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Computing layer parameters

Last Updated: Dec 09, 2021

PolarDB-X uses an architecture in which storage is decoupled from computing. The following table describes common compute node parameters. You can configure some compute node parameters in the PolarDB-X console.

Parameter

Restarted

Default value

Valid value

Description

PLAN_CACHE

No

TRUE

[TURE|FALSE]

Specifies whether to enable the plan cache.

ENABLE_RECYCLEBIN

No

FALSE

[TURE|FALSE]

Specifies whether to enable the recycle bin feature.

SHOW_TABLES_CACHE

No

FALSE

[TURE|FALSE]

Specifies whether to cache the results returned by SHOW TABLES statements.

MERGE_CONCURRENT

No

FALSE

[TURE|FALSE]

Specifies whether to enable the massively parallel processing (MPP) mode. The value of this parameter has an impact on the degree of parallelism (DOP) of all simple queries that are pushed down and DDL statements.

MERGE_UNION

No

FALSE

[TURE|FALSE]

Specifies whether to use UNION operators to optimize physical SQL statements and whether to serially execute the physical SQL statements that are pushed down. If this parameter is set to TRUE, UNION operators are not used to optimize physical SQL statements and physical SQL statements that are pushed down are serially executed. Default value: FALSE.

MERGE_UNION_SIZE

No

-1

[0-10000]

The number of physical SQL statements merged by using the UNION operator. By default, the number of physical SQL statements is automatically calculated based on the number of available connections in the connection pool.

TABLE_META_CACHE_EXPIRE_TIME

No

300

[0-180000]

The time when metadata expires.

COLUMN_LABEL_INSENSITIVE

No

TRUE

[FALSE|TRUE]

Specifies whether returned columns are case-sensitive.

RECORD_SQL

No

TRUE

[FALSE|TRUE]

Specifies whether to enable the log audit feature.

SOCKET_TIMEOUT

No

900000

[0~3600000]

The time-out period of physical SQL statements.

TRANSACTION_POLICY

No

TSO

[XA|TSO|TSO_READONLY]

The transaction policy.

SHARE_READ_VIEW

No

FALSE

[TRUE|FALSE]

Specifies whether to share the read view.

ENABLE_TRX_SINGLE_SHARD_OPTIMIZATION

No

TRUE

[TRUE|FALSE]

Specifies whether to optimize a single shard for the transaction.

GET_TSO_TIMEOUT

No

10

[1-1800]

Specifies whether to query the timeout period of the Timestamp Oracle (TSO) timestamp.

MAX_TRX_DURATION

No

28800

[1-180000]

The timeout period of the transaction that is not committed.

TRANSACTION_ISOLATION

No

REPEATABLE_READ

[READ_UNCOMMITTED|READ_COMMITTED|REPEATABLE_READ|SERIALIZABLE]

The transaction isolation level.

GROUP_CONCURRENT_BLOCK

No

TRUE

[TRUE|FALSE]

Specifies whether to use the execution policy at the database shard level when the mode is not the MPP mode.

SEQUENTIAL_CONCURRENT_POLICY

No

FALSE

[TRUE|FALSE]

Specifies whether to use the execution policy for a single instance that processes concurrent requests when the mode is not the MPP mode.

DML_SKIP_DUPLICATE_CHECK_FOR_PK

No

TRUE

[TRUE|FALSE]

Specifies whether to skip the check on primary key conflicts when DML statements are executed.

DML_SKIP_CRUCIAL_ERR_CHECK

No

FALSE

[TRUE|FALSE]

Specifies whether transactions for which DML statement errors are reported can be committed when DML statements are executed.

DML_USE_RETURNING

No

TRUE

[TRUE|FALSE]

Specifies whether to use returning clauses to optimize DML statements.

BROADCAST_DML

No

FALSE

[TRUE|FALSE]

Specifies whether data can be written to broadcast tables on the node where the broadcast tables are stored.

SEQUENCE_STEP

No

10000

[1-10000000]

The SEQUENCE step size. Default value: 100,000.

MERGE_DDL_TIMEOUT

No

0

[1-10000000]

The timeout period of the physical DDL connection. Default value: 0. The default value indicates that the connection does not time out.

MERGE_DDL_CONCURRENT

No

FALSE

[FALSE|TRUE]

Specifies whether to use the MPP mode for DDL statements. By default, DDL statements are concurrently executed at the database level.

SLOW_SQL_TIME

No

1000

[1-180000]

The threshold value for slow SQL queries.

LOAD_DATA_BATCH_INSERT_SIZE

No

1024

[1-180000]

The number of records that the LOAD DATA statement inserts at a time.

LOAD_DATA_CACHE_BUFFER_SIZE

No

60

[1-180000]

The size of the cache where data about LOAD DATA statements is stored. Default value: 60. Unit: MB. In most cases, this parameter is used for throttling.

MAX_ALLOWED_PACKET

No

16777216

[4194304-33554432]

The size of the maximum packet.

KILL_CLOSE_STREAM

No

FALSE

[FALSE|TRUE]

Specifies whether to disable the connections between compute nodes and data nodes when the number of queried records reaches the upper limit.

ALLOW_SIMPLE_SEQUENCE

No

FALSE

[FALSE|TRUE]

Specifies whether to use simple sequences.

MAX_PARAMETERIZED_SQL_LOG_LENGTH

No

5000

[1-1000000]

The maximum size of the log generated for parameterized SQL statements.

FORBID_EXECUTE_DML_ALL

No

TRUE

[TRUE|FALSE]

Specifies whether to disable updates or deletions for full tables.

GROUP_SEQ_CHECK_INTERVAL

Yes

60

[1-36000]

The interval at which inserted explicit values are checked. Unit: seconds.

JOIN_BLOCK_SIZE

Yes

300

[1-100000]

The number of values returned by the IN operator when the Batched Key Access (BKA) join algorithm is used and IN values are not dynamically pruned.

LOOKUP_JOIN_MAX_BATCH_SIZE

Yes

6400

[1-100000]

The maximum number of values returned by the IN operator when the BKA join algorithm is used.

LOOKUP_JOIN_MIN_BATCH_SIZE

Yes

100

[1-100000]

The minimum number of values returned by the IN operator when the BKA join algorithm is used.

PURGE_TRANS_INTERVAL

Yes

300

[1-180000]

The interval at which transaction logs are cleared.

PURGE_TRANS_BEFORE

Yes

1800

[1-180000]

The time period before which transaction logs are cleared.

ENABLE_BACKGROUND_STATISTIC_COLLECTION

No

TRUE

[TRUE|FALSE]

Specifies whether statistics can be collected.

GENERAL_DYNAMIC_SPEED_LIMITATION

No

-1

[-1-10000000]

Specifies whether to limit the speed at which data is backfilled and verified. The default value -1 indicates that the speed is limited.

PARALLELISM

No

-1

[1-1024]

The DOP of the symmetric multiprocessing (SMP) mode. The value is calculated based on specifications.

LOGICAL_DB_TIME_ZONE

No

SYSTEM

[SYSTEM|±HH:mm]

The time zone of the database.

MPP_PARALLELISM

No

-1

[1-1024]

The DOP of the MPP mode. The value is calculated based on database specifications.

DATABASE_PARALLELISM

No

0

[0-1024]

The number of SQL statements that are executed at the same time for a single query on a data node.

POLARDBX_PARALLELISM

No

0

[0-1024]

The maximum DOP for a single query on a compute node. The default value is the number of CPU cores.

MPP_METRIC_LEVEL

No

3

[0|1|2|3]

The level of collected statistics in the process of computing data. A higher level indicates the higher granularity of collected statistics.

ENABLE_COMPLEX_DML_CROSS_DB

No

TRUE

[TRUE|FALSE]

Specifies whether complex DML statements can be executed across databases.

PER_QUERY_MEMORY_LIMIT

Yes

-1

[-1-9223372036854775807]

The maximum size of the memory pool for queries. By default, the maximum size of the memory pool for queries is one third the size of the global connection pool.

ENABLE_SPILL

No

FALSE

[FALSE|TRUE]

Specifies whether to flush temporary tables to the disk.

CONN_POOL_MIN_POOL_SIZE

No

20

[0-10]

The minimum number of connections to physical database shards.

CONN_POOL_MAX_POOL_SIZE

No

60

[1-1600]

The maximum number of connections to physical database shards.

CONN_POOL_MAX_WAIT_THREAD_COUNT

No

0

[-1-8192]

The maximum number of pending connections to a single database shard (Apach Druid)

CONN_POOL_IDLE_TIMEOUT

No

30

[1-60]

The timeout period of physical idle connections.

CONN_POOL_BLOCK_TIMEOUT

No

5000

[1000-60000]

The maximum period of time that is required to obtain a connection from the physical connection pool.

CONN_POOL_XPROTO_MAX_POOLED_SESSION_PER_INST

No

512

[1-8192]

The maximum number of cached sessions on a single storage node. The cached sessions are transmitted over proprietary protocols.

XPROTO_MAX_DN_CONCURRENT

No

500

[1-8192]

The maximum number of concurrent requests on a single storage node. The requests are transmitted over proprietary protocols.

XPROTO_MAX_DN_WAIT_CONNECTION

No

32

[1-8192]

The maximum number of pending requests on a single storage node. The requests are transmitted over private protocols.

MERGE_SORT_BUFFER_SIZE

No

2048

[1024-81920]

The cache size that is used to merge and sort data at the TableScan layer. Default value: 2 MB.

WORKLOAD_TYPE

No

[AP|TP]

Specifies the type of the query workload. By default, the workload type is intelligently identified based on costs.

EXECUTOR_MODE

No

[MPP|TP_LOCAL|AP_LOCAL]

Specifies the mode in which queries are run. By default, the mode is selected based on the query workload type.

ENABLE_MASTER_MPP

No

FALSE

[TRUE|FALSE]

Specifies whether to enable the MPP mode on the primary instance.

LOOKUP_JOIN_BLOCK_SIZE_PER_SHARD

Yes

50

[1-100000]

The number of values returned by the IN operator on a single shard when the BKA join algorithm is used and IN values is pruned.

ENABLE_RUNTIME_FILTER

No

TRUE

[TRUE|FALSE]

Specifies whether to enable the runtime filter.

FEEDBACK_WORKLOAD_AP_THRESHOLD

No

FALSE

[TRUE|FALSE]

Specifies whether to enable the HTAP FEEDBACK feature for analytical processing (AP) queries.

FEEDBACK_WORKLOAD_TP_THRESHOLD

No

FALSE

[TRUE|FALSE]

Specifies whether to enable the HTAP FEEDBACK feature for transaction processing (TP) queries.

MASTER_READ_WEIGHT

No

-1

[0-100]

The weight of rule-based read/write splitting.

SHOW_ALL_PARAMS

No

FALSE

[TRUE|FALSE]

Specifies whether to display all parameters.

ENABLE_SET_GLOBAL

No

FALSE

[TRUE|FALSE]

Specifies whether to enable SET GLOBAL statements.

FORCE_READ_OUTSIDE_TX

No

FALSE

[TRUE|FALSE]

Specifies whether to forcibly enable multiple connections on a database shard in a transaction.

ENABLE_COROUTINE

Yes

FALSE

[TRUE|FALSE]

Specifies whether to enable Wisp coroutine.

TRUNCATE_TABLE_WITH_GSI

No

FALSE

[TRUE|FALSE]

Specifies whether TRUNCATE statements can contain global secondary index (GSI) tables.

DDL_ON_GSI

No

FALSE

[TRUE|FALSE]

Specifies whether DDL statements can be executed on GSI tables.

DML_ON_GSI

No

FALSE

[TRUE|FALSE]

Specifies whether DML statements can be executed on GSI tables.

ENABLE_HASH_JOIN

No

TRUE

[TRUE|FALSE]

Specifies whether hash join nodes can be generated when execution plans are optimized.

ENABLE_BKA_JOIN

No

TRUE

[TRUE|FALSE]

Specifies whether BKA join nodes can be generated when execution plans are optimized.

ENABLE_NL_JOIN

No

TRUE

[TRUE|FALSE]

Specifies whether nested loop join nodes can be generated when execution plans are optimized.

ENABLE_SEMI_NL_JOIN

No

TRUE

[TRUE|FALSE]

Specifies whether semi joins can be converted to nested loop joins when execution plans are optimized.

ENABLE_SEMI_HASH_JOIN

No

TRUE

[TRUE|FALSE]

Specifies whether semi joins can be converted to hash joins when execution plans are optimized.

ENABLE_SEMI_BKA_JOIN

No

TRUE

[TRUE|FALSE]

Specifies whether semi joins can be converted to BKA joins when execution plans are optimized.

ENABLE_SEMI_SORT_MERGE_JOIN

No

TRUE

[TRUE|FALSE]

Specifies whether semi joins can be converted to merge joins when execution plans are optimized.

ENABLE_MATERIALIZED_SEMI_JOIN

No

TRUE

[TRUE|FALSE]

Specifies whether semi joins can be converted to materialized view joins when execution plans are optimized.

ENABLE_SEMI_JOIN_REORDER

No

TRUE

[TRUE|FALSE]

Specifies whether semi joins can be used for Cost-Based Optimization (CBO) recorder optimization when execution plans are optimized.

ENABLE_HASH_AGG

No

TRUE

[TRUE|FALSE]

Specifies whether HashAgg nodes can be generated when execution plans are optimized.

ENABLE_PARTIAL_AGG

No

TRUE

[TRUE|FALSE]

Specifies whether the aggregate function can be called in two phases when execution plans are optimized.

ENABLE_SORT_AGG

No

TRUE

[TRUE|FALSE]

Specifies whether SortAgg nodes can be generated when execution plans are optimized.

ENABLE_PUSH_PROJECT

No

TRUE

[TRUE|FALSE]

Specifies whether projection pushdown is allowed when execution plans are optimized.

ENABLE_PUSH_JOIN

No

TRUE

[TRUE|FALSE]

Specifies whether a join operation can be pushed down when execution plans are optimized.

ENABLE_PUSH_AGG

No

TRUE

[TRUE|FALSE]

Specifies whether an aggregate operation can be pushed down when execution plans are optimized.

ENABLE_CBO_PUSH_AGG

No

TRUE

[TRUE|FALSE]

Specifies whether aggregate functions can pass though join operations when execution plans are optimized.

ENABLE_PUSH_SORT

No

TRUE

[TRUE|FALSE]

Specifies whether a sort operation can be pushed down when execution plans are optimized.

ENABLE_STATISTIC_FEEDBACK

No

TRUE

[TRUE|FALSE]

Specifies whether corrected feedback for statistical information can be collected.

ENABLE_CBO_PUSH_JOIN

No

TRUE

[TRUE|FALSE]

Specifies whether a pass-through query that is used to perform join operations can be optimized when execution plans are optimized.

ENABLE_SORT_JOIN_TRANSPOSE

No

TRUE

[TRUE|FALSE]

Specifies whether SORT functions can be included in pass-through queries that are used to perform join operations when execution plans are optimized.

CHUNK_SIZE

No

1024

[1-10240]

The size of data that the executor computes each time.

ENABLE_SORT_MERGE_JOIN

No

TRUE

[TRUE|FALSE]

Specifies whether to prevent merge join nodes from being generated when execution plans are optimized.

ENABLE_BKA_PRUNING

No

TRUE

[TRUE|FALSE]

Specifies whether to enable the pruning feature of BKA joins.

ENABLE_SPM

No

TRUE

[TRUE|FALSE]

Specifies whether to manage execution plans.

ENABLE_EXPRESSION_VECTORIZATION

No

TRUE

[TRUE|FALSE]

Specifies whether to enable vectorization for expressions.

FORCE_DDL_ON_LEGACY_ENGINE

No

TRUE

[TRUE|FALSE]

Specifies whether to enable the new DDL engine.

PURE_ASYNC_DDL_MODE

No

FALSE

[TRUE|FALSE]

Specifies whether to execute DDL statements in asynchronous mode. If this parameter is set to TRUE, the client returns a response when a DDL request is received. You can execute the show [full] ddl statement to view the status of the DDL statement.

DDL_JOB_REQUEST_TIMEOUT

No

90000

[1-9223372036854775807]

The threshold value for the maximum duration in which the DDL statement can be executed. When the threshold value is exceeded, the DDL statement fails. Default value: 25. Unit: days.

LOGICAL_DDL_PARALLELISM

No

1

[1-10240]

The DOP of logical DDL statements. If this parameter is set to 1, the DDL job is serially executed.

ENABLE_BROADCAST_RANDOM_READ

No

TRUE

[TRUE|FALSE]

Specifies whether to enable random read optimization for broadcast tables.