Re: xl_heap_header alignment?

Hi, 

On July 21, 2020 10:45:37 AM PDT, Antonin Houska  wrote:
>I don't quite understand this part of the comment of the xl_heap_header
>structure:
>
>* NOTE: t_hoff could be recomputed, but we may as well store it because
> * it will come for free due to alignment considerations.
>
>What are the alignment considerations? The WAL code does not appear to
>assume
>any alignment, and therefore it uses memcpy() to copy the structure
>into a
>local variable before accessing its fields. For example,
>heap_xlog_insert().

Unless you declare them as packed, structs will add padding to align members correctly (if, and only if, the whole struct is stored well aligned).

Regards,

Andres
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