sql: in cockroach demo, disk spilling produces confusing error message

[solongordon]

If a query in cockroach demo attempts to spill to disk, it throws a confusing already using disk error, presumably because we try to spill but there is zero budget for it.

Repro:

$ cockroach demo <<EOF
create table t (x int, y text, index (x, y));
create table t2 (x int);
insert into t select 1, repeat('a', 1024) from generate_series(1, 200000);
insert into t2 values (1);
select distinct y from t2 inner lookup join t on t.x = t2.x;
EOF

Result:

Error: pq: already using disk
Failed running "demo"

It seems fine for demo not to support spilling, but we should make this clearer in the error message.

[knz]

I think disk spilling has been enabled for cockroach demo. I get the following message:

ERROR: this query requires additional disk space: in-mem temp storage: disk budget exceeded: 1048576 bytes requested, 104857600 currently allocated, 104857600 bytes in budget

@rohany can you confirm and close the issue?

[asubiotto]

This has been fixed. The issue was that an in-memory temp store would return an OutOfMemory error when the disk budget hit a limit, instead of an OutOfDisk, which would cause us to try to spill to disk again and return "already using disk".