I have never seen the oom-killer before. I had heard stories from battle hardened veterans about their tussles with the beast but these stories where all just myths to me, until today, when the beastie raised its head in my logs.
Dec 20 18:08:50 debian kernel: oom-killer: gfp_mask=0x1d2
59071 Dec 20 18:08:51 debian kernel: DMA per-cpu:
59072 Dec 20 18:08:51 debian kernel: cpu 0 hot: low 2, high 6, batch 1
59073 Dec 20 18:08:51 debian kernel: cpu 0 cold: low 0, high 2, batch 1
59074 Dec 20 18:08:51 debian kernel: Normal per-cpu:
59075 Dec 20 18:08:51 debian kernel: cpu 0 hot: low 32, high 96, batch 16
59076 Dec 20 18:08:51 debian kernel: cpu 0 cold: low 0, high 32, batch 16
59077 Dec 20 18:08:51 debian kernel: HighMem per-cpu:
59078 Dec 20 18:08:51 debian kernel: cpu 0 hot: low 14, high 42, batch 7
59079 Dec 20 18:08:51 debian kernel: cpu 0 cold: low 0, high 14, batch 7
59080 Dec 20 18:08:51 debian kernel:
59081 Dec 20 18:08:51 debian kernel: Free pages: 1040kB (112kB HighMem)
59082 Dec 20 18:08:51 debian kernel: Active:253987 inactive:249 dirty:0 writeback:5 unstable:0 free:260 slab:2326 mapped:254 013 pagetables:680
59083 Dec 20 18:08:52 debian kernel: DMA free:16kB min:16kB low:32kB high:48kB active:12296kB inactive:0kB present:16384kB
59084 Dec 20 18:08:52 debian kernel: protections[]: 0 0 0
59085 Dec 20 18:08:52 debian kernel: Normal free:912kB min:936kB low:1872kB high:2808kB active:873984kB inactive:996kB prese nt:901120kB
59086 Dec 20 18:08:52 debian kernel: protections[]: 0 0 0
59087 Dec 20 18:08:52 debian kernel: HighMem free:112kB min:128kB low:256kB high:384kB active:129668kB inactive:0kB present: 131008kB
59088 Dec 20 18:08:52 debian kernel: protections[]: 0 0 0
59089 Dec 20 18:08:52 debian kernel: DMA: 0*4kB 0*8kB 1*16kB 0*32kB 0*64kB 0*128kB 0*256kB 0*512kB 0*1024kB 0*2048kB 0*4096k B = 16kB
59090 Dec 20 18:08:52 debian kernel: Normal: 0*4kB 0*8kB 1*16kB 2*32kB 1*64kB 0*128kB 1*256kB 1*512kB 0*1024kB 0*2048kB 0*40 96kB = 912kB
59091 Dec 20 18:08:52 debian kernel: HighMem: 0*4kB 0*8kB 1*16kB 1*32kB 1*64kB 0*128kB 0*256kB 0*512kB 0*1024kB 0*2048kB 0*4 096kB = 112kB
59092 Dec 20 18:08:52 debian kernel: Swap cache: add 848298, delete 845230, find 151472/187493, race 0+3
59093 Dec 20 18:08:52 debian kernel: Out of Memory: Killed process 6332 (postmaster).
It would appear I was being a bit greedy with Postgres.