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Thread: Lock structures

Lock structures

From
Bruce Momjian
Date:
Can someone explain why LockMethodCtl is in shared memory while
LockMethodTable is in postmaster memory context?

I realize LockMethodCtl has a spinlock, so it has to be in shared
memory, but couldn't it all be put in shared memory?

Also, the code:

LockShmemSize(int maxBackends)
{   int         size = 0;
   size += MAXALIGN(sizeof(PROC_HDR)); /* ProcGlobal */   size += MAXALIGN(maxBackends * sizeof(PROC));       /* each
MyProc*/  size += MAXALIGN(maxBackends * sizeof(LOCKMETHODCTL));      /* each
                    * lockMethodTable->ctl */
 

Is there one LOCKMETHODCTL for every backend?  I thought there was only
one of them.

--  Bruce Momjian                        |  http://candle.pha.pa.us pgman@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

Re: Lock structures

From
Tom Lane
Date:
Bruce Momjian <pgman@candle.pha.pa.us> writes:
> Can someone explain why LockMethodCtl is in shared memory while
> LockMethodTable is in postmaster memory context?
> I realize LockMethodCtl has a spinlock, so it has to be in shared
> memory, but couldn't it all be put in shared memory?

I think the original point was not to assume that the shared-memory
pointers would be the same in each backend.  Right now we don't need
that, but I see no good reason to change the data structure.

>     size += MAXALIGN(maxBackends * sizeof(LOCKMETHODCTL));      /* each
>                                                                  * lockMethodTable->ctl */

> Is there one LOCKMETHODCTL for every backend?  I thought there was only
> one of them.

You're right, that line is erroneous; it should read
   size += MAX_LOCK_METHODS * MAXALIGN(sizeof(LOCKMETHODCTL));

Not a significant error but it should be changed for clarity ...
        regards, tom lane

Re: Lock structures

From
Tom Lane
Date:
Bruce Momjian <pgman@candle.pha.pa.us> writes:
> Tom, what about the names?  There is LOCKMETHODCTL, LOCKMETHODTABLE,
> and LOCKMODES.   How about LOCKSTYLESHARED, LOCKSTYLE, and leave
> LOCKMODES unchanged?

I think both of those names are worse (less descriptive) than what
we have ...
        regards, tom lane

Re: Lock structures

From
Bruce Momjian
Date:
> Bruce Momjian <pgman@candle.pha.pa.us> writes:
> > Is there one LOCKMETHODCTL for every backend?  I thought there was only
> > one of them.
> >> 
> >> You're right, that line is erroneous; it should read
> >> 
> >> size += MAX_LOCK_METHODS * MAXALIGN(sizeof(LOCKMETHODCTL));
> >> 
> >> Not a significant error but it should be changed for clarity ...
> 
> > I assume the fix should be done in 7.2, not 7.1, right?
> 
> I see no reason to put it off ...
> 

Thanks.  Fix applied.

--  Bruce Momjian                        |  http://candle.pha.pa.us pgman@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

Re: Lock structures

From
Bruce Momjian
Date:
> > Is there one LOCKMETHODCTL for every backend?  I thought there was only
> > one of them.
> 
> You're right, that line is erroneous; it should read
> 
>     size += MAX_LOCK_METHODS * MAXALIGN(sizeof(LOCKMETHODCTL));
> 
> Not a significant error but it should be changed for clarity ...

I assume the fix should be done in 7.2, not 7.1, right?

--  Bruce Momjian                        |  http://candle.pha.pa.us pgman@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

Re: Lock structures

From
Tom Lane
Date:
Bruce Momjian <pgman@candle.pha.pa.us> writes:
> Is there one LOCKMETHODCTL for every backend?  I thought there was only
> one of them.
>> 
>> You're right, that line is erroneous; it should read
>> 
>> size += MAX_LOCK_METHODS * MAXALIGN(sizeof(LOCKMETHODCTL));
>> 
>> Not a significant error but it should be changed for clarity ...

> I assume the fix should be done in 7.2, not 7.1, right?

I see no reason to put it off ...
        regards, tom lane

Re: Lock structures

From
Bruce Momjian
Date:
> Bruce Momjian <pgman@candle.pha.pa.us> writes:
> > Is there one LOCKMETHODCTL for every backend?  I thought there was only
> > one of them.
> >> 
> >> You're right, that line is erroneous; it should read
> >> 
> >> size += MAX_LOCK_METHODS * MAXALIGN(sizeof(LOCKMETHODCTL));
> >> 
> >> Not a significant error but it should be changed for clarity ...
> 
> > I assume the fix should be done in 7.2, not 7.1, right?
> 
> I see no reason to put it off ...

Tom, what about the names?  There is LOCKMETHODCTL, LOCKMETHODTABLE,
and LOCKMODES.   How about LOCKSTYLESHARED, LOCKSTYLE, and leave
LOCKMODES unchanged?

--  Bruce Momjian                        |  http://candle.pha.pa.us pgman@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