Qingqing Zhou <[EMAIL PROTECTED]> wrote: > To reduce size of varlen2.vl_len to int16. This has been mentioned before, > but is there any show-stopper reasoning preventing us from doing that or > somebody has been working on it?
Hi, I'm rewriting the patch that I proposed before. (http://archives.postgresql.org/pgsql-hackers/2005-09/msg00421.php) This is another way to reduce the size of variable length types, using variable length headers. I'm sure that there are pros and cons of this approach. Pros. - Optimized for short variables (length <= 127), where the header takes only one byte. - It can represent long data. Cons. - More complexity and operations to extract lengths and buffers. - Needs more works to support TOAST. To support TOAST, I think the following representations. It might be good to use only A and B, if TOAST is not needed. | Representation | Size | Mode | --+----------------------------+-------+---------------------+ A | 0******* + data | 1 + n | length <= 127 | B | 10****** + 1 byte + data | 2 + n | length <= 16K -1 | C | 110----- + 4 bytes + data | 5 + n | length <= 4G -1 | D | 1110---- + 6 bytes + data | 7 + n | Compressed | E | 11110--- + 12 bytes | 13 | External | F | 11111--- + 16 bytes | 17 | External+Compressed | ('*' bits are used for length, '-' are unused.) Comments welcome, --- ITAGAKI Takahiro NTT Cyber Space Laboratories ---------------------------(end of broadcast)--------------------------- TIP 2: Don't 'kill -9' the postmaster
