Keith Wiley 2012-03-19, 22:51
>From my experience, if you can fit data in a SQL without sharding or
anything, don't ever think twice. Hive is not even comparable.
I would rather say that Hive is a nice SQL interface over Hadoop M/R rather
than any SQL replacement. If you are running a DWH in SQL and you don't
need to grow your data to at least a couple of Tb, then keep SQL. The very
nice feature of Hadoop/Hive is that your DWH can grow (almost) horizontally
without much trouble by buying new servers, and most of your queries scale
with the number of servers too.
You have to know that doing a SELECT count(1) FROM t where t is ~1Gb can
take more time to start/stop the M/R job which has huge overhead than to
actually count. A simple wc -l takes about a second on any normal PC.
On Mon, Mar 19, 2012 at 11:51 PM, Keith Wiley <[EMAIL PROTECTED]> wrote:
> I haven't had an opportunity to set up a huge Hive database yet because
> exporting csv files from our SQL database is, in itself, a rather laborious
> task. I was just curious how I might expect Hive to perform vs. SQL on
> large databases and large queries? I realize Hive is pretty "latent" since
> it builds and runs MapReduce jobs for even the simplest queries, but that
> is precisely why I think it might perform better on long queries against
> large (external CSV) databases).
> Would you expect Hive to ever outperform SQL on a single machine
> (standalone or pseudo-distributed mode)? I am entirely open to the
> possibility that the answer is no, that Hive could never compete with SQL
> in a single machine. Is this true?
> If so, how large (how parallel) do you think the underlying Hadoop cluster
> needs to be before Hive overtakes SQL? 2X? 10X? Where is the crossover
> point where Hive actually outperforms SQL?
> Along similar lines, might Hive never outperform SQL on a database small
> enough for SQL to run on a single machine, a 10s to 100s of GBs? Must the
> database itself be so large that SQL is effectively crippled and the data
> must be distributed before Hive offer significant gains?
> I am really just trying to get a basic feel for how I might anticipate's
> Hive's behavior vs. SQL once I get a large system up and running.
> Keith Wiley [EMAIL PROTECTED] keithwiley.com
> "I used to be with it, but then they changed what it was. Now, what I'm
> isn't it, and what's it seems weird and scary to me."
> -- Abe (Grandpa) Simpson
Keith Wiley 2012-03-20, 06:02