Josef “Jeff” Sipek

MongoDB - First Impressions

I just ssh’ed into a server that’s running MongoDB to see if it was doing anything and if there were any cool commands to get stats from it. (I’ve never used MongoDB.) I accidentally ran mongod as non-root. It died because it didn’t have the right permissions — good. However, something in the output seemed completely and utterly retarded.

warning: 32-bit servers don't have journaling enabled by default. Please use
	--journal if you want durability.

[initandlisten] MongoDB starting : pid=12682 port=27017 dbpath=/data/db/
	32-bit host=hkn2012
[initandlisten] ** NOTE: when using MongoDB 32 bit, you are limited to about
	2 gigabytes of data
[initandlisten] **       see
[initandlisten] **       with --journal, the limit is lower

Was it the 2 GB data limit? Nope! Was it the fact that 32-bit systems default to non-durable mode while 64-bit default to durable? Bingo! Seriously, that is retarded. Why would anyone think that it is a good idea to cripple 32-bit systems like that? Was performance so bad with journaling that to avoid gaining a reputation for being slow the developers decided to keep the data unsafe by default? I doubt it. Was it to squeeze in a couple more MB of addressable data? Probably. Good job, folks.

For what it is worth, I decided to see if the 2 GB limit was something silly (i.e., using an int in some on-disk structure). It turns out that mongod likes to mmap the data for fast access. This is reasonable. (More so than using architecture specific integral types in on-disk structures.)

I wonder what other gems are hiding in this software.

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