RE: Implement UNLOGGED clause for COPY FROM

Hello,


I think it's worth thinking about a sophisticated feature like Oracle's UNRECOVERABLE data loading (because SQL
Server'sBCP load utility also has such a feature, but for an empty table), how about an easier approach like MySQL?  I
expectthis won't complicate Postgres code much.
 

The customer is using Oracle RAC for high availability of a data warehouse.  Then, I think they can use the traditional
shareddisk-based HA clustering, not the streaming replication when they migrate to Postgres.
 

They load data into the data warehouse with the nightly ETL or ELT.  The loading window is limited, so they run
multipleconcurrent loading sessions, with the transaction logging off.  They probably use all resources for the data
loadingduring that period.
 

Then, you might think "How about turning fsync and full_page_writes to off?"  But the customer doesn't like to be
worriedabout the massive amount of WAL generated during the loading.
 


OTOH, the latest MySQL 8.0.21 introduced the following feature.  This is for the initial data loading into a new
databaseinstance, though.
 


https://dev.mysql.com/doc/refman/8.0/en/innodb-redo-log.html#innodb-disable-redo-logging
--------------------------------------------------
Disabling Redo Logging
As of MySQL 8.0.21, you can disable redo logging using the ALTER INSTANCE DISABLE INNODB REDO_LOG statement. This
functionalityis intended for loading data into a new MySQL instance. Disabling redo logging speeds up data loading by
avoidingredo log writes and doublewrite buffering.
 

Warning
This feature is intended only for loading data into a new MySQL instance. Do not disable redo logging on a production
system.It is permitted to shutdown and restart the server while redo logging is disabled, but an unexpected server
stoppagewhile redo logging is disabled can cause data loss and instance corruption.
 

Attempting to restart the server after an unexpected server stoppage while redo logging is disabled is refused with the
followingerror:
 

[ERROR] [MY-013578] [InnoDB] Server was killed when Innodb Redo 
logging was disabled. Data files could be corrupt. You can try 
to restart the database with innodb_force_recovery=6
In this case, initialize a new MySQL instance and start the data loading procedure again.
--------------------------------------------------


Following this idea, what do you think about adding a new value "none" to wal_level, where no WAL is generated?  The
settingof wal_level is recorded in pg_control.  The startup process can see the value and reject recovery after
abnormalshutdown, emitting a message similar to MySQL's.
 

Just a quick idea.  I hope no devil will appear in the details.


Regards
Takayuki Tsunakawa