FK from logged to unlogged table?
Hello,
I'm looking to improve bulk write performance on a table of about 23 million rows by setting it unlogged. If lost, the table can be re-generated from archived raw data. The unlogged table would be referenced from a different, logged, table by a sparse but very important foreign key.
If the unlogged table is lost, I can repair the foreign key data by re-uploading the raw data and following a different unique key. However, this would be annoying and I would rather not have to implement it if I can protect the keyed records instead.
1. Is it allowed to key from a logged table to an unlogged table?
2. What is the system behavior if the unlogged table is lost?
3. Is there a clean way to protect only the subset of records that are keyed? (Yes, I am considering periodic backups to an archive table, but there would still be some repair needed that way).
Thanks! Nice to meet you all.
-Dolan
On Friday, November 21, 2025, <dolan@directdemocracysolutions.com> wrote:
Hello,
I'm looking to improve bulk write performance on a table of about 23
million rows by setting it unlogged. If lost, the table can be re-generated
from archived raw data. The unlogged table would be referenced from a
different, logged, table by a sparse but very important foreign key.If the unlogged table is lost, I can repair the foreign key data by
re-uploading the raw data and following a different unique key. However,
this would be annoying and I would rather not have to implement it if I can
protect the keyed records instead.1. Is it allowed to key from a logged table to an unlogged table?
2. What is the system behavior if the unlogged table is lost?
3. Is there a clean way to protect only the subset of records that are
keyed? (Yes, I am considering periodic backups to an archive table, but
there would still be some repair needed that way).
Both 1 and 2 Feels like something you should take the couple of minutes to
try. For 3, it’s an unlogged table - the entire thing.
David J.
<dolan@directdemocracysolutions.com> wrote:
Is it allowed to key from a logged table to an unlogged table?
I tried and it seems not:
create unlogged table u(i int primary key);
create table l(i int references u);
ERROR: constraints on permanent tables may reference only permanent tables
Interestingly it works in the other direction. I assume it's forbidden
because the loss of the unlogged table will break the constraint. I
expect you could simulate the foreign key with a trigger, but I'm not
sure you should.
Is there a clean way to protect only the subset of records that are keyed?
I wonder if partitioning could help you. I believe it's possible to
have logged and unlogged partitions in the same table [1]/messages/by-id/ZiiyGFTBNkqcMQi_@paquier.xyz.
I'm sure you've explored other options for faster inserts [2]https://www.postgresql.org/docs/current/populate.html. Most
of the times I've wanted to use an unlogged table, I've decided it's
not worth the rescue effort.
Thanks,
Bernice
[1]: /messages/by-id/ZiiyGFTBNkqcMQi_@paquier.xyz
[2]: https://www.postgresql.org/docs/current/populate.html