGATE cannot be delivered to DNs for execution.

Default value: on

enable_remotelimit

Parameter description: Specifies whether the execution plan specified in the LIMIT clause can be pushed down to DNs for execution.

Type: USERSET

Value range: Boolean

  • on indicates that the execution plan specified in the LIMIT clause can be pushed down to DNs for execution.
  • off indicates that the execution plan specified in the LIMIT clause cannot be delivered to DNs for execution.

Default value: on

enable_limit_stop

Parameter description: Specifies whether the early stop optimization is enabled for LIMIT statements. For a LIMIT n statement, if early stop is used, the CN requests the DN to end the execution after receiving n pieces of data. This method is applicable to complex queries with LIMIT. This parameter is supported only by 8.1.3.320 and later cluster versions.

Type: USERSET

Value range: Boolean

  • on indicates that early stop is enabled for LIMIT statements.
  • off indicates that early stop is disabled for LIMIT statements.

Default value: on

enable_remotesort

Parameter description: Specifies whether the execution plan of the ORDER BY clause can be delivered to DNs for execution.

Type: USERSET

Value range: Boolean

  • on indicates that the execution plan of the ORDER BY clause can be delivered to DNs for execution.
  • off indicates that the execution plan of the ORDER BY clause cannot be delivered to DNs for execution.

Default value: on

enable_join_pseudoconst

Parameter description: Specifies whether joining with the pseudo constant is allowed. A pseudo constant indicates that the variables on both sides of a join are identical to the same constant.

Type: USERSET

Value range: Boolean

  • on indicates that joining with the pseudo constant is allowed.
  • off indicates that joining with the pseudo constant is not allowed.

Default value: off

cost_model_version

Parameter description: Specifies the model used for cost estimation in the application scenario. This parameter affects the distinct estimation of the expression, HashJoin cost model, estimation of the number of rows, distribution key selection during redistribution, and estimation of the number of aggregate rows.

Type: USERSET

Value range: 0, 1, or 2

  • 0 indicates that the original cost estimation model is used.
  • 1 indicates that the enhanced distinct estimation of the expression, HashJoin cost estimation model, estimation of the number of rows, distribution key selection during redistribution, and estimation of the number of aggregate rows are used on the basis of 0.
  • 2 indicates that the ANALYZE sampling algorithm with better randomicity is used on the basis of 1 to improve the accuracy of statistics collection.

Default value: 1

debug_assertions

Parameter description: Specifies whether to enable various assertion checks. This parameter assists in debugging. If you are experiencing strange problems or crashes, set this parameter to on to identify programming defects. To use this parameter, the macro USE_ASSERT_CHECKING must be defined (through the configure option --enable-cassert) during the GaussDB(DWS) compilation.

Type: USERSET

Value range: Boolean

  • on indicates that various assertion checks are enabled.
  • off indicates that various assertion checks are disabled.

This parameter is set to on by default if GaussDB(DWS) is compiled with various assertion checks enabled.

Default value: off

distribute_test_param

Parameter description: Specifies whether the embedded test stubs for testing the distribution framework take effect. In most cases, developers embed some test stubs in the code during fault injection tests. Each test stub is identified by a unique name. The value of this parameter is a triplet that includes three values: thread level, test stub name, and error level of the injected fault. The three values are separated by commas (,).

Type: USERSET

Value range: a string indicating the name of any embedded test stub.

Default value: -1, default, default

enable_crc_check

Parameter description: Specifies whether to enable data checks. Check information is generated when table data is written and is checked when the data is read. You are not advised to modify the settings.

Type: POSTMASTER

Value range: Boolean

  • on indicates that data checks are enabled.
  • off indicates that data checks are disabled.

Default value: on

If CRC is enabled, all data on a page must be written to WALs when hint bits of tuples on the page are modified for the first time after a checkpoint. This deteriorates the performance of the first query after the checkpoint.

ignore_checksum_failure

Parameter description: Sets whether to ignore check failures (but still generates an alarm) and continues reading data. This parameter is valid only when enable_crc_check is set to on. Continuing reading data may result in breakdown, damaged data being transferred or hidden, failure of data recovery from remote nodes, or other serious problems. You are not advised to modify the settings.

Type: SUSET

Value range: Boolean

  • on indicates that data check errors are ignored.
  • off indicates that data check errors are reported.

Default value: off

enable_colstore

Parameter description: Specifies whether to create a table as a column-store table by default when no storage method is specified. The value for each node must be the same. This parameter is used for tests. Users are not allowed to enable it.

Type: SUSET

Value range: Boolean

Default value: off

enable_force_vector_engine

Parameter description: Specifies whether to forcibly generate vectorized execution plans for a vectorized execution operator if the operator's child node is a non-vectorized operator. When this parameter is set to on, vectorized execution plans are forcibly generated. When enable_force_vector_engine is enabled, no matter it is a row-store table, column-store table, or hybrid row-column store table, if the plantree does not contain scenarios that do not support vectorization, the vectorized executor is forcibly used.

Type: USERSET

Value range: Boolean

Default value: off

enable_csqual_pushdown

Parameter description: Specifies whether to deliver filter criteria for a rough check during query.

Type: USERSET

Value range: Boolean

  • on indicates that a rough check is performed with filter criteria delivered during query.
  • off indicates that a rough check is performed without filter criteria delivered during query.

Default value: on

explain_dna_file

Parameter description: Specifies the name of a CSV file exported when explain_perf_mode is set to run.

Type: USERSET

The value of this parameter must be an absolute path plus a file name with the extension .csv.

Value range: a string

Default value: NULL

explain_perf_mode

Parameter description: Specifies the display format of the explain command.

Type: USERSET

Value range: normal, pretty, summary, and run

  • normal indicates that the default printing format is used.
  • pretty indicates that the optimized display mode of GaussDB(DWS) is used. A new format contains a plan node ID, directly and effectively analyzing performance.
  • summary indicates that the analysis result based on such information is printed in addition to the printed information in the format specified by pretty.
  • run indicates that in addition to the printed information specified by summary, the database exports the information as a CSV file.

Default value: pretty

join_num_distinct

Parameter description: Controls the default distinct value of the join column or expression in application scenarios.

Type: USERSET

Value range: a double-precision floating point number greater than or equal to -100. Decimals may be truncated when displayed on clients.

  • If the value is greater than 0, the value is used as the default distinct value.
  • If the value is greater than or equal to -100 and less than 0, it means the percentage used to estimate the default distinct value.
  • If the value is 0, the default distinct value is 200.

Default value: -20

qual_num_distinct

Parameter description: Controls the default distinct value of the filter column or expression in application scenarios.

Type: USERSET

Value range: a double-precision floating point number greater than or equal to -100. Decimals may be truncated when displayed on clients.

  • If the value is greater than 0, the value is used as the default distinct value.
  • If the value is greater than or equal to -100 and less than 0, it means the percentage used to estimate the default distinct value.
  • If the value is 0, the default distinct value is 200.

Default value: 200

trace_notify

Parameter description: Specifies whether to generate a large amount of debugging output for the LISTEN and NOTIFY commands. client_min_messages or log_min_messages must be DEBUG1 or lower so that such output can be recorded in the logs on the client or server separately.

Type: USERSET

Value range: Boolean

  • on indicates that the function is enabled.
  • off indicates that the function is disabled.

Default value: off

trace_sort

Parameter description: Specifies whether to display information about resource usage during sorting operations in logs. This parameter is available only when the macro TRACE_SORT is defined during the GaussDB(DWS) compilation. However, TRACE_SORT is currently defined by default.

Type: USERSET

Value range: Boolean

  • on indicates that the function is enabled.
  • off indicates that the function is disabled.

Default value: off

zero_damaged_pages

Parameter description: Specifies whether to detect a damaged page header that causes GaussDB(DWS) to report an error, aborting the current transaction.

Type: SUSET

Value range: Boolean

  • on indicates that the function is enabled.
  • off indicates that the function is disabled.
  • Setting this parameter to on causes the system to report a warning, pad the damaged page with zeros, and then continue with subsequent processing. This behavior will damage data, that is, all rows on the damaged page. However, it allows you to bypass the error and retrieve rows from any undamaged pages that are present in the table. Therefore, it is useful for restoring data that is damaged due to a hardware or software error. In most cases, you are not advised to set this parameter to on unless you do not want to restore data from the damaged pages of a table.
  • For a column-store table, the system will skip the entire CU and then continue processing. The supported scenarios include the CRC check failure, magic check failure, and incorrect CU length.

Default value: off

replication_test

Parameter description: Specifies whether to enable internal testing on the data replication function.

Type: USERSET

Value range: Boolean

  • on indicates that internal testing on the data replication function is enabled.
  • off indicates that internal testing on the data replication function is disabled.

Default value: off

cost_param

Parameter description: Controls use of different estimation methods in specific customer scenarios, allowing estimated values approximating to onsite values. This parameter can control various methods simultaneously by performing AND (&) operations on the bit for each method. A method is selected if its value is not 0.

If cost_param & 1 is not set to 0, an improvement mechanism is selected for calculating a non-equi join selection rate, which is more accurate in estimation of self-join (join between two same tables). In V300R002C00 and later, cost_param & 1=0 is not used. That is, an optimized formula is selected for calculation.

When cost_param & 2 is set to a value other than 0, the selection rate is estimated based on multiple filter criteria. The lowest selection rate among all filter criteria, but not the product of the selection rates for two tables under a specific filter criterion, is used as the total selection rate. This method is more accurate when a close correlation exists between the columns to be filtered.

When cost_param & 4 is not 0, the selected debugging model is not recommended when the stream node is evaluated.

When cost_param & 16 is not 0, the model between fully correlated and fully uncorrelated models is used to calculate the comprehensive selection rate of two or more filtering conditions or join conditions. If there are many filtering conditions, the strongly-correlated model is preferred.

Type: USERSET

Value range: an integer ranging from 1 to INT_MAX

Default value: 16

convert_string_to_digit

Parameter description: Specifies the implicit conversion priority, which determines whether to preferentially convert strings into numbers.

Type: USERSET

Value range: Boolean

  • on indicates that strings are preferentially converted into numbers.
  • off indicates that strings are not preferentially converted into numbers.

Default value: on

Modify this parameter only when absolutely necessary because the modification will change the rule for converting internal data types and may cause unexpected results.

nls_timestamp_format

Parameter description: Specifies the default timestamp format.

Type: USERSET

Value range: a string

Default value: DD-Mon-YYYY HH:MI:SS.FF AM

enable_partitionwise

Parameter description: Specifies whether to select an intelligent algorithm for joining partitioned tables.

Type: USERSET

Value range: Boolean

  • on indicates that an intelligent algorithm is selected.
  • off indicates that an intelligent algorithm is not selected.

Default value: off

enable_partition_dynamic_pruning

Parameter description: Specifies whether dynamic pruning is enabled during partition table scanning.

Type: USERSET

Value range: Boolean

  • on: enable
  • off: disable

Default value: on

max_user_defined_exception

Parameter description: Specifies the maximum number of exceptions. The default value cannot be changed.

Type: USERSET

Value range: an integer

Default value: 1000

datanode_strong_sync

Parameter description: This parameter no longer takes effect.

Type: USERSET

Value range: Boolean

  • on indicates that forcible synchronization between stream nodes is enabled.
  • off indicates that forcible synchronization between stream nodes is disabled.

Default value: off

enable_global_stats

Parameter description: Specifies the current statistics mode. This parameter is used to compare global statistics generation plans and the statistics generation plans for a single DN. This parameter is used for tests. Users are not allowed to enable it.

Type: SUSET

Value range: Boolean

  • on or true indicates the global statistics mode.
  • off or false indicates the single-DN statistics mode.

Default value: on

enable_fast_numeric

Parameter description: Specifies whether to enable optimization for numeric data calculation. Calculation of numeric data is time-consuming. Numeric data is converted into int64- or int128-type data to improve numeric data calculation performance.

Type: USERSET

Value range: Boolean

  • on/true indicates that optimization for numeric data calculation is enabled.
  • off/false indicates that optimization for numeric data calculation is disabled.

Default value: on

enable_row_fast_numeric

Parameter description: Specifies the format in which numeric data in a row-store table is spilled to disks.

Type: USERSET

Value range: Boolean

  • on/true indicates that numeric data in a row-store table is spilled to disks in bigint format.
  • off/false indicates that numeric data in a row-store table is spilled to disks in the original format.

If this parameter is set to on, you are advised to enable enable_force_vector_engine to improve the query performance of large data sets. However, compared with the original format, there is a high probability that the bigint format occupies more disk space. For example, the TPC-H test set occupies about 7% more space (reference value, may vary depending on the environment).

Default value: off

rewrite_rule

Parameter description: Specifies the rewriting rule for enabled optional queries. Some query rewriting rules are optional. Enabling them cannot always improve query efficiency. In a specific customer scenario, you can set the query rewriting rules through the GUC parameter to achieve optimal query efficiency.

This parameter can control the combination of query rewriting rules, for example, there are multiple rewriting rules: rule1, rule2, rule3, and rule4. To set the parameters, you can perform the following operations:

set rewrite_rule=rule1;          --Enable query rewriting rule rule1.
set rewrite_rule=rule2,rule3;    --Enable query rewriting rules rule2 and rule3.
set rewrite_rule=none;           --Disable all optional query rewriting rules.

Type: USERSET

Value range: a string

  • none: Does not use any optional query rewriting rules.
  • lazyagg: Uses the Lazy Agg query rewriting rules for eliminating aggregation operations in subqueries.
  • magicset: Uses the Magic Set query rewriting rules (from the main query to subqueries).
  • uniquecheck: Uses the Unique Check rewriting rule. (The scenario where the target column does not contain the expression sublink of the aggregate function can be improved. The function can be enabled only when the value of the target column is unique after the sublink is aggregated based on the associated column. This function is recommended to be used by optimization engineers.)
  • disablerep: Uses the function that prohibits pulling up sublinks of the replication table. (Disables sublink pull-up for the replication table.)
  • projection_pushdown: the Projection Pushdown rewriting rule (Removes columns that are not used by the parent query from the subquery).
  • or_conversion: the OR conversion rewriting rule (eliminates the association OR conditions that are inefficient to execute).
  • plain_lazyagg: Uses the Plain Lazy Agg query rewriting rule (eliminates aggregation operations in a single subquery). This option is supported only by clusters of version 8.1.3.100 or later.

Default value: magicset, or_conversion, projection_pushdown, and plain_lazyagg

enable_compress_spill

Parameter description: Specifies whether to enable the compression function of writing data to a disk.

Type: USERSET

Value range: Boolean

  • on/true indicates that optimization for writing data to a disk is enabled.
  • off/false indicates that optimization for writing data to a disk is disabled.

Default value: on

analysis_options

Parameter description: Specifies whether to enable function options in the corresponding options to use the corresponding location functions, including data verification and performance statistics. For details, see the options in the value range.

Type: USERSET

Value range: a string

  • LLVM_COMPILE indicates that the codegen compilation time of each thread is displayed on the explain performance page.
  • HASH_CONFLICT indicates that the log file in the pg_log directory of the DN process displays the hash table statistics, including the hash table size, hash chain length, and hash conflict information.
  • STREAM_DATA_CHECK indicates that a CRC check is performed on data before and after network data transmission.

Default value: off(ALL), which indicates that no location function is enabled.

resource_track_log

Parameter description: Specifies the log level of self-diagnosis. Currently, this parameter takes effect only in multi-column statistics.

Type: USERSET

Value range: a string

  • summary: Brief diagnosis information is displayed.
  • detail: Detailed diagnosis information is displayed.

Currently, the two parameter values differ only when there is an alarm about multi-column statistics not collected. If the parameter is set to summary, such an alarm will not be displayed. If it is set to detail, such an alarm will be displayed.

Default value: summary

hll_default_log2m

Parameter description: Specifies the number of buckets for HLL data. Using more buckets in HLL calculations leads to more precise and less deviated distinct value results. The deviation range is as follows: [–1.04/2log2m*1/2, +1.04/2log2m*1/2]

Type: USERSET

Value range: an integer ranging from 10 to 16

Default value: 11

hll_default_regwidth

Parameter description: Specifies the number of bits in each bucket for HLL data. A larger value indicates more memory occupied by HLL. hll_default_regwidth and hll_default_log2m determine the maximum number of distinct values that can be calculated by HLL. For details, see Table 1.

Type: USERSET

Value range: an integer ranging from 1 to 5

Default value: 5

Table 1 Maximum number of calculated distinct values determined by hll_default_log2m and hll_default_regwidth

log2m

regwidth = 1

regwidth = 2

regwidth = 3

regwidth = 4

regwidth = 5

10

7.4e+02

3.0e+03

4.7e+04

1.2e+07

7.9e+11

11

1.5e+03

5.9e+03

9.5e+04

2.4e+07

1.6e+12

12

3.0e+03

1.2e+04

1.9e+05

4.8e+07

3.2e+12

13

5.9e+03

2.4e+04

3.8e+05

9.7e+07

6.3e+12

14

1.2e+04

4.7e+04

7.6e+05

1.9e+08

1.3e+13

15

2.4e+04

9.5e+04

1.5e+06

3.9e+08

2.5e+13

hll_default_expthresh

Parameter description: Specifies the default threshold for switching from the explicit mode to the sparse mode.

Type: USERSET

Value range: an integer ranging from –1 to 7 –1 indicates the auto mode; 0 indicates that the explicit mode is skipped; a value from 1 to 7 indicates that the mode is switched when the number of distinct values reaches 2hll_default_expthresh.

Default value: –1

hll_default_sparseon

Parameter description: Specifies whether to enable the sparse mode by default.

Type: USERSET

Valid value: 0 and 1 0 indicates that the sparse mode is disabled by default. 1 indicates that the sparse mode is enabled by default.

Default value: 1

hll_max_sparse

Parameter description: Specifies the size of max_sparse.

Type: USERSET

Value range: an integer ranging from –1 to INT_MAX

Default value: –1

enable_compress_hll

Parameter description: Specifies whether to enable memory optimization for HLL.

Type: USERSET

Value range: Boolean

  • on or true indicates that memory optimization is enabled.
  • off or false indicates that memory optimization is disabled.

Default value: off

udf_memory_limit

Parameter description: Controls the maximum physical memory that can be used when each CN or DN executes UDFs.

Type: POSTMASTER

Value range: an integer ranging from 200 x 1024 to the value of max_process_memory and the unit is KB.

Default value: 0.05 * max_process_memory

FencedUDFMemoryLimit

Parameter description: Controls the virtual memory used by each fenced udf worker process.

Type: USERSET

Suggestion: You are not advised to set this parameter. You can set udf_memory_limit instead.

Value range: an integer. The unit can be KB, MB, or GB. 0 indicates that the memory is not limited.

Default value: 0

UDFWorkerMemHardLimit

Parameter description: Specifies the maximum value of fencedUDFMemoryLimit.

Type: POSTMASTER

Suggestion: You are not advised to set this parameter. You can set udf_memory_limit instead.

Value range: an integer. The unit can be KB, MB, or GB.

Default value: 1 GB

enable_pbe_optimization

Parameter description: Specifies whether the optimizer optimizes the query plan for statements executed in Parse Bind Execute (PBE) mode.

Type: USERSET

Value range: Boolean

  • on indicates that the optimizer optimizes the query plan.
  • off indicates that the optimization does not optimize the query plan.

Default value: on

enable_light_proxy

Parameter description: Specifies whether the optimizer optimizes the execution of simple queries on CNs.

Type: USERSET

Value range: Boolean

  • on indicates that the optimizer optimizes the execution.
  • off indicates that the optimization does not optimize the execution.

Default value: on

checkpoint_flush_after

Parameter description: Specifies the number of consecutive disk pages that the checkpointer writer thread writes before asynchronous flush. In GaussDB(DWS), the size of a disk page is 8 KB.

Type: SIGHUP

Value range: an integer ranging from 0 to 256. 0 indicates that the asynchronous flush function is disabled. For example, if the value is 32, the checkpointer thread continuously writes 32 disk pages (that is, 32 x 8 = 256 KB) before asynchronous flush.

Default value: 32

enable_parallel_ddl

Parameter description: Controls whether multiple CNs can concurrently perform DDL operations on the same database object.

Type: USERSET

Value range: Boolean

  • on indicates that DDL operations can be performed safely and that no distributed deadlock occurs.
  • off indicates that DDL operations cannot be performed safely and that distributed deadlocks may occur.

Default value: on

gc_fdw_verify_option

Parameter description: Specifies whether to enable the logic for verifying the number of rows in a result set in the collaborative analysis. This parameter is supported by version 8.1.3.310 or later clusters.

Type: USERSET

Value range: Boolean

  • on indicates that the logic for verifying the number of rows in the result set is enabled. The SELECT COUNT statement is used to obtain the expected number of rows and compare it with the actual number of rows.
  • off indicates that the logic for verifying the number of rows in the result set is disabled and only the required result set is obtained.

Default value: on

  • If this parameter is enabled, the performance deteriorates slightly. In performance-sensitive scenarios, you can disable this parameter to improve the performance.
  • If an exception is thrown during the result set row verification. You can set log_min_messages=debug1 and logging_module='on(COOP_ANALYZE)' to obtain the collaborative analysis logs.

show_acce_estimate_detail

Parameter description: When the GaussDB(DWS) cluster is accelerated (acceleration_with_compute_pool is set to on), specifies whether the EXPLAIN statement displays the evaluation information about execution plan pushdown to computing Node Groups. The evaluation information is generally used by O&M personnel during maintenance, and it may affect the output display of the EXPLAIN statement. Therefore, this parameter is disabled by default. The evaluation information is displayed only if the verbose option of the EXPLAIN statement is enabled.

Type: USERSET

Value range: Boolean

  • on indicates that the evaluation information is displayed in the output of the EXPLAIN statement.
  • off indicates that the evaluation information is not displayed in the output of the EXPLAIN statement.

Default value: off

support_batch_bind

Parameter description: Specifies whether to batch bind and execute PBE statements through interfaces such as JDBC, ODBC, and Libpq.

Type: SIGHUP

Value range: Boolean

  • on indicates that batch binding and execution are used.
  • off indicates that batch binding and execution are not used.

Default value: on