Обсуждение: RE: [HACKERS] Transaction logging

Your getting me excited about 6.5.  Is there a projected release date for
6.5?  Is there any information on transaction logging?  Is there anything I
can do to help?  I am curious about these items because they will make my
life much easier in the upcoming months as I migrate my application to
Postgres.  Working around these could be very difficulty or near impossible.
-----Original Message-----From:    Bruce Momjian [SMTP:maillist@candle.pha.pa.us]Sent:    Tuesday, February 23, 1999
8:02PMTo:    Michael DavisCc:    pgsql-general@postgreSQL.org; pgsql-hackers@postgreSQL.orgSubject:    Re: [GENERAL]
Transactionlogging
 
> What would it take to have transaction logging added to Postgres.
I am a> c/c++ programmer and will consider contributing to the Postgres
development> effort.  I really like everything I see and read about Postgres.
As a> result, I am strongly considering Postgres as the database engine
for my> Membership database application.  My customer is willing to invest
in a> commercial database, but most of the commercial databases I have
briefly> looked at fall a little short in one way or another.  I have
several> concerns/needs that I am willing to implement and/or support:> >     - Outer join support in views
In the works.  Perhaps for 6.5, probably not.
> >     - Transaction logging> >     - Some form of mirroring, shadowing, or replication> >     - The current locking
mechanismis of some concern.  I need
 
to make> sure that one user can read a record and then a second can read
and update> that same record.
MVCC locking in 6.5.  Will do what you need.> >     - If the first user attempts to update that record, what
happens?
Hard to explain.  Will wait or update a copy while read's use an
oldercopy fo the row.

--   Bruce Momjian                        |  http://www.op.net/~candle  maillist@candle.pha.pa.us            |  (610)
853-3000 +  If your life is a hard drive,     |  830 Blythe Avenue  +  Christ can be your backup.        |  Drexel
Hill,Pennsylvania
 
19026

> Your getting me excited about 6.5.  Is there a projected release date for
> 6.5?  Is there any information on transaction logging?  Is there anything I
> can do to help?  I am curious about these items because they will make my
> life much easier in the upcoming months as I migrate my application to
> Postgres.  Working around these could be very difficulty or near impossible.

We are waiting for the MVCC/locking stuff to be finished.  Everything
else is mostly ready.  We were planning for Feb 1, but we must wait.

--  Bruce Momjian                        |  http://www.op.net/~candle maillist@candle.pha.pa.us            |  (610)
853-3000+  If your life is a hard drive,     |  830 Blythe Avenue +  Christ can be your backup.        |  Drexel Hill,
Pennsylvania19026
 

>
> Your getting me excited about 6.5.  Is there a projected release date for
> 6.5?  Is there any information on transaction logging?  Is there anything I
> can do to help?  I am curious about these items because they will make my
> life much easier in the upcoming months as I migrate my application to
> Postgres.  Working around these could be very difficulty or near impossible.

    I've  spent  some  time  thinking  about transaction log. The
    first idea was to log queries and in some way. But I  had  to
    drop  that  approach  because  there are functions (and users
    could have written threir own ones too),  that  don't  return
    the  same result when the database later get's rolled forward
    (e.g.  anything  handling   date's/times).    And   OTOH   an
    application  could  SELECT  something  from the database that
    maybe got created by a sequence, and uses this value then  in
    another  INSERT.   But when recovering the database, it isn't
    guaranteed that all the data  will  get  the  same  sequences
    again (race conditions in concurrent queries). How should the
    transaction log now know that this one constant value in  the
    query   must  be  substituted  by  another  value  to  ensure
    referential integrity? Absolutely impossible.

    So the only way I see is to use some sort  of  image  logging
    from  inside  the  heap  access  methods.  Would be much more
    tricky to dump and recover.


Jan

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