Re: pageinspect patch, for showing tuple data - Mailing list pgsql-hackers

On Thu, Oct 1, 2015 at 8:13 PM, Nikolay Shaplov wrote:
> В письме от 30 сентября 2015 13:49:00 пользователь Michael Paquier написал:
>>
>> -                                 errmsg("input page too small (%d bytes)",
>> raw_page_size)));
>> +                                        errmsg("input page too small (%d
>> bytes)", raw_page_size)));
>> Please be careful of spurious diffs. Those just make the life of committers
>> more difficult than it already is.
>
> Oh, that's not diff. That's I've fixed indent on the code I did not write :-)

pgindent would have taken care of that if needed. There is no need to add noise in the code for this patch.

>> +     <para>
>> +     General idea about output columns: <function>lp_*</function>
>> attributes
>> +     are about where tuple is located inside the page;
>> +     <function>t_xmin</function>, <function>t_xmax</function>,
>> +     <function>t_field3</function>, <function>t_ctid</function> are about
>> +     visibility of this tuplue inside or outside of the transaction;
>> +     <function>t_infomask2</function>, <function>t_infomask</function> has
>> some
>> +     information about properties of attributes stored in tuple data.
>> +     <function>t_hoff</function> sais where tuple data begins and
>> +     <function>t_bits</function> sais which attributes are NULL and which
>> are
>> +     not. Please notice that t_bits here is not an actual value that is
>> stored
>> +     in tuple data, but it's text representation  with '0' and '1'
>> charactrs.
>> +     </para>
>> I would remove that as well. htup_details.h contains all this information.
> Made it even more shorter. Just links and comments about representation of
> t_bits.

I would completely remove this part.

> There also was a bug in original pageinspect, that did not get t_bits right
> when there was OID in the tuple.  I've fixed it too.

Aha. Good catch! By looking at HeapTupleHeaderGetOid if the tuple has an OID it will be stored at the end of HeapTupleHeader and t_hoff includes it, so bits_len is definitely larger of 4 bytes should an OID be present.
               if (tuphdr->t_infomask & HEAP_HASNULL)
               {
-                       bits_len = tuphdr->t_hoff -
-                           offsetof(HeapTupleHeaderData, t_bits);
+                      int     bits_len =
+                          ((tuphdr->t_infomask2 & HEAP_NATTS_MASK)/8 + 1)*8;
 
                        values[11] = CStringGetTextDatum(
-                                           bits_to_text(tuphdr->t_bits, bits_len * 8));
+                                          bits_to_text(tuphdr->t_bits, bits_len));
                                }
And here is what you are referring to in your patch. I think that we should instead check for HEAP_HASOID and reduce bits_len by the size of Oid should one be present. As this is a bug that applies to all the existing versions of Postgres it would be good to extract it as a separate patch and then apply your own patch on top of it instead of including in your feature. Attached is a patch, this should be applied down to 9.0 I guess. Could you rebase your patch on top of it?

> Here is next patch in attachment.

--
Michael