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Could you clarify on 2? I mean, there's of course a per-row overhead on a DB, but many rows get put into the same page - so I'm not sure how that's remotely as

Could you clarify on 2? I mean, there's of course a per-row overhead on a DB, but many rows get put into the same page - so I'm not sure how that's remotely as wasteful as a hypothetical filesystem that uses a minimum of a page-per-file. Of course, that's not a requirement for FS behaviour - just historically a lot of them have worked that way. > Reading/writing data from a database requires syscalls too Not for stuff that's in the DB's page cache. > Arguably the database is duplicating the caching logic of the OS and slows things down. That's a pretty biased assessment. A 'real' database like Postgres will use calls that bypass the OS page cache, so there's no duplication there. It also understands its usage patterns better, so it can do generally better than a general-purpose cache. > and rename is atomic Assuming your file system doesn't atomically give you a truncated file post-system-crash :-). > (Also note SQL is crap; it's a bad serialization of a data structure.) Agreed that SQL is not the best language, but is this an argument against set-based query languages, or just SQL specifically? Databases make some things that are really hard less hard. Managing concurrent read/writes over sets of files (say) is currently difficult. Sure, your FS could have deadlock detection, MVCC and so on built into it, but that would be turning the file system into even more of a database system than it already is. Database systems are complicated because people often want to do complicated things.

read 13y ago
A way to execute set-based queries is a major point you bring up here. It's also the most baffling. When tens of filesystems with sophisticated features completely omit what is one of the most common features used by database users, presumably it's not because filesystem designers are not capable of implementing it but of some more mundane reason. > Not for stuff that's in the DB's page cache. The database has to log what was written. It does use syscalls to write the write-ahead log. Agreed it can save read syscalls. Then again one process sending a query to another process to read something generates even more syscalls than having everything (app+db) all in the same process. You are right about 2. I'm playing devils advocate here jumping around assumptions. I could ask why you assume an OS will use a page per file, you can say Linux does this, I can say why is your OS so heavy and point to Exokernel, you can say that's side-stepping the issue. I could say user-space filesystem having its own page cache; in the end we are talking about the same thing. In the end: the less layers the better. When I look at the kernel I see something like the Berlin wall. A barrier that was there since you were born and which you never asked for. A kernel being hard to hack and monolithic is bound to push developers away, but it won't stop developers from building what they want in the end.

read 13y ago

A way to execute set-based queries is a major point you bring up here. It's also the most baffling. When tens of filesystems with sophisticated features completely omit what is one of the most common features used by database users, presumably it's not because filesystem designers are not capable of implementing it but of some more mundane reason. > Not for stuff that's in the DB's page cache. The database has to log what was written. It does use syscalls to write the write-ahead log. Agreed it can save read syscalls. Then again one process sending a query to another process to read something generates even more syscalls than having everything (app+db) all in the same process. You are right about 2. I'm playing devils advocate here jumping around assumptions. I could ask why you assume an OS will use a page per file, you can say Linux does this, I can say why is your OS so heavy and point to Exokernel, you can say that's side-stepping the issue. I could say user-space filesystem having its own page cache; in the end we are talking about the same thing. In the end: the less layers the better. When I look at the kernel I see something like the Berlin wall. A barrier that was there since you were born and which you never asked for. A kernel being hard to hack and monolithic is bound to push developers away, but it won't stop developers from building what they want in the end.