gzcompress produces longer data because it embeds information about the encoding onto the string. If you are compressing data that will only ever be handled on one machine, then you don't need to worry about which of these functions you use. However, if you are passing data compressed with these functions to a different machine you should use gzcompress.
(PHP 4 >= 4.0.4, PHP 5)
gzdeflate — Deflate a string
$level= -1 [, int
$encoding= ZLIB_ENCODING_RAW ]] )
This function compress the given string using the DEFLATE data format.
For details on the DEFLATE compression algorithm see the document "» DEFLATE Compressed Data Format Specification version 1.3" (RFC 1951).
The data to deflate.
The level of compression. Can be given as 0 for no compression up to 9 for maximum compression. If not given, the default compression level will be the default compression level of the zlib library.
The deflated string or
FALSE if an error occurred.
Example #1 gzdeflate() example
$compressed = gzdeflate('Compress me', 9);
running 50000 repetitions on various content, i found that gzdeflate() and gzcompress() both performed equally fast regardless content and compression level, but gzinflate() was always about twice as fast as gzuncompress().
gzcompress() is the same like gzdefflate(), it produces identical data and its speed is the same as well. The only difference is that gzcompress produces 6 bytes bigger result (2 extra bytes at the beginning and 4 extra bytes at the end).
Take care that that "PHP deflate" != "HTTP deflate".
The deflate encoding used in HTTP is actually zlib encoded.
This is what PHP functions return:
gzencode() == gzip
gzcompress() == zlib (aka. HTTP deflate)
gzdeflate() == *raw* deflate encoding
if you have compressed data which is greater than 2 MB (system dependent), you will receive a buffer error by calling the function gzinflate().
be sure to to compress your data by a lower compression level, like 1.
i.e.: gzdeflate($sData, 1);
@ giunta dot gaetano at sea-aeroportimilano dot it
No, gzdeflate() implements rfc1951.
And rf2616 (http 1.1 specs) says "deflate : The "zlib" format defined in RFC 1950  in combination with the "deflate" compression mechanism described in RFC 1951 ."