Fixes #4832: Add migration script to changed id type from integer to

[VinceMacBuche]

bigint

http://www.rudder-project.org/redmine/issues/4832

[jooooooon]

Are you sure abuot this space?

And can you please always refer to variables in bash using the ${x} syntax, not just $x?
(same question and request below)

[ncharles]

I'm not a big fan of this; every time we needed to detect something we relied on counting; could we do the same ?
RES=$(su - postgres -c "psql -t -d rudder -c "select count(*) from information_schema.columns where table_name='ruddersysevents' and column_name='id' and data_type='integer'")

[VinceMacBuche]

Sure about the space, the result is ''' integer''' don't knwo where i got that damn space though ...)

Adding the curly braces, i was sure i added them ...

[VinceMacBuche]

That seems a good idea, thanks Nico !!

[VinceMacBuche]

Thanks Nico and Jon, I made corrections on the PR (now compare with a integer, not a string anymore, fixes version numbers and add curly braces)

[jooooooon]

OK, this code now looks fine.

However, I am a little concerned about what we're doing here: modifying the DB schema is not an anodine operation, should this really be happening in a patch release on a stable branch? What motivates this?

Also, if we need a BigInt, I'm assuming this will affect users that have a LOT of data. How long does this type change take?

[VinceMacBuche]

hmm... the convertion is almost instant on postgres 9.1+ but can be very long on older versions : http://blog.endpoint.com/2012/11/postgres-alter-column-problems-and.html

[VinceMacBuche]

on postgres 9.1 we can use that command ...

on older ... alter table lock the database and rewrite the whole table, which can be very long. There is another way to do this, but it's quite dangerous ..

It needs to modify directly the type in postgres internal databases (table pg_attribute) instead of using postgres basic command ...

[VinceMacBuche]

Ok, i misread ... it will always be long to use 'alter table ... set type bigint' since it has to rewite table ... It's only on certian type (varchar to text )... However i cant find the whole text explaining this ...

[VinceMacBuche]

faster ways are :

• dump the table, truncate it, modify the column, import datas
• crete a colmumn '''newid''' of type bigint, copy all datas from '''id''' to '''newid''' , drop '''id', rename '''newid''' to '''id'''

[VinceMacBuche]

Jon, we found another way to do it:

We decided to do:
In a transaction:
Rename table to old_table
drop all indexes
create new "table" with bigint
Create new indexes
End of transaction
Copy all lines of "old_table" int "table"
Drop "old_table"

That process can still be long (insertion of million of lines can take some times), but this will not block the database ...

But still the question is a stake if we need to do this in 2.6 or 2.11 ...

I think this is quite important, since we can't force people with big installation to not use a stable version ...

[VinceMacBuche]

Closing that pull request, becasue of two things:

First: we decided to move it in 2.10
Secondly: We decided to not provide a migration script that will automatically do the migration, but a script that should run manually due to the huge impact. In the migration script we should only add a Warning to alert eh user oon the need