On 2020/10/01 12:04, osumi.takami...@fujitsu.com wrote:
Hello.
Can they use a database with all unlogged tables?
Unfortunately, no. They want to switch a cluster condition to "without WAL
logging"
only when they execute night bulk loading for their data warehouse.
In other words, they would like to keep their other usual operations with WAL.
In addition, using all tables as unlogged brings about the risk to
lose data warehouse's data caused by an unexpected server crash or power
outage.
But the same issue can happen even in the proposed approach because
Tsunakawa-san explains as follows?
Sorry, my last expression about "to lose data" was not precise.
When unlogged tables are used and the server is crashed unexpectedly,
all data after the last backup is truncated without WAL, right ?
In this case, sequential commands for unlogged tables disappear.
To avoid this issue we can mark the table as logged. You may be worried about
that ALTER TABLE SET LOGGED/UNLOGGED would take a long time because
the table needs to be rewriitten. One idea for that is to improve that command
so that it skips the table rewrite if wal_level=minimal.
Of course, also you can change wal_level after marking the table as unlogged.
Regards,
--
Fujii Masao
Advanced Computing Technology Center
Research and Development Headquarters
NTT DATA CORPORATION
