Horton

Thread

  1. MVCC works in serialized mode!

    Vadim Mikheev <vadim@krs.ru> — 1998-12-16T13:00:54Z

    CVS is just updated...

Please try concurrent writes/reads...

It'll take some time to implement READ COMMITTED mode...

Note:

1. Vacuum is not updated yet and so will remove deleted tuples
   though some xactions would like to see them in selects...

2. LOCK TABLE modes are not yet implemented...

3. As well as SELECT ... FOR UPDATE: I need in advice here!

   Do Oracle, Informix etc support SELECT FOR UPDATE if
   there are aggregates, group by, distinct in SELECT ???
   Is SELECT FOR UPDATE allowed in subqueries ???

4. Rtree & gist indices use _relation level_ locking -
   no wish, no time to change them...
   Executor locks them in exclusive mode (on relation level)
   for update/insert and so prevents deadlocks...
   These locks released after _query_ is done - not so bad
   for concurrency...

5. Hash & btree indices use _page level_ locking and so
   are "opened" for deadlocks -:))
   (In the case of concurrent inserts/updates when
    indices are used for scans).
   
   I hope to change btree - it's possible, -
   but not hashes...

6. I'm not happy with current deadlock detection code!
   It seems that backend does DeadLockCheck each time
   when timer expired - shouldn't this be done _once_,
   before backend is going to sleep ?!

7. As I read in Sybase documentation the default 
   standard transaction mode is _chained_ - all
   queries before explicit COMMIT/ABORT are run in _single
   transaction_... But we have to use BEGIN/END to get it!
   This was not so bad for system with relation level locks,
   but now only the same row writes block one other and so
   chained mode seems more appropriate...
   
   Shouldn't we change default transaction mode now?
   And use option/SET TRANSACTION MODE to switch to
   un-chained mode if one like it?

Vadim

  2. Re: [HACKERS] MVCC works in serialized mode!

    Bruce Momjian <maillist@candle.pha.pa.us> — 1998-12-16T18:00:34Z

    > 6. I'm not happy with current deadlock detection code!
>    It seems that backend does DeadLockCheck each time
>    when timer expired - shouldn't this be done _once_,
>    before backend is going to sleep ?!

Not sure.  Now that I think of it, it makes sense that if I go to sleep,
a deadlock is not sudenly going to appear while I am asleep.  If a new
process causes a deadlock, the new process that causes it will see it.

I did not check when I went to sleep because I thought it may be too
cpu-intensive to do checking on every sleep, but now that I remember it,
it may be very trivial in cpu time to do the check on every sleep.

I recommend changing it to do it just before every sleep.  Let me know
if you want me to make the change.


-- 
  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

  3. Re: [HACKERS] MVCC works in serialized mode!

    Vadim Mikheev <vadim@krs.ru> — 1998-12-17T06:14:39Z

    Bruce Momjian wrote:
> 
> > 6. I'm not happy with current deadlock detection code!
> >    It seems that backend does DeadLockCheck each time
> >    when timer expired - shouldn't this be done _once_,
> >    before backend is going to sleep ?!
> 
> Not sure.  Now that I think of it, it makes sense that if I go to sleep,
> a deadlock is not sudenly going to appear while I am asleep.  If a new
> process causes a deadlock, the new process that causes it will see it.
> 
> I did not check when I went to sleep because I thought it may be too
> cpu-intensive to do checking on every sleep, but now that I remember it,
> it may be very trivial in cpu time to do the check on every sleep.
> 
> I recommend changing it to do it just before every sleep.  Let me know
> if you want me to make the change.

May be we could just reduce first sleep time (60 sec is too long),
do DeadLockCheck _only once_, after first SIGALARM, and after that
just sleep forever ?
Why do DeadLockCheck many times ?

Let's think more...

And please consider when lock conflict occures:

1. One process tries update row being updated by other.
2. When reading/writing hashes (I hope to change btrees to
   use new buffer context lock code, as heap access methods
   do, - this is short term locking without deadlocks and so -
   without using lockmanager).

Vadim

  4. Re: [HACKERS] MVCC works in serialized mode!

    Bruce Momjian <maillist@candle.pha.pa.us> — 1998-12-18T06:49:09Z

    > Bruce Momjian wrote:
> > 
> > > 6. I'm not happy with current deadlock detection code!
> > >    It seems that backend does DeadLockCheck each time
> > >    when timer expired - shouldn't this be done _once_,
> > >    before backend is going to sleep ?!
> > 
> > Not sure.  Now that I think of it, it makes sense that if I go to sleep,
> > a deadlock is not sudenly going to appear while I am asleep.  If a new
> > process causes a deadlock, the new process that causes it will see it.
> > 
> > I did not check when I went to sleep because I thought it may be too
> > cpu-intensive to do checking on every sleep, but now that I remember it,
> > it may be very trivial in cpu time to do the check on every sleep.
> > 
> > I recommend changing it to do it just before every sleep.  Let me know
> > if you want me to make the change.
> 
> May be we could just reduce first sleep time (60 sec is too long),

Yes, much too long.  5 or 15 seconds sounds good.

> do DeadLockCheck _only once_, after first SIGALARM, and after that
> just sleep forever ?
> Why do DeadLockCheck many times ?

Yes, no need to do many times.

OK.  Should I make the change?

> 
> Let's think more...
> 
> And please consider when lock conflict occures:
> 
> 1. One process tries update row being updated by other.
> 2. When reading/writing hashes (I hope to change btrees to
>    use new buffer context lock code, as heap access methods
>    do, - this is short term locking without deadlocks and so -
>    without using lockmanager).

Oh.  I would think even a 1 second deadlock detection would work well. 
Most short-term locks don't last that long.

-- 
  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

  5. Re: [HACKERS] MVCC works in serialized mode!

    Bruce Momjian <maillist@candle.pha.pa.us> — 1998-12-18T19:49:40Z

    > Bruce Momjian wrote:
> > 
> > > 6. I'm not happy with current deadlock detection code!
> > >    It seems that backend does DeadLockCheck each time
> > >    when timer expired - shouldn't this be done _once_,
> > >    before backend is going to sleep ?!
> > 
> > Not sure.  Now that I think of it, it makes sense that if I go to sleep,
> > a deadlock is not sudenly going to appear while I am asleep.  If a new
> > process causes a deadlock, the new process that causes it will see it.
> > 
> > I did not check when I went to sleep because I thought it may be too
> > cpu-intensive to do checking on every sleep, but now that I remember it,
> > it may be very trivial in cpu time to do the check on every sleep.
> > 
> > I recommend changing it to do it just before every sleep.  Let me know
> > if you want me to make the change.
> 
> May be we could just reduce first sleep time (60 sec is too long),
> do DeadLockCheck _only once_, after first SIGALARM, and after that
> just sleep forever ?
> Why do DeadLockCheck many times ?
> 
> Let's think more...
> 
> And please consider when lock conflict occures:
> 
> 1. One process tries update row being updated by other.
> 2. When reading/writing hashes (I hope to change btrees to
>    use new buffer context lock code, as heap access methods
>    do, - this is short term locking without deadlocks and so -
>    without using lockmanager).
> 
> Vadim
> 

I have applied the following patch.  It causes only one deadlock check
after a sleep of one second.  Applied only to the CURRENT tree.

-- 
  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

  6. Re: [HACKERS] MVCC works in serialized mode!

    Vadim Mikheev <vadim@krs.ru> — 1998-12-19T11:47:40Z

    Bruce Momjian wrote:
> 
> I have applied the following patch.  It causes only one deadlock check
> after a sleep of one second.  Applied only to the CURRENT tree.

Nice, at least for now.

Vadim

  7. RE: [HACKERS] MVCC works in serialized mode!

    Hiroshi Inoue <inoue@tpf.co.jp> — 1998-12-25T04:04:38Z

    Hi all,

> -----Original Message-----
> From: owner-pgsql-hackers@postgreSQL.org
> [mailto:owner-pgsql-hackers@postgreSQL.org]On Behalf Of Vadim Mikheev
> Sent: Wednesday, December 16, 1998 10:01 PM
> To: hackers@postgreSQL.org
> Subject: [HACKERS] MVCC works in serialized mode!
> 
> 
> CVS is just updated...
> 
> Please try concurrent writes/reads...
>

I happend to enjoy MVCC a little in (v6.4.1) .

Readers are never blocked and writers are blocked only by 
same row writers as I expected.
It's so comfortable.

But I have a question.
Once transactions are blocked,it takes so long time to resume 
after blocks were removed.
Why ?
Currently blocked transactions resume immediately after blocks 
were removed.

Thanks.

Hiroshi Inoue
Inoue@tpf.co.jp

  8. Re: [HACKERS] MVCC works in serialized mode!

    Bruce Momjian <maillist@candle.pha.pa.us> — 1998-12-25T04:07:04Z

    [Charset iso-8859-1 unsupported, filtering to ASCII...]
> Hi all,
> 
> > -----Original Message-----
> > From: owner-pgsql-hackers@postgreSQL.org
> > [mailto:owner-pgsql-hackers@postgreSQL.org]On Behalf Of Vadim Mikheev
> > Sent: Wednesday, December 16, 1998 10:01 PM
> > To: hackers@postgreSQL.org
> > Subject: [HACKERS] MVCC works in serialized mode!
> > 
> > 
> > CVS is just updated...
> > 
> > Please try concurrent writes/reads...
> >
> 
> I happend to enjoy MVCC a little in (v6.4.1) .

That's funny.

> 
> Readers are never blocked and writers are blocked only by 
> same row writers as I expected.
> It's so comfortable.

Wow, that is cool.


-- 
  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

  9. Re: [HACKERS] MVCC works in serialized mode!

    Vadim Mikheev <vadim@krs.ru> — 1998-12-25T05:39:32Z

    Hiroshi Inoue wrote:
> 
> >
> > CVS is just updated...
> >
> > Please try concurrent writes/reads...
> >
> 
> I happend to enjoy MVCC a little in (v6.4.1) .
> 
> Readers are never blocked and writers are blocked only by
> same row writers as I expected.
> It's so comfortable.
> 
> But I have a question.
> Once transactions are blocked,it takes so long time to resume
> after blocks were removed.
> Why ?
> Currently blocked transactions resume immediately after blocks
> were removed.

What do you mean?
Example please...

Vadim

  10. RE: [HACKERS] MVCC works in serialized mode!

    Hiroshi Inoue <inoue@tpf.co.jp> — 1998-12-25T06:09:04Z

    > -----Original Message-----
> From: root@dune.krs.ru [mailto:root@dune.krs.ru]On Behalf Of Vadim
> Mikheev
> Sent: Friday, December 25, 1998 2:40 PM
> To: Hiroshi Inoue
> Cc: hackers@postgreSQL.org
> Subject: Re: [HACKERS] MVCC works in serialized mode!
>
>
> Hiroshi Inoue wrote:
> >
> > >
> > > CVS is just updated...
> > >
> > > Please try concurrent writes/reads...
> > >
> >
> > I happend to enjoy MVCC a little in (v6.4.1) .
> >
> > Readers are never blocked and writers are blocked only by
> > same row writers as I expected.
> > It's so comfortable.
> >
> > But I have a question.
> > Once transactions are blocked,it takes so long time to resume
> > after blocks were removed.
> > Why ?
> > Currently blocked transactions resume immediately after blocks
> > were removed.
>
> What do you mean?
> Example please...
>

inoue=> create table t1 (key int,a int);
inoue=> insert into t1 values (1,0);

<Session-1>                                          <Session-2>

inoue=> begin;                                       inoue=> begin;
BEGIN                                                   BEGIN
inoue=> update t1 set a=1 where key=1;
UPDATE 1
                                                            inoue=> update
t1 set a=2 where key=1;


                                                                 [ blocked ]
inoue=> end/abort;
END/ABORT
                                                                   [ after
long time .... ]
                                                            ERROR:  Can't
serialize access due to concurrent update
                                                            / UPDATE 1


Thanks.

Hiroshi Inoue
Inoue@tpf.co.jp

  11. Re: [HACKERS] MVCC works in serialized mode!

    Vadim Mikheev <vadim@krs.ru> — 1998-12-25T08:06:40Z

    Hiroshi Inoue wrote:
> 
> > >
> > > But I have a question.
> > > Once transactions are blocked,it takes so long time to resume
> > > after blocks were removed.
> > > Why ?
> > > Currently blocked transactions resume immediately after blocks
> > > were removed.
> >
> > What do you mean?
> > Example please...
> >
> [ after long time .... ]
>         ERROR:  Can't serialize access due to concurrent update

Just tried (with CURRENT) - no problems...

Vadim

  12. Re: [HACKERS] MVCC works in serialized mode!

    Vadim Mikheev <vadim@krs.ru> — 1998-12-25T10:32:44Z

    > 
> 2. LOCK TABLE modes are not yet implemented...

Implemented, as well as SET TRANSACTION ISOLATION LEVEL...

> 
> 3. As well as SELECT ... FOR UPDATE: I need in advice here!
> 
>    Do Oracle, Informix etc support SELECT FOR UPDATE if
>    there are aggregates, group by, distinct in SELECT ???

As I see in Oracle documentation FOR UPDATE is disallowed
in these cases... No objections ?

>    Is SELECT FOR UPDATE allowed in subqueries ???

Could someone test this?

> 
> 7. As I read in Sybase documentation the default
>    standard transaction mode is _chained_ - all
>    queries before explicit COMMIT/ABORT are run in _single
>    transaction_... But we have to use BEGIN/END to get it!
>    This was not so bad for system with relation level locks,
>    but now only the same row writes block one other and so
>    chained mode seems more appropriate...
> 
>    Shouldn't we change default transaction mode now?
>    And use option/SET TRANSACTION MODE to switch to
>    un-chained mode if one like it?

No comments on this?
I would like to make BEGIN implicit...
Objections?

Vadim

  13. Re: [HACKERS] MVCC works in serialized mode!

    Bruce Momjian <maillist@candle.pha.pa.us> — 1998-12-25T11:29:52Z

    > > 
> > 7. As I read in Sybase documentation the default
> >    standard transaction mode is _chained_ - all
> >    queries before explicit COMMIT/ABORT are run in _single
> >    transaction_... But we have to use BEGIN/END to get it!
> >    This was not so bad for system with relation level locks,
> >    but now only the same row writes block one other and so
> >    chained mode seems more appropriate...
> > 
> >    Shouldn't we change default transaction mode now?
> >    And use option/SET TRANSACTION MODE to switch to
> >    un-chained mode if one like it?
> 
> No comments on this?
> I would like to make BEGIN implicit...
> Objections?

Informix requires BEGIN.  Ingres does not, but has 'set autocommit'
mode, so each SQL statement is its own transaction, like we have now.

I always felt that if I go in to psql and run a query, I want it
applied.  I don't want to have to commit every query I type.

I know I can use SET TRANSACTION MODE to change this.

What do others think?

-- 
  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

  14. Re: [HACKERS] MVCC works in serialized mode!

    Theo Kramer <theo@flame.co.za> — 1998-12-28T14:04:56Z

    Bruce Momjian wrote:
> > > 7. As I read in Sybase documentation the default
> > >    standard transaction mode is _chained_ - all
> > >    queries before explicit COMMIT/ABORT are run in _single
> > >    transaction_... But we have to use BEGIN/END to get it!
> > >    This was not so bad for system with relation level locks,
> > >    but now only the same row writes block one other and so
> > >    chained mode seems more appropriate...
> > >
> > >    Shouldn't we change default transaction mode now?
> > >    And use option/SET TRANSACTION MODE to switch to
> > >    un-chained mode if one like it?
> >
> > No comments on this?
> > I would like to make BEGIN implicit...
> > Objections?
> 
> Informix requires BEGIN.  Ingres does not, but has 'set autocommit'
> mode, so each SQL statement is its own transaction, like we have now.
> 
> I always felt that if I go in to psql and run a query, I want it
> applied.  I don't want to have to commit every query I type.
> 
> I know I can use SET TRANSACTION MODE to change this.
> 
> What do others think?

As long as we can switch. Interactive applications typically update more
than one objects per transaction.

--------
Regards
Theo

  15. Re: [HACKERS] MVCC works in serialized mode!

    Thomas Lockhart <lockhart@alumni.caltech.edu> — 1998-12-28T15:39:31Z

    > > No comments on this?
> > I would like to make BEGIN implicit...
> > Objections?
> Informix requires BEGIN.  Ingres does not, but has 'set autocommit'
> mode, so each SQL statement is its own transaction, like we have now.

imho we should have an Ingres-like feature for "autocommit". We can have
the default be "set autocommit on" (probably with an equals sign like
our other "set" variables) and we can have it be a run-time option like
DATESTYLE and other settable parameters. So you can configure your
server or your client environment to always behave the way you prefer.

I'd be happy to implement the syntax and the environment variable parts;
just need a global boolean value to check and set...

                     - Tom

  16. Q: CURSOR tuples count

    Vazsonyi Peter[ke] <neko@kornel.szif.hu> — 1999-01-04T16:01:48Z

    Hello!

I want to make a filtered selection on a table. This can return with many
tuples. The download of the query results may take a few  minutes. I'd like
to show the progress status. How can i do this?
If i run this in two query (first i count the number of lines, than the real
query), than the backend calculates the query two times.
If i use cursor, i can not get the line count before i fetch the whole table.

--
 So long and thanx for all the fish.
 NeKo@(kva.hu|kornel.szif.hu)

  17. Re: [HACKERS] MVCC works in serialized mode!

    Vadim Mikheev <vadim@krs.ru> — 1999-01-10T17:12:13Z

    "Thomas G. Lockhart" wrote:
> 
> > > No comments on this?
> > > I would like to make BEGIN implicit...
> > > Objections?
> > Informix requires BEGIN.  Ingres does not, but has 'set autocommit'
> > mode, so each SQL statement is its own transaction, like we have now.
> 
> imho we should have an Ingres-like feature for "autocommit". We can have
> the default be "set autocommit on" (probably with an equals sign like
> our other "set" variables) and we can have it be a run-time option like
> DATESTYLE and other settable parameters. So you can configure your
> server or your client environment to always behave the way you prefer.
> 
> I'd be happy to implement the syntax and the environment variable parts;
> just need a global boolean value to check and set...

Nice! TIA -:)

Could you also change configure stuff, to choose default mode
before compiling?

Vadim

  18. Re: [HACKERS] MVCC works in serialized mode!

    Thomas Lockhart <lockhart@alumni.caltech.edu> — 1999-01-10T17:42:29Z

    > > imho we should have an Ingres-like feature for "autocommit".
> Nice! TIA -:)

Sure, but if I do too much work on this I'll need you to help on outer
joins :) (Actually, that's just an excuse; I'm flailing on it trying to
understand things you already know.)

Is there a global boolean "autocommit flag" already there to work with,
or could you add one? I'd like to (if possible) keep from getting sucked
into non-parser/non-docs work until I've worked out some of the outer
join stuff. But I can do the parser and "set autocommit" stuff. Also,
I'd like to go through the gram.y code for the new MVCC support commands
and have it use parser keywords rather than "Ident" entities for the
syntax. OK?

> Could you also change configure stuff, to choose default mode
> before compiling?

I'll set things up for it in the code, and perhaps Tom Lane or someone
can help with the configure support. We can ask when it's time...

                 - Tom