[issue1583] panic: assertion: cursor->trans->sync_lock_refs > 0 in hammer_recover_cursor

[Matthew Dillon]

:I briefly thought the low I/O figures on da1 (mirroring from da0 to da1) might
:have been a new quirk:
:
:> iostat -w1
:      tty             ad0              da0              da1             cpu
: tin tout  KB/t tps   MB/s   KB/t tps   MB/s   KB/t tps   MB/s  us ni sy in id
:   2  465  0.00    0  0.00   0.00    0  0.00   0.00    0  0.00   4  0 10  1 85
:   0   80  0.00    0  0.00  64.00  643 40.21  64.00    4  0.25  21  0 42  2 35
:   0   80  0.00    0  0.00  63.82  683 42.59  60.00    4  0.23  28  0 37  3 32
:   0   80  0.00    0  0.00  63.79  614 38.26  64.00    6  0.37  20  0 38  1 41
:
:...but it completed in appropriate time and all the data appears to be there, so
:I'm not sure if HAMMER was being smart enough to skip over what existed from a
:previous interrupted copy or what.  I don't really remember whether the
:pre-patch stats actually looked any different for the destination disk.
:
:[SATA disks on a mpt0, write caches enabled.]

    The more likely case is that the mirror stream repeated the data but
    since the target already had it there was no need to re-write it on
    the target.  In that case the only disk activity on the target will
    be accessing and comparing the meta-data.

    It tries to stage the mirroring stream so it can pick up where it
    left off but it's a bit of a hack.  If it managed to complete a
    batch then it certainly will pick up after the completion and not
    resend the whole batch.  I need to redo the code to actually
    calculate the batch size and split things up based on that instead
    of splitting things up based on B-Tree key ranges.

    This applies to initial mirroring only, of course.  Once the initial
    copy is finished all later mirroring runs will be incremental.

					-Matt
					Matthew Dillon 
					<dillon at backplane.com>