9.138 V$XSTREAM_APPLY_READER

V$XSTREAM_APPLY_READER displays information about each XStream apply reader. The apply reader is a process which reads (dequeues) messages from the queue, computes message dependencies, and builds transactions. It passes the transactions on to the coordinator in commit order for assignment to the apply servers. An apply reader is a subcomponent of an apply process, outbound server, or inbound server.
Column Datatype Description

SID

NUMBER

Session ID of the reader's session

SERIAL#

NUMBER

Serial number of the reader's session

APPLY#

NUMBER

Apply process number. An apply process is an Oracle background process, prefixed by ap.

APPLY_NAME

VARCHAR2(128)

Name of the apply process

STATE

VARCHAR2(36)

Shows the state of the apply reader and the hash server. The possible values include:

  • INITIALIZING - Starting up

  • IDLE - Performing no work

  • DEQUEUE MESSAGES - Dequeuing messages from the queue

  • SCHEDULE MESSAGES - Computing dependencies between messages and assembling messages into transactions

  • SPILLING - Spilling unapplied messages from memory to hard disk

  • PAUSED - WAITING FOR DDL TO COMPLETE - Waiting for a data definition language (DDL) logical change record (LCR) to be applied

The state of the apply reader is displayed first, followed by the state of the hash server. A semicolon separates the apply reader state from the hash server state.

TOTAL_MESSAGES_DEQUEUED

NUMBER

Total number of messages dequeued since the apply process was last started

TOTAL_MESSAGES_SPILLED

NUMBER

Number of messages spilled by the reader since the apply process was last started

DEQUEUE_TIME

DATE

Time when the last message was received

DEQUEUED_MESSAGE_NUMBER

NUMBER

Number of the last message received

DEQUEUED_MESSAGE_CREATE_TIME

DATE

For captured messages, creation time at the source database of the last message received. For user-enqueued messages, time when the message was enqueued into the queue at the local database.

SGA_USED

NUMBER

Amount (in bytes) of SGA memory used by the apply process since it was last started

ELAPSED_DEQUEUE_TIME

NUMBER

Time elapsed (in hundredths of a second) dequeuing messages since the apply process was last started

ELAPSED_SCHEDULE_TIME

NUMBER

Time elapsed (in hundredths of a second) scheduling messages since the apply process was last started. Scheduling includes computing dependencies between messages and assembling messages into transactions.

ELAPSED_SPILL_TIME

NUMBER

Elapsed time (in hundredths of a second) spent spilling messages since the apply process was last started

OLDEST_SCN_NUM

NUMBER

Oldest SCN

OLDEST_XIDUSN

NUMBER

Transaction ID undo segment number of the oldest transaction that either has been applied or is being applied

OLDEST_XIDSLT

NUMBER

Transaction ID slot number of the oldest transaction that either has been applied or is being applied

OLDEST_XIDSQN

NUMBER

Transaction ID sequence number of the oldest transaction that either has been applied or is being applied

SPILL_LWM_SCN

NUMBER

Spill low-watermark SCN

PROXY_SID

NUMBER

When the apply process uses combined capture and apply, the session ID of the propagation receiver that is responsible for direct communication between capture and apply. If the apply process does not use combined capture and apply, then this column is 0.

PROXY_SERIAL

NUMBER

When the apply process uses combined capture and apply, the serial number of the propagation receiver that is responsible for direct communication between capture and apply. If the apply process does not use combined capture and apply, then this column is 0.

PROXY_SPID

VARCHAR2(12)

When the apply process uses combined capture and apply, the process identification number of the propagation receiver that is responsible for direct communication between capture and apply. If the apply process does not use combined capture and apply, then this column is 0.

BYTES_RECEIVED

NUMBER

When the apply process uses combined capture and apply, the number of bytes received by the apply process from the capture process since the apply process last started. If the apply process does not use combined capture and apply, then this column is not populated.

DEQUEUED_POSITION

RAW(64)

Dequeued position. This column is populated only for an apply process that is functioning as an XStream inbound server.

SPILL_LWM_POSITION

RAW(64)

Spill low-watermark position. This column is populated only for an apply process that is functioning as an XStream inbound server.

OLDEST_TRANSACTION_ID

VARCHAR2(128)

Oldest transaction ID

TOTAL_LCRS_WITH_DEP

NUMBER

Total number of LCRs with row-level dependencies since the apply process last started

TOTAL_LCRS_WITH_WMDEP

NUMBER

Total number of LCRs with watermark dependencies since the apply process last started.

A watermark dependency occurs when an apply process must wait until the apply process's low watermark reaches a particular threshold.

TOTAL_IN_MEMORY_LCRS

NUMBER

Total number of LCRs currently in memory

SGA_ALLOCATED

NUMBER

The total amount of shared memory (in bytes) allocated from the XStreams pool for the apply process since the apply process last started

CON_ID

NUMBER

The ID of the container to which the data pertains. Possible values include:

  • 0: This value is used for rows containing data that pertain to the entire CDB. This value is also used for rows in non-CDBs.

  • 1: This value is used for rows containing data that pertain to only the root

  • n: Where n is the applicable container ID for the rows containing data

Note:

The ELAPSED_SCHEDULE_TIME column is only populated if the TIMED_STATISTICS initialization parameter is set to true, or if the STATISTICS_LEVEL initialization parameter is set to TYPICAL or ALL.