Re: Re: COPY BINARY file format proposal
От | Philip Warner |
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Тема | Re: Re: COPY BINARY file format proposal |
Дата | |
Msg-id | 3.0.5.32.20001207133403.02d6acc0@mail.rhyme.com.au обсуждение исходный текст |
Ответ на | Re: Re: COPY BINARY file format proposal (Tom Lane <tgl@sss.pgh.pa.us>) |
Ответы |
Re: Re: COPY BINARY file format proposal
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Список | pgsql-hackers |
At 21:12 6/12/00 -0500, Tom Lane wrote: >Philip Warner <pjw@rhyme.com.au> writes: >>> OK, we can do it that way. I'm still going to pick a magic number that >>> looks different depending on endianness, however ;-). > >> What does the smiley mean in this context? > >Just thinking that the only way an endianness flag inside the header >would be useful is if we pick a magic number that's a bytewise >palindrome. You could just read the 1st, 2nd, 3rd, etc bytes and require that they be 'P', 'G', 'C', 'P', 'Y' or some such. I *think* reading five bytes and doing a strcmp works...ie. don't rely on the integer value, use a string. >> - floating point representation (for portability) > >Specified how? (For that matter, determined how?) I'd recommend a crystal ball. You did ask a question about the future ;-}. >> - flag for compressed or uncompressed toast fields (I assume you dump them >> uncompressed?) > >Yes, I want COPY to force 'em to uncompressed so as to avoid problems >with cross-version changes of compression algorithm. (Right at the >moment it gets that wrong.) Sounds reasonable, but there could be an advantage in allowing a binary compressed dump for short-term work. >> - version number may be important if we dump a subset of fields (ie. we'll >> need to store the field names somewhere). > >No we don't. ASCII COPY format doesn't store field names either ... at >least not as part of the data stream ... and should not IMHO. Don't you >want to be able to reload into a table that you've changed the column >names of? This is essential if we ever allow subsets of columns - even if it is only for displaying information to the user. If I dump 5 out of 7 columns then rename half of them, I'd say I'm asking for trouble. At least with the names available, you have a chance of working out what goes where. But again, without copy-a-subset-of-columns, this also requires a crystal ball. It all gets back to whether it's a good idea to overload a magic number. ---------------------------------------------------------------- Philip Warner | __---_____ Albatross Consulting Pty. Ltd. |----/ - \ (A.B.N. 75 008 659 498) | /(@) ______---_ Tel: (+61) 0500 83 82 81 | _________ \ Fax: (+61) 0500 83 82 82 | ___________ | Http://www.rhyme.com.au | / \| | --________-- PGP key available upon request, | / and from pgp5.ai.mit.edu:11371 |/
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