Attempting to escape large, untrusted strings cause stack
overflows (easier under Ruby 1.9 using pthreads) leading to
SystemStackError on small overflows and segmentation faults on
large overflows. Instead of allocating on the stack, we'll
allocate a string buffer from the heap.
This has the unfortunate effect of reducing escape performance
for common cases, but in my experience SQL escaping isn't much
of a bottleneck.
For reference, Ruby 1.9.2-p0 with pthreads gets a stack size of
512K and the default process stack size is 8MB on both x86 and
x86_64 Linux.
The MySQL client libraries normally retry system calls when
interrupted by signals. The lone exception I've found is in the
(infrequent) connection setup where it'll propagate the
connect(2) syscall error all the way back up to the caller.
Fortunately inspection of the MySQL client library reveals it
properly preserves the global "errno" variable even with
debugging enabled.
Note that the net.last_errno member does NOT correspond to the
system "errno".
This reverts the single-threaded select() optimization from
commits 9a63a587c0 and
0190457dbd.
Under Ruby 1.9, the reverted optimization caused signal handlers
to be delayed until the socket became readable.
Under Ruby 1.8, matters are worse as receiving a signal during
select() causes Errno::EINTR to be raised.
There is now a (somewhat fragile) spec for testing signal
handling during a "SELECT sleep(2)" query.
Furthermore, the performance difference I measured on
benchmark/thread_alone.rb was negligible (over 1000 iterations)
between the two:
Ruby 1.8.7-p249
Rehearsal ----------------------------------------------------
select 0.040000 0.020000 0.060000 ( 0.119448)
rb_thread_select 0.050000 0.020000 0.070000 ( 0.132091)
------------------------------------------- total: 0.130000sec
user system total real
select 0.030000 0.030000 0.060000 ( 0.116471)
rb_thread_select 0.050000 0.020000 0.070000 ( 0.119874)
Ruby 1.9.2-p0
Rehearsal ----------------------------------------------------
select 0.050000 0.030000 0.080000 ( 0.134208)
rb_thread_select 0.080000 0.000000 0.080000 ( 0.141316)
------------------------------------------- total: 0.160000sec
user system total real
select 0.050000 0.020000 0.070000 ( 0.123325)
rb_thread_select 0.060000 0.010000 0.070000 ( 0.124075)
Benchmarks were performed on an _empty_ mysql2_test table to
maximize the relative time for the select(2)-related code path
(vs reading data). The test was run on Debian Lenny, x86_64 and
a stock 2.6.35.2 Linux kernel. Hardware was a Core2 Duo @
1.6GHz with the performance CPU governor while on AC power
to eliminate CPU speed fluctuations during the test.
1) let mysql_init/mysql_close take care of any/all allocation, thread state and freeing
2) for faster access to the encoding and active state variables for the connection
Brian Lopez
Eric Wong
Luis Lavena
Aaron Patterson
Lourens Naudé