hg push getting worse?

[Tim Bell]

> I don't know the openjdk infrastructure, so am just guessing, but I
> suspect there are only a finite number of snapshots maintained.  The
> benefit is being able to recover :-).  AFAIK, we've only used it once
> or twice, but having the snapshots made it possible.

I was just on the hg server to shake loose a changeset in the
jdk6-gate/langtools repo.

The most obvious thing is that the push script is spending a lot of
time running '/sbin/zfs list -Ho mountpoint,name'

Running only that command by hand takes 3 mins 17 secs and produces
11485 lines of output.

During that time, truss reports hundreds of these:

brk(0x0CC6F000)                                 = 0
ioctl(3, ZFS_IOC_SNAPSHOT_LIST_NEXT, 0x08042E08) = 0
ioctl(3, ZFS_IOC_OBJSET_STATS, 0x08040F68)      = 0
ioctl(3, ZFS_IOC_SNAPSHOT_LIST_NEXT, 0x08042E08) = 0
ioctl(3, ZFS_IOC_OBJSET_STATS, 0x08040F68)      = 0
ioctl(3, ZFS_IOC_SNAPSHOT_LIST_NEXT, 0x08042E08) = 0
ioctl(3, ZFS_IOC_OBJSET_STATS, 0x08040F68)      = 0
ioctl(3, ZFS_IOC_SNAPSHOT_LIST_NEXT, 0x08042E08) = 0
ioctl(3, ZFS_IOC_OBJSET_STATS, 0x08040F68)      = 0
ioctl(3, ZFS_IOC_SNAPSHOT_LIST_NEXT, 0x08042E08) = 0
ioctl(3, ZFS_IOC_OBJSET_STATS, 0x08040F68)      = 0


ZFS snapshots are supposed to be lightweight and inexpensive.  We
still have them going back to the beginning of time on hg.ojn.

Perhaps we have accumulated enough to expose quadratic (or worse)
performance problems.  I will do some searching over on OpenSolaris.

Tim