>Are there any other flag bits that we should or are planning to add into WAL 
>header newly, except the above two? If yes and they are required by even a 
>block which doesn't have an image, I will change my mind and agree to add 
>something like chunk ID to a block header. 
>But I guess the answer of the question is No. Since the flag bits now we are 
>thinking to add are required only by a block having an image, adding them into 
>a block header (instead of block image header) seems a waste of bytes in WAL. 
>So I concur with Michael.
I agree.
As per my understanding, this change of xlog format was to provide for future 
enhancement which would need flags relevant to entire block.
But as mentioned, currently the flags being added are related to block image 
only. Hence for this patch it makes sense to add a field to 
XLogRecordImageHeader rather than block header. 
This will also save bytes per WAL record. 

Thank you,
Rahila Syed


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