Re: pg_dump -Fd and compression level

From: Marc Mamin <M(dot)Mamin(at)intershop(dot)de>
To: Andrew Dunstan <andrew(at)dunslane(dot)net>
Cc: PostgreSQL Hackers <pgsql-hackers(at)postgresql(dot)org>
Subject: Re: pg_dump -Fd and compression level
Date: 2015-07-27 07:52:00
Message-ID: B6F6FD62F2624C4C9916AC0175D56D8828C1869D@jenmbs01.ad.intershop.net
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>>>
>>> As per attached patch.
>>>
>>> Comments?
>>
>> It seems that the first test on the compression in pg_backup_tar.c is now obsolete.
>> It didn't make much sense anyway.
>>
>>
>>
>> 211 if (AH->compression < 0 || AH->compression > 9)
>> 212 AH->compression = Z_DEFAULT_COMPRESSION;
>> 213
>> 214 /* Don't compress into tar files unless asked to do so */
>> 215 if (AH->compression == Z_DEFAULT_COMPRESSION)
>> 216 AH->compression = 0;
>> 217
>> 218 /*
>> 219 * We don't support compression because reading the files back is not
>> 220 * possible since gzdopen uses buffered IO which totally screws file
>> 221 * positioning.
>> 222 */
>> 223 if (AH->compression != 0)
>> 224 exit_horribly(modulename,
>> 225 "compression is not supported by tar archive format\n");
>> 226 }
>>
>>
>
>In fact, the first two tests look unnecessary. Neither condition should
>be possible now.
>

Hello,

Isn't the second test still required if you call pg_dump -Ft without setting -Z0 explicitly ?
(=> AH->compression == Z_DEFAULT_COMPRESSION)

There still are a few suspicious places in pg_backup_tar.c
that refer to the compression although not supported (except for blob ?)
(C programming is beyond my capabilities, I can roughly read simple code ... )

regards,
Marc Mamin

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