From: | Vignesh Raghunathan <vignesh(dot)pgsql(at)gmail(dot)com> |
---|---|
To: | pgsql-hackers(at)postgresql(dot)org |
Subject: | Size of TOAST pointer |
Date: | 2015-07-16 22:36:54 |
Message-ID: | CAD_AmVgQ6cHwCM_JoHH_vJmcLT6Q4tssNois1Un4AB=uXfVEBA@mail.gmail.com |
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Lists: | pgsql-hackers |
Hello,
I was looking at the documentation for TOAST (
http://www.postgresql.org/docs/devel/static/storage-toast.html) and it's
specified that the toast pointer occupies 18 bytes. However, the struct
representing the toast pointer is defined as follows
typedef struct varatt_external
{
int32 va_rawsize; /* Original data size
(includes header) */
int32 va_extsize; /* External saved size
(doesn't) */
Oid va_valueid; /* Unique ID of
value within TOAST table */
Oid va_toastrelid; /* RelID of TOAST table
containing it */
} varatt_external;
Assuming that the pointer is aligned to a 4 byte boundary, doesn't it sum
up to 16 bytes?
Could someone please explain why the documentation specifies it as 18 bytes?
I am pretty new to the source code and the C language in general so I
apologize if this question has an obvious answer.
Thanks,
Vignesh.
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