db_dump is inefficient

[Nicolas]

Let's compare.

• Write a potentially big uncompressed XML file (over 2GB for SETI@Home), then use system() to run gzip on it (which reads it again, writes something like 300MB, then deletes the original that took so long to write). Total I/O: 2GB read, 2.3GB write, plus the database reads (which are quite a lot too).
• Use zlib to write the file in compressed form in the first place. I/O: 300MB write, plus database reads.

Which would you choose?

I'll see if I can modify db_dump myself to use zlib, and post the patch. Otherwise, anyone is free to take the task.