V$OB_MEMORY|V4.2.5|OceanBase Database| docs|Distributed Database

V$OB_MEMORY

Last Updated：2026-07-16 07:53:03 Updated

The view name has been changed from V$MEMORY to V$OB_MEMORY since V4.0.0.
This view is currently supported only in MySQL-compatible mode. In Oracle-compatible mode, the query result will be empty.

Overview

Displays the memory statistics of the current tenant on the current node.

Columns

Field	Type	Nullable	Description
CON_ID	NUMBER(38)	NO	Tenant ID
SVR_IP	VARCHAR2(46)	NO	Server IP Address
SVR_PORT	NUMBER(38)	NO	Server Port Number
CTX_NAME	VARCHAR2(256)	NO	Name of the CTX to Which Memory Belongs
MOD_NAME	VARCHAR2(256)	NO	Name of the module to which the memory belongs
COUNT	NUMBER	NO	The difference between the allocated and freed memory, indicating the number of memory units currently in use by this module.
HOLD	NUMBER	NO	The memory size currently occupied by this module
USED	NUMBER	NO	The memory usage of the module, in bytes.

CTX_NAME field values

The following table describes the common memory CTX names and their meanings:

CTX_NAME	Description
DEFAULT_CTX_ID	Indicates the context ID of the unpartitioned memory collection.
MEMSTORE_CTX_ID	Represents the user's MemTable data context ID.
TRANS_CTX_MGR_ID	Transaction Context ID
PLAN_CACHE_CTX_ID	Execution plan cache context ID.
GLIBC	Indicates the memory allocated using the Glibc Malloc interface.
CO_STACK	Represents the memory of the thread execution stack.
KVSTORE_CACHE_ID	Represents the dynamic scalable cache ID.
META_OBJ_CTX_ID	Represents the memory for storing metadata, such as macroblock meta.
TX_CALLBACK_CTX_ID	Represents the transaction callback context ID. It is used to record some modifications during transaction execution, so that corresponding data can be found for operations during transaction commit or rollback.
LOB_CTX_ID	Indicates the allocator ID in the OBlobManager.
PS_CACHE_CTX_ID	denotes`PREPARE stmt_name FROM preparable_stmt`Cache ID of the statement.
TX_DATA_TABLE	Represents a transaction data table. It stores the status of completed transactions and is used for queries in scenarios such as minor compactions and FAST COMMIT.
MDS_DATA_ID	Memory ID of multi-source data
LIBEASY	Indicates the memory of the network framework (EASY).
LOGGER_CTX_ID	Represents the program log memory context ID.
RPC_CTX_ID	Represents the RPC framework memory context ID.
PKT_NIO	Represents the memory of the network framework (pkt_nio).
SCHEMA_SERVICE	Represents the memory for schema metadata, such as tables and databases.

Mapping between CTX_NAME and MOD_NAME

The common correspondence between CTX_NAME and MOD_NAME is as follows:

CTX_NAME	MOD_NAME	TENANT
DEFAULT_CTX_ID	MysqlRequesReco: MySQL request record module. LogAggreBuffer: log aggregation buffer module. PartitLogServic: partition log service module. SqlDtl: SQL details module. TransAudit: transaction audit module. IoControl: Input/Output control module. ResultSet: the collection module for query results.	ALL
DEFAULT_CTX_ID	SchemaSysCache: a system-level cache module for caching schema information. SeArray: a sortable array module. SstaMicrBlocAll: statistics, microblocks, and other modules CsSstableReader: a reader for compressed tables. TmpBlockManager: temporary block manager. TenantSchemMgr: tenant schema manager. DecoderCtx: the decoder context. SqlSqcHandler: SQL semantic processor.	500
SQL_EXEC_CTX_ID	CostBasedRewrit: cost-based rewrite optimizer. SqlExecutor: SQL executor. SqlPsCache: SQL parameter cache module. OB_SQL_AGGR_FUNC_ROW: row object of the SQL aggregate function.	ALL
WORK_AREA	SqlAggrFuncRow: row object of SQL aggregate functions. WindowAggProc: window aggregation processing module. SqLWindoRowStor: the module for storing window row information. SqLChunkRowStor: storage block row-related module SqLTempTabLeRow: temporary table row-related module ConnectByPump: the data transfer module for connection operations. SqlSortRow: the row sorting module. SortOpRows: the collection of row objects to be sorted. SqLHashDisRowSt: Hash distributed row storage module SqLHashDist: hash distribution module. HashNodeGrouRow: Hash node grouping row-related module HashDistinctOp: Hash deduplication operation module. ArenaHashJoin: the memory space management module for hash join operations. HtOpAlloc: Hash table operation allocation module.
PLAN_CACHE_CTX_ID	OB_SQL PHY_PLAN: the query plan module. OB_SQL_PLAN_CACHE: query plan cache module OB_SQL_PHY_PL_OBJ: Query plan object module PRE_CALC_EXPR: Precomputed expressions module.
TRANS_CTX_MGR_ID	PartTranCtxMgr: partition transaction context. TenantCtxAlloca: Allocate context for the tenant.
TX_CALLBACK_CTX_ID	MemtableCallbac: the module related to memory table callback.
REPLAY_STATUS_CTX_ID	ReplayStatus: the module related to the replay status.
CO_STACK	CO_STACK: Coroutine stack-related modules	500
STORAGE_LONG_TERM_META_CTX_ID	Partition: the partition object. PartitioStore: partition storage module. PartitioStorage: partition storage.
STORAGE_SHORT_TERM_META_CTX_ID	Sstable: SSTable SstableMeta: Meta tenant SSTable table MemtableObject: the in-memory table object.
ALL	OB_COMMON_ARRAY: OceanBase common array	ALL

Impact of common SQL operations on memory CTX

In OceanBase Database, each SQL execution or operation corresponds to a specific CTX. Due to differences in data volume and operation complexity, the memory used by the CTX may lead to increased memory consumption. The following are some common SQL executions or operations that may cause the usage of memory by certain CTXs to increase:

Sorting large volumes of data (ORDER BY, GROUP BY, etc.): Sorting operations require loading data into memory for processing, which may lead to increased memory usage in the PLAN_CACHE_CTX_ID, MEMSTORE_CTX_ID, and DEFAULT_CTX_ID contexts.
Aggregation of large data volumes (SUM, AVG, MAX, MIN, etc.): Aggregation operations require loading data into memory for computation, which may lead to increased memory usage in PLAN_CACHE_CTX_ID, MEMSTORE_CTX_ID, and DEFAULT_CTX_ID.
Connections (JOINs) with large data volumes: The join operation requires loading data into memory for matching, which may lead to increased memory usage in the PLAN_CACHE_CTX_ID, MEMSTORE_CTX_ID, and DEFAULT_CTX_ID contexts.
Queries with large data volumes (SELECT): The query operation needs to load data into memory for filtering and sorting, which may lead to increased memory usage in the PLAN_CACHE_CTX_ID, MEMSTORE_CTX_ID, and DEFAULT_CTX_ID contexts.
Writing large volumes of data (INSERT, UPDATE, DELETE, etc.): Write operations require transaction management and processing, which may lead to increased memory usage in TRANS_CTX_MGR_ID, MEMSTORE_CTX_ID, and DEFAULT_CTX_ID.
Logs with large data volumes (such as REDO, UNDO, and BINLOG logs): Log operations require loading data into memory for processing, which may lead to increased memory usage in the TRANS_CTX_MGR_ID, DEFAULT_CTX_ID, LOB_CTX_ID, and TX_DATA_TABLE variables.

Sample query

The user tenant queries the memory statistics of the current node for the current tenant, displaying the first 10 records.

obclient [SYS]> SELECT * FROM SYS.V$OB_MEMORY WHERE ROWNUM <= 10;

The query result is as follows:

+-----------+----------------+----------+-------------------------------+-----------------+-------+-----------+-----------+
| TENANT_ID | SVR_IP         | SVR_PORT | CTX_NAME                      | MOD_NAME        | COUNT | HOLD      | USED      |
+-----------+----------------+----------+-------------------------------+-----------------+--------+-----------+-----------+
|      1004 | 172.xx.xxx.xxx |     2882 | CO_STACK                      | CoStack         |    198 | 102187008 | 101996928 |
|      1004 | 172.xx.xxx.xxx |     2882 | CO_STACK                      | KvstorCacheMb   |      0 |         0 |         0 |
|      1004 | 172.xx.xxx.xxx |     2882 | DEFAULT_CTX_ID                | ApplySrv        |      1 |    409600 |    401408 |
|      1004 | 172.xx.xxx.xxx |     2882 | DEFAULT_CTX_ID                | APPLY_STATUS    |      1 |      8128 |      7936 |
|      1004 | 172.xx.xxx.xxx |     2882 | DEFAULT_CTX_ID                | ArcFetchQueue   |      1 |   8540160 |   8519680 |
|      1004 | 172.xx.xxx.xxx |     2882 | DEFAULT_CTX_ID                | ArcSenderQueue  |      1 |    933888 |    931072 |
|      1004 | 172.xx.xxx.xxx |     2882 | DEFAULT_CTX_ID                | AsyncFreezeTabl |      1 |    114688 |    111096 |
|      1004 | 172.xx.xxx.xxx |     2882 | DEFAULT_CTX_ID                | Autoincrement   |      1 |     40960 |     37032 |
|      1004 | 172.xx.xxx.xxx |     2882 | DEFAULT_CTX_ID                | Backup          |      1 |     16384 |     12344 |
|      1004 | 172.xx.xxx.xxx |     2882 | DEFAULT_CTX_ID                | BackupIOPerMgr  |      1 |      1152 |       960 |
+-----------+----------------+----------+-------------------------------+-----------------+--------+-----------+-----------+
10 rows in set

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