PHP allocating too much memory

Hi -

I'm getting the following error in php7.0.5:

Fatal Error: Allowed memory size of 536870912 bytes exhausted (tried to
allocate 140729445144864 bytes)

If it's relevant, we're using dblib+freetds.

I can't reproduce the issue deterministically; the best I can do is to
repeatedly curl an endpoint and something like 30% of the requests will
fail due to the above error.

The weirdest part about this is that PHP is somehow trying to allocate
140TB of memory.

Has anyone seen anything like this? Any insights would be appreciated.

I have!

You wouldn't, by any chance, have ODBC in the mix? The libraries you
mention seem to indicate that you might be using ODBC. There is a known
issue with mixing 32-bit and 64-bit binaries with PHP and ODBC. I don't
remember all the details, but mixing 32-bit and 64-bit binaries will see
things like NULL values as not NULL behind the scenes and do the wrong
thing whereby PHP eventually attempts to allocate a ridiculous amount of
RAM (e.g. a -1 value gets translated badly and assumes that it is the
amount of RAM to allocate). I've seen allocation requests for upwards
of 14 exabytes of RAM before - the amount varies but is always
laughable. From what I can tell, NULL values in the query results will
always trigger the problem and, even if you can guarantee that there are
no NULL values in ANY of the query results, the issue still arises at a
pretty significant rate due to bit-depth differences.

Unfortunately, due to the way ODBC itself was created and functions,
there is no easy fix within a mixed binary environment. To correctly
fix the problem, you've got to match the bit-depths of ALL of the
binaries involved - that is, either all 32-bit or all 64-bit - which is
not always possible. The alternative is to use the ugliest hack ever:
Execute a separate PHP process for running each database query that
continually retries when it fails and just live with the high failure
rates. Guess which solution I used? Fortunately, in my case, the
number of queries being run was quite limited and on a set schedule.
You might not be so lucky.

--
Thomas Hruska
CubicleSoft President

I've got great, time saving software that you will find useful.

http://cubiclesoft.com/

The weirdest part about this is that PHP is somehow trying to allocate
140TB of memory.

I've seen numbers like that a few times - always around 140TB, but the
exact number varies. I assume it's an overflow (or underflow?)
somewhere, but the exact mechanism escapes me. (It's close to 2^47,
but not very close; I've got examples logged as "low" as
140090229815192, and I think I've seen under 140 trillion.)
In hex: 00007F694C627798 - so apparently 00007F69400000000 is common to
all.
FYI: I have seen similar issues with mixed environments (32 and 64-bit)

• at this point I am surprised that you can even dlopen() both sizes (my
  OS now refuses to dlopen() 32-bit modules aka shared libraries when
  64-bit application and v.v.)

Apart from sheer curiosity of where this magic number comes from, I
wonder if there is some sanity check missing in the memory manager to
at least display a different error message...

Regards,