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With the current release, you have to do an unload/reload as you say.
No, Ingres does not have a snapshot file. They have three types of locks...
Shared, exclusive, and no-locks. Unless you use no-locks, (where you have
to deal with the locking yourself in the application), the readers and the
writers will interfere with each other, which can lead to concurrency
problems. Since RDB has a snapshot file, shared read transactions won't
interfere with the writers. (assuming that you haven't disabled snaps!).
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I've just read Michael Booths ' Ingres - Competitive Fact Sheet ' and
there is no mention of the lack of snapshotting/multiversioning
capability within the Ingres database ...... I've got an inconsistent
read here !
Metadata mods - as I have not got access to an Ingres system I am
unable to test this out. If they cannot do it without an unload/reload
then there sales sheet ( page 23 of the Ingres overview document,
section entitled 'Elect a new administration, 3rd bullet) is
seriously misleading and what there salesman told me is seriously
misleading.
So what gives ? Are they telling porkies ?
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| Lack of multiversioning is not in the fact sheet because it was too
technical to explain, and space was at a premium as that document had
to be kept to three pages. As far as I know, the lack of snapshotting
is real, as is the NOLOCK problem. That is, using the NOLOCK type of
lock for reads allows updates to occur to the data with no protection
for the reader. In other words, terribly inconsistent data. And this
has been verified by the person we recently hired from Ingres.
---- Michael Booth
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| Further....
- Until Ingres comes out with their ALTER TABLE feature (non-ANSI
standard at this point), they *DO NEED* to unload/reload their tables
when they want to modify it (e.g. change or add a data field). I know
that they are planning to add this in the future; until then it is a
knock-off.
- Tables need to be locked (taken off-line) to create indexes.
- WHen they say "Dynamic modification of databases etc. without
processing interruption" could mean dynamic modification of the data
(which is true); this is not what we are talking about above.
- Ingres may sometimes refer to their Checkpoint feature as "taking
snapshots of the database". All they mean here is that they are taking
a static copy of the database. It *IS NOT* the same type of
functionality that Rdb supports. Therefore, Ingres does not provide
Snapshot capabilties as we define it with Rdb.
--Lourdes Roberts
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