Scott Marlowe wrote:
On Sat, Jan 31, 2009 at 2:13 AM, Erik Jones <ejones@xxxxxxxxxxxxxx> wrote:
On Jan 30, 2009, at 11:37 AM, durumdara wrote:
- I can add/modify a table, or a field to a table without "full lock" on
the table (like DBISAM restructure). Like in FireBird, where the "add field"
change only the table description. I don't know that PG supports this way of
the DB modifying.
Nope. PostgreSQL is an all or nothing transactional database. I'd never
heard of DBISAM before you mentioned it and have never used Firebird. After
doing a little reading it turns out that if you plan to use transactions at
all (which is very likely given even just the little you've described about
the applications you're building) then you should realize that altering
tables is not compatible with transactions and doing so will automatically
commit any open transactions on the table.
Are talking about pgsql or some other database? Everything in pgsql
can be done in a transaction, except create / drop database /
tablespace.
Looking into Firebird I couldn't
find how it handles (or doesn't) that at all I but I did see that it will
happily let you add a new not null column with no default to a table by
writing nulls for the new attribute for any existing columns. That already
makes me queasy.
That's pretty much what pgsql does. Why does it make you queasy?
I think the key is that the new column is NOT NULL, so defaulting the
new column's values to NULL results in immediate data integrity
inconsistency.
If I remember rightly, PG doesn't allow this: you have to create the
column as NULL, UPDATE and then add the NOT NULL constraint, or perhaps
(I haven't tried this) create the column with a default and then remove
it immediately afterwards.
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