On 01.09.2017 09:41, Andres Freund wrote:
Hi,
I previously had an early prototype of JITing [1] expression evaluation
and tuple deforming. I've since then worked a lot on this.
Here's an initial, not really pretty but functional, submission. This
supports all types of expressions, and tuples, and allows, albeit with
some drawbacks, inlining of builtin functions. Between the version at
[1] and this I'd done some work in c++, because that allowed to
experiment more with llvm, but I've now translated everything back.
Some features I'd to re-implement due to limitations of C API.
I've whacked this around quite heavily today, this likely has some new
bugs, sorry for that :(
Can you please clarify the following fragment calculating attributes
alignment:
/* compute what following columns are aligned to */
+ if (att->attlen < 0)
+ {
+ /* can't guarantee any alignment after varlen field */
+ attcuralign = -1;
+ }
+ else if (att->attnotnull && attcuralign >= 0)
+ {
+ Assert(att->attlen > 0);
+ attcuralign += att->attlen;
+ }
+ else if (att->attnotnull)
+ {
+ /*
+ * After a NOT NULL fixed-width column, alignment is
+ * guaranteed to be the minimum of the forced alignment and
+ * length. XXX
+ */
+ attcuralign = alignto + att->attlen;
+ Assert(attcuralign > 0);
+ }
+ else
+ {
+ //elog(LOG, "attnotnullreset: %d", attnum);
+ attcuralign = -1;
+ }
I wonder why in this branch (att->attnotnull && attcuralign >= 0)
we are not adding "alignto" and comment in the following branch else if
(att->attnotnull)
seems to be not related to this branch, because in this case attcuralign
is expected to be less then zero wjhich means that previous attribute is
varlen field.
--
Konstantin Knizhnik
Postgres Professional: http://www.postgrespro.com
The Russian Postgres Company
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