Обсуждение: select 'x' ~ repeat('x*y*z*', 1000);

Hi,

Just an observation: on REL_13_STABLE, $SUBJECT maps in ~170MB of
memory, and on master it's ~204MB.  A backend running that was just
nuked by the kernel due to lack of swap space on my tiny buildfarm
animal elver (a VM with 1GB RAM, 2GB swap, not doing much else).
Could also be related to an OS upgrade ~1 week ago.  It's obviously
time to increase the VM size which is no problem, but I thought those
numbers were interesting.

Thomas Munro <thomas.munro@gmail.com> writes:
> Just an observation: on REL_13_STABLE, $SUBJECT maps in ~170MB of
> memory, and on master it's ~204MB.  A backend running that was just
> nuked by the kernel due to lack of swap space on my tiny buildfarm
> animal elver (a VM with 1GB RAM, 2GB swap, not doing much else).

Yeah, that's not terribly surprising.  Note that the point of that
test case is to fail: it's supposed to verify that we apply the
REG_MAX_COMPILE_SPACE limit and error out before hitting a kernel
OOM condition.  When I redid regex memory allocation in 0fc1af174,
there was a question of how to map the old complexity limit to the
new one.  I went with

 #define REG_MAX_COMPILE_SPACE  \
-   (100000 * sizeof(struct state) + 100000 * sizeof(struct arcbatch))
+   (500000 * (sizeof(struct state) + 4 * sizeof(struct arc)))
 #endif

knowing that that was a bit of a scale-up of the limit, but intending
that we'd not fail on any case that worked before.  We could knock
down the 500000 multiplier a little, but I'm afraid we'd lose the
it-still-works property, because the edge cases are a little different
for the new code than the old.

            regards, tom lane