Newbe Dev Stack

Answer : VACUUM is only needed on updated or deleted rows in non-temporary tables. Obviously you're doing lots of INSERTs but it's not obvious from the description that you're also doing lots of UPDATEs or DELETEs. These operations can be tracked with the pg_stat_all_tables view, specifically the n_tup_upd and n_tup_del columns. Also, even more to the point, there is a n_dead_tup column that tells, per table, how much rows need to be vacuumed. (see Monitoring statistics in the doc for functions and views related to statistics gathering). A possible strategy in your case would be to suppress the scheduled VACUUM, keeping an eye on this view and checking on which tables the n_dead_tup is going up significantly. Then apply the aggressive VACUUM to these tables only. This will be a win if there are large tables whose rows never get deleted nor updated and the aggressive VACUUM is really necessary only on smaller tables. But keep running the ANALYZE for the optimiz...

Answer : The conductivity of the vacuum is not a very trivial issue. In fact, depending on how you look at it, it behaves in two different ways. Firstly, there is no retarding force on any charged particle with constant velocity in vacuum. To this extent, no extra work is required in maintaining a constant current through any surface in vacuum. In stark contrast however, is the presence of free charges in conductors. Normally, when an electric field E \mathbf{E} E is applied across a conductor, we get a current density due to the 'internal' charge flow, given by: J = σ E \mathbf{J} = \sigma\mathbf{E} J = σ E where σ \sigma σ is the conductivity. Clearly, σ = 0 \sigma = 0 σ = 0 in a vacuum - electric fields do not spontaneously cause currents to flow. Thus, in this sense, the vacuum is not a conductor at all. Even everyday insulators have low but non-zero values of σ \sigma σ . Thus, the resistance of the vacuum is in fact, infinite, as long as we define resistance ...