While discussing comment improvements (see next commit) by Justin
Pryzby, Tom complained about a few details of the logic to infer the
length of the NULL bitmap when building the JITed tuple deforming
function. That bitmap allows to avoid checking the tuple header's
natts, a check which often causes a pipeline stall
Improvements:
a) As long as missing columns aren't taken into account, we can
continue to infer the length of the NULL bitmap from NOT NULL
columns following it. Previously we stopped at the first missing
column. It's unlikely to matter much in practice, but the
alternative would have been to document why we stop.
b) For robustness reasons it seems better to also check against
attisdropped - RemoveAttributeById() sets attnotnull to false, but
an additional check is trivial.
c) Improve related comments
Discussion: https://postgr.es/m/20637.1555957068@sss.pgh.pa.us
Backpatch: -
The function generated to perform JIT compiled tuple deforming failed
when HeapTupleHeader's t_hoff was bigger than a signed int8. I'd
failed to realize that LLVM's getelementptr would treat an int8 index
argument as signed, rather than unsigned. That means that a hoff
larger than 127 would result in a negative offset being applied. Fix
that by widening the index to 32bit.
Add a testcase with a wide table. Don't drop it, as it seems useful to
verify other tools deal properly with wide tables.
Thanks to Justin Pryzby for both reporting a bug and then reducing it
to a reproducible testcase!
Reported-By: Justin Pryzby
Author: Andres Freund
Discussion: https://postgr.es/m/20181115223959.GB10913@telsasoft.com
Backpatch: 11, just as jit compilation was
This commit completes the work prepared in 1a0586de36, splitting the
old TupleTableSlot implementation (which could store buffer, heap,
minimal and virtual slots) into four different slot types. As
described in the aforementioned commit, this is done with the goal of
making tuple table slots extensible, to allow for pluggable table
access methods.
To achieve runtime extensibility for TupleTableSlots, operations on
slots that can differ between types of slots are performed using the
TupleTableSlotOps struct provided at slot creation time. That
includes information from the size of TupleTableSlot struct to be
allocated, initialization, deforming etc. See the struct's definition
for more detailed information about callbacks TupleTableSlotOps.
I decided to rename TTSOpsBufferTuple to TTSOpsBufferHeapTuple and
ExecCopySlotTuple to ExecCopySlotHeapTuple, as that seems more
consistent with other naming introduced in recent patches.
There's plenty optimization potential in the slot implementation, but
according to benchmarking the state after this commit has similar
performance characteristics to before this set of changes, which seems
sufficient.
There's a few changes in execReplication.c that currently need to poke
through the slot abstraction, that'll be repaired once the pluggable
storage patchset provides the necessary infrastructure.
Author: Andres Freund and Ashutosh Bapat, with changes by Amit Khandekar
Discussion: https://postgr.es/m/20181105210039.hh4vvi4vwoq5ba2q@alap3.anarazel.de
Virtual tuple table slots never need tuple deforming. Therefore, if we
know at expression compilation time, that a certain slot will always
be virtual, there's no need to create a tuple deforming routine for
it.
Author: Andres Freund
Discussion: https://postgr.es/m/20181105210039.hh4vvi4vwoq5ba2q@alap3.anarazel.de
There's several reasons for this change:
1) It reduces the total size of TupleTableSlot / reduces alignment
padding, making the commonly accessed members fit into a single
cacheline (but we currently do not force proper alignment, so
that's not yet guaranteed to be helpful)
2) Combining the booleans into a flag allows to combine read/writes
from memory.
3) With the upcoming slot abstraction changes, it allows to have core
and extended flags, in a memory efficient way.
Author: Ashutosh Bapat and Andres Freund
Discussion: https://postgr.es/m/20180220224318.gw4oe5jadhpmcdnm@alap3.anarazel.de
Previously it was an int / 4 bytes. The maximum number of attributes
in a tuple is restricted by the maximum value Var->varattno, which is
an AttrNumber/int16. Hence use the same data type for
TupleTableSlot->tts_nvalid.
Author: Ashutosh Bapat
Discussion: https://postgr.es/m/20180220224318.gw4oe5jadhpmcdnm@alap3.anarazel.de
Instead using memset to set tts_isnull, call the new
slot_getmissingattrs().
Also fix a bug (= instead of >=) in the code generation. Normally = is
correct, but when repeatedly deforming fields not in a
tuple (e.g. deform up to natts + 1 and then natts + 2) >= is needed.
Discussion: https://postgr.es/m/20180328010053.i2qvsuuusst4lgmc@alap3.anarazel.de
Performing JIT compilation for deforming gains performance benefits
over unJITed deforming from compile-time knowledge of the tuple
descriptor. Fixed column widths, NOT NULLness, etc can be taken
advantage of.
Right now the JITed deforming is only used when deforming tuples as
part of expression evaluation (and obviously only if the descriptor is
known). It's likely to be beneficial in other cases, too.
By default tuple deforming is JITed whenever an expression is JIT
compiled. There's a separate boolean GUC controlling it, but that's
expected to be primarily useful for development and benchmarking.
Docs will follow in a later commit containing docs for the whole JIT
feature.
Author: Andres Freund
Discussion: https://postgr.es/m/20170901064131.tazjxwus3k2w3ybh@alap3.anarazel.de