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V$ARCHIVE_DEST(TRANSMIT_MODE) SYNCHRONOUS vs PARALLELSYNC vs ASYNCHRONOUS + 2 questions

DBA AbhishekDec 13 2016 — edited Dec 13 2016

Hi,

I have 3 questions.


1)

I am trying the understand the difference between SYNCHRONOUS vs PARALLELSYNC vs ASYNCHRONOUS redo transmit modes.

From the documentation, I only find definitions for SYNCHRONOUS and ASYNCHRONOUS transmit modes

Synchronous

The synchronous redo transport mode transmits redo data synchronously with respect to transaction commitment. A transaction cannot commit until all redo generated by that transaction has been successfully sent to every enabled redo transport destination that uses the synchronous redo transport mode.

Asynchronous

The asynchronous redo transport mode transmits redo data asynchronously with respect to transaction commitment. A transaction can commit without waiting for the redo generated by that transaction to be successfully sent to any redo transport destination that uses the asynchronous redo transport mode.

But I do not understand what PARALLELSYNC is. Can someone please help me understand this mode?

2)

Moreover, If I DO NOT have standby redologs/ no realtime apply, can the transmit mode still be SYNC? I ask because I see it in v$archive_dest after setting this

SQL> alter system set log_archive_dest_3='SERVICE=OT0925C.xxxx.com ARCH ASYNC NOAFFIRM VALID_FOR=(ONLINE_LOGFILES,PRIMARY_ROLE) DB_UNIQUE_NAME=OT0925C';

System altered.

SQL> select process,transmit_mode,affirm from v$archive_dest where dest_id in (1,2,3);

PROCESS    TRANSMIT_MOD AFF

---------- ------------ ---

ARCH       SYNCHRONOUS  NO

LGWR       PARALLELSYNC YES

ARCH       SYNCHRONOUS  NO

3)

What's the difference in having ARCH vs LGWR for redo transport? I do not understand.

Thanks!

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