Note
This view was renamed from GV$MEMORY to GV$OB_MEMORY starting with V4.0.0.
Purpose
This view displays the memory statistics of all nodes for the current tenant.
Columns
| Column | Type | Nullable? | Description |
|---|---|---|---|
| TENANT_ID | bigint(20) | NO | The tenant ID. |
| SVR_IP | varchar(46) | NO | The IP address of the server. |
| SVR_PORT | bigint(20) | NO | The port number of the server. |
| CTX_NAME | varchar(256) | NO | The name of the CTX to which the memory belongs. |
| MOD_NAME | varchar(256) | NO | The name of the Mod to which the memory belongs. |
| COUNT | decimal(20,0) | NO | The difference between the allocated memory and the released memory, that is, the number of memory units currently used by the Mod. |
| HOLD | decimal(20,0) | NO | The size of memory currently occupied by the Mod. |
| USED | decimal(20,0) | NO | The size of memory currently used by the Mod, in bytes. |
CTX_NAME values
The following table describes the names and meanings of common memory CTXs.
| CTX_NAME | Description |
|---|---|
| DEFAULT_CTX_ID | The ID of the unpartitioned memory set context. |
| MEMSTORE_CTX_ID | The ID of the user MemTable data context. |
| TRANS_CTX_MGR_ID | The ID of the transaction context. |
| PLAN_CACHE_CTX_ID | The ID of the execution plan cache context. |
| GLIBC | The memory allocated by using the Glibc Malloc interface. |
| CO_STACK | The memory of the thread execution stack. |
| KVSTORE_CACHE_ID | The ID of the dynamically scalable cache. |
| META_OBJ_CTX_ID | The memory of the stored metadata, such as macroblock meta data. |
| TX_CALLBACK_CTX_ID | The ID of the transaction callback context. This context is used to record some modifications during transaction execution. When a transaction is committed or rolled back, the corresponding data can be found and operated on. |
| LOB_CTX_ID | The Allocator ID in the ObLobManager. |
| PS_CACHE_CTX_ID | The cache ID of the PREPARE stmt_name FROM preparable_stmt statement. |
| TX_DATA_TABLE | The transaction data table. It stores the status of resolved transactions and is used for dumping queries in scenarios such as uncommitted transactions and FAST COMMIT. |
| MDS_DATA_ID | The memory ID of multi-source data |
| LIBEASY | The memory of the network framework (EASY). |
| LOGGER_CTX_ID | The ID of the program log memory context. |
| RPC_CTX_ID | The ID of the RPC framework memory context. |
| PKT_NIO | The memory of the network framework (pkt_nio). |
| SCHEMA_SERVICE | The memory of the schema metadata, such as tables and databases. |
Correspondence between CTX_NAME and MOD_NAME
Common CTX_NAME and MOD_NAME correspondences are as follows:
| CTX_NAME | MOD_NAME | TENANT |
|---|---|---|
| DEFAULT_CTX_ID |
|
ALL |
|
500 | |
| SQL_EXEC_CTX_ID |
|
ALL |
| WORK_AREA |
|
|
| PLAN_CACHE_CTX_ID |
|
|
| TRANS_CTX_MGR_ID |
|
|
| TX_CALLBACK_CTX_ID | MemtableCallbac: module related to memory table callbacks | |
| REPLAY_STATUS_CTX_ID | ReplayStatus: module related to replay status | |
| CO_STACK | CO_STACK: coroutine stack module | 500 |
| STORAGE_LONG_TERM_META_CTX_ID |
|
|
| STORAGE_SHORT_TERM_META_CTX_ID |
|
|
| 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. The size of the data and the complexity of the operation can lead to an increase in memory usage for the CTX. The following are some common SQL operations that may cause an increase in memory usage for certain CTXs:
Sorting large amounts of data (ORDER BY, GROUP BY, etc.): Sorting operations require loading data into memory for sorting, which may lead to an increase in memory usage for the PLAN_CACHE_CTX_ID, MEMSTORE_CTX_ID, and DEFAULT_CTX_ID CTXs.
Aggregating large amounts of data (SUM, AVG, MAX, MIN, etc.): Aggregation operations require loading data into memory for calculation, which may lead to an increase in memory usage for the PLAN_CACHE_CTX_ID, MEMSTORE_CTX_ID, and DEFAULT_CTX_ID CTXs.
Joining large amounts of data (JOIN): Join operations require loading data into memory for matching, which may lead to an increase in memory usage for the PLAN_CACHE_CTX_ID, MEMSTORE_CTX_ID, and DEFAULT_CTX_ID CTXs.
Querying large amounts of data (SELECT): Query operations require loading data into memory for filtering and sorting, which may lead to an increase in memory usage for the PLAN_CACHE_CTX_ID, MEMSTORE_CTX_ID, and DEFAULT_CTX_ID CTXs.
Writing large amounts of data (INSERT, UPDATE, DELETE, etc.): Writing operations require managing and processing transactions, which may lead to an increase in memory usage for the TRANS_CTX_MGR_ID, MEMSTORE_CTX_ID, and DEFAULT_CTX_ID CTXs.
Logging large amounts of data (REDO, UNDO, BINLOG, etc.): Logging operations require loading data into memory for operations, which may lead to an increase in memory usage for the TRANS_CTX_MGR_ID, DEFAULT_CTX_ID, LOB_CTX_ID, and TX_DATA_TABLE CTXs.