Re: Small SSI issues

On Tue, Jul 5, 2011 at 12:03 PM, Kevin Grittner
<Kevin(dot)Grittner(at)wicourts(dot)gov> wrote:
> Robert Haas <robertmhaas(at)gmail(dot)com> wrote:
>
>> Well, as long as we can verify that OLDSERXID_MAX_PAGE has the
>> same value for BLCKSZ=8K before and after this patch, I don't see
>> any real downside to applying it.  If, hypothetically, it's buggy,
>> it's only going to break things for non-default block sizes which
>> are, by your description, not correct right now anyway.
>
> Outside of a code comment, the entire patch consists of replacing
> the definition of the OLDSERXID_MAX_PAGE macro.  The old definition
> is:
>
>  (SLRU_PAGES_PER_SEGMENT * 0x10000 - 1)
>
> SLRU_PAGES_PER_SEGMENT is define to be 32.  So this is:
>
>  (32 * 0x10000) - 1 = 2097151
>
> The new definition is the min of the old one and a value based on
> BLCKSZ:
>
>  (MaxTransactionId + 1) / OLDSERXID_ENTRIESPERPAGE - 1)
>
> Where "entries per page" is BLCKSZ / sizeof(uint64).
>
> For an 8K BLCKSZ this is:
>
>  ((0xffffffff + 1) / 1024) - 1 = 4194303
>
> So the macro is guaranteed to have the same value as it currently
> does for BLCKSZ of 16KB or lower.

I went ahead and committed this.

--
Robert Haas
EnterpriseDB: http://www.enterprisedb.com
The Enterprise PostgreSQL Company