On 01/09/2014 08:51 AM, Day, David wrote:
I have needs to do selective schema or table restorations and the pg_restore
utility seems to have hooks for this, yet seems deficient for this type
of problem.
It appears that I have to develop a custom script to do what I think would
be a standard kind of restorations.
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Given: Postgres 9.3 and I have dumped my database via:
pg_dump –Fc –U <superuser> my_db –f archive_file
I have no problem doing a total restoration
e.g.
pg_restore –c –U <supeuser> -d my_db archive_file
Assuming I have not had a catastrophic error but merely wish to address
schemas
or tables used for decision making that have been altered by users into
sub-optimal
condition, then if I attempt to do selective restorations of a schema
or tables in the database:
( e.g. pg_restore –c -n <some_schema> -U <superuser> -d my_db
archive_file )
I encounter restoration problems over dependencies with suggestions/Hints:
“ HINT: Use DROP ... CASCADE to drop the dependent objects too.”
Well for what it is worth, that is documented.
http://www.postgresql.org/docs/9.3/interactive/app-pgdump.html
"Note: When -n is specified, pg_dump makes no attempt to dump any other
database objects that the selected schema(s) might depend upon.
Therefore, there is no guarantee that the results of a specific-schema
dump can be successfully restored by themselves into a clean database."
So it appears that I now have to develop a custom script to do what I
think would
be a standard kind of restoration.
Well I think that is the issue that it is not really standard or at
least easy. The possible combinations of schemas, dependencies across
schemas, ownership across objects makes this complicated to do on a
selective basis. Furthermore when you are using -n using are asking for
a specific schema, it sort of breaks the contract to drag in objects
from other schemas.
I would think that there ought to be an some additional options to
pg_restore.
i.e an option that turns a DROP into a DROP with CASCADE and or
DISABLES constraint checking while the schema/table is being restored.
So you want to start dropping objects outside the schema you are
restoring, seems like a foot gun to me.
In addition I would think that with “-a” , data only option, there ought
to be an assistive option that allows for the table to
truncated/cleaned so that
Probably because it is relatively easy to roll your own solution to this.
the generated COPY commands do not append to the table resulting in
PRIMARY KEY violations.
In any event I have not found a straight forward way of using pg_restore
to do selective restorations or have found some ways of doing certain
tables but had to remove Foreign Keys to make it work which seems like a
poor bargain. I think I know how to customize the output to do the task,
it just seems that pg_restore should be
able to do this without my additional efforts.
In the foreseeable future that is how you will need to handle it. Where
the choice is either roll your own script or use one of the existing
migration solutions, e.g Alembic, Sqitch, etc
I am hopeful that there might be some instructive thoughts on selective
restorations that have not occurred to me.
( options that I have played with: -n –t –section=data –a –c
–disable-triggers -1 )
Regards
Dave Day
--
Adrian Klaver
adrian.klaver@xxxxxxxxx
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