Add support of numeric error suppression to jsonpath as it's required by
standard. This commit doesn't use PG_TRY()/PG_CATCH() in order to implement
that. Instead, it provides internal versions of numeric functions used, which
support error suppression.
Discussion: https://postgr.es/m/fcc6fc6a-b497-f39a-923d-aa34d0c588e8%402ndQuadrant.com
Author: Alexander Korotkov, Nikita Glukhov
Reviewed-by: Tomas Vondra
The SQL:2016 standard adds support for the hyperbolic functions
sinh(), cosh(), and tanh(). POSIX has long required libm to
provide those functions as well as their inverses asinh(),
acosh(), atanh(). Hence, let's just expose the libm functions
to the SQL level. As with the trig functions, we only implement
versions for float8, not numeric.
For the moment, we'll assume that all platforms actually do have
these functions; if experience teaches otherwise, some autoconf
effort may be needed.
SQL:2016 also adds support for base-10 logarithm, but with the
function name log10(), whereas the name we've long used is log().
Add aliases named log10() for the float8 and numeric versions.
Lætitia Avrot
Discussion: https://postgr.es/m/CAB_COdguG22LO=rnxDQ2DW1uzv8aQoUzyDQNJjrR4k00XSgm5w@mail.gmail.com
Previously, floating-point output was done by rounding to a specific
decimal precision; by default, to 6 or 15 decimal digits (losing
information) or as requested using extra_float_digits. Drivers that
wanted exact float values, and applications like pg_dump that must
preserve values exactly, set extra_float_digits=3 (or sometimes 2 for
historical reasons, though this isn't enough for float4).
Unfortunately, decimal rounded output is slow enough to become a
noticable bottleneck when dealing with large result sets or COPY of
large tables when many floating-point values are involved.
Floating-point output can be done much faster when the output is not
rounded to a specific decimal length, but rather is chosen as the
shortest decimal representation that is closer to the original float
value than to any other value representable in the same precision. The
recently published Ryu algorithm by Ulf Adams is both relatively
simple and remarkably fast.
Accordingly, change float4out/float8out to output shortest decimal
representations if extra_float_digits is greater than 0, and make that
the new default. Applications that need rounded output can set
extra_float_digits back to 0 or below, and take the resulting
performance hit.
We make one concession to portability for systems with buggy
floating-point input: we do not output decimal values that fall
exactly halfway between adjacent representable binary values (which
would rely on the reader doing round-to-nearest-even correctly). This
is known to be a problem at least for VS2013 on Windows.
Our version of the Ryu code originates from
https://github.com/ulfjack/ryu/ at commit c9c3fb1979, but with the
following (significant) modifications:
- Output format is changed to use fixed-point notation for small
exponents, as printf would, and also to use lowercase 'e', a
minimum of 2 exponent digits, and a mandatory sign on the exponent,
to keep the formatting as close as possible to previous output.
- The output of exact midpoint values is disabled as noted above.
- The integer fast-path code is changed somewhat (since we have
fixed-point output and the upstream did not).
- Our project style has been largely applied to the code with the
exception of C99 declaration-after-statement, which has been
retained as an exception to our present policy.
- Most of upstream's debugging and conditionals are removed, and we
use our own configure tests to determine things like uint128
availability.
Changing the float output format obviously affects a number of
regression tests. This patch uses an explicit setting of
extra_float_digits=0 for test output that is not expected to be
exactly reproducible (e.g. due to numerical instability or differing
algorithms for transcendental functions).
Conversions from floats to numeric are unchanged by this patch. These
may appear in index expressions and it is not yet clear whether any
change should be made, so that can be left for another day.
This patch assumes that the only supported floating point format is
now IEEE format, and the documentation is updated to reflect that.
Code by me, adapting the work of Ulf Adams and other contributors.
References:
https://dl.acm.org/citation.cfm?id=3192369
Reviewed-by: Tom Lane, Andres Freund, Donald Dong
Discussion: https://postgr.es/m/87r2el1bx6.fsf@news-spur.riddles.org.uk
Using strtod() creates a double-rounding problem; the input decimal
value is first rounded to the nearest double; rounding that to the
nearest float may then give an incorrect result.
An example is that 7.038531e-26 when input via strtod and then rounded
to float4 gives 0xAE43FEp-107 instead of the correct 0xAE43FDp-107.
Values output by earlier PG versions with extra_float_digits=3 should
all be read in with the same values as previously. However, values
supplied by other software using shortest representations could be
mis-read.
On platforms that lack a strtof() entirely, we fall back to the old
incorrect rounding behavior. (As strtof() is required by C99, such
platforms are considered of primarily historical interest.) On VS2013,
some workarounds are used to get correct error handling.
The regression tests now test for the correct input values, so
platforms that lack strtof() will need resultmap entries. An entry for
HP-UX 10 is included (more may be needed).
Reviewed-By: Tom Lane
Discussion: https://postgr.es/m/871s5emitx.fsf@news-spur.riddles.org.uk
Discussion: https://postgr.es/m/87d0owlqpv.fsf@news-spur.riddles.org.uk
This removes a portion of infrastructure introduced by fe0a0b5 to allow
compilation of Postgres in environments where no strong random source is
available, meaning that there is no linking to OpenSSL and no
/dev/urandom (Windows having its own CryptoAPI). No systems shipped
this century lack /dev/urandom, and the buildfarm is actually not
testing this switch at all, so just remove it. This simplifies
particularly some backend code which included a fallback implementation
using shared memory, and removes a set of alternate regression output
files from pgcrypto.
Author: Michael Paquier
Reviewed-by: Tom Lane
Discussion: https://postgr.es/m/20181230063219.GG608@paquier.xyz
Previously, the SQL random() function depended on libc's random(3),
and setseed() invoked srandom(3). This results in interference between
these functions and backend-internal uses of random(3). We'd never paid
too much mind to that, but in the wake of commit 88bdbd3f7 which added
log_statement_sample_rate, the interference arguably has a security
consequence: if log_statement_sample_rate is active then an unprivileged
user could probably control which if any of his SQL commands get logged,
by issuing setseed() at the right times. That seems bad.
To fix this reliably, we need random() and setseed() to use their own
private random state variable. Standard random(3) isn't amenable to such
usage, so let's switch to pg_erand48(). It's hard to say whether that's
more or less "random" than any particular platform's version of random(3),
but it does have a wider seed value and a longer period than are required
by POSIX, so we can hope that this isn't a big downgrade. Also, we should
now have uniform behavior of random() across platforms, which is worth
something.
While at it, upgrade the per-process seed initialization method to use
pg_strong_random() if available, greatly reducing the predictability
of the initial seed value. (I'll separately do something similar for
the internal uses of random().)
In addition to forestalling the possible security problem, this has a
benefit in the other direction, which is that we can now document
setseed() as guaranteeing a reproducible sequence of random() values.
Previously, because of the possibility of internal calls of random(3),
we could not promise any such thing.
Discussion: https://postgr.es/m/3859.1545849900@sss.pgh.pa.us
ftoi4 and its sibling coercion functions did their overflow checks in
a way that looked superficially plausible, but actually depended on an
assumption that the MIN and MAX comparison constants can be represented
exactly in the float4 or float8 domain. That fails in ftoi4, ftoi8,
and dtoi8, resulting in a possibility that values near the MAX limit will
be wrongly converted (to negative values) when they need to be rejected.
Also, because we compared before rounding off the fractional part,
the other three functions threw errors for values that really ought
to get rounded to the min or max integer value.
Fix by doing rint() first (requiring an assumption that it handles
NaN and Inf correctly; but dtoi8 and ftoi8 were assuming that already),
and by comparing to values that should coerce to float exactly, namely
INTxx_MIN and -INTxx_MIN. Also remove some random cosmetic discrepancies
between these six functions.
Per bug #15519 from Victor Petrovykh. This should get back-patched,
but first let's see what the buildfarm thinks of it --- I'm not too
sure about portability of some of the regression test cases.
Patch by me; thanks to Andrew Gierth for analysis and discussion.
Discussion: https://postgr.es/m/15519-4fc785b483201ff1@postgresql.org
Up to now, float4out/float8out handled NaN and Infinity cases explicitly,
and invoked psprintf only for ordinary float values. This was done because
platform implementations of snprintf produce varying representations of
these special cases. But now that we use snprintf.c always, it's better
to give it the responsibility to produce a uniform representation of
these cases, so that we have uniformity across the board not only in
float4out/float8out. Hence, move that work into fmtfloat().
Also, teach fmtfloat() to recognize IEEE minus zero and handle it
correctly. The previous coding worked only accidentally, and would
fail for e.g. "%+f" format (it'd print "+-0.00000"). Now that we're
using snprintf.c everywhere, it's not acceptable for it to do weird
things in corner cases. (This incidentally avoids a portability
problem we've seen on some really ancient platforms, that native
sprintf does the wrong thing with minus zero.)
Also, introduce a new entry point in snprintf.c to allow float[48]out
to bypass the work of interpreting a well-known format spec, as well
as bypassing the overhead of the psprintf layer. I modeled this API
loosely on strfromd(). In my testing, this brings float[48]out back
to approximately the same speed they had when using native snprintf,
fixing one of the main performance issues caused by using snprintf.c.
(There is some talk of more aggressive work to improve the speed of
floating-point output conversion, but these changes seem to provide
a better starting point for such work anyway.)
Getting rid of the previous ad-hoc hack for Infinity/NaN in fmtfloat()
allows removing <ctype.h> from snprintf.c's #includes. I also removed
a few other #includes that I think are historical, though the buildfarm
may expose that as wrong.
Discussion: https://postgr.es/m/13178.1538794717@sss.pgh.pa.us
When computing statistical aggregates like variance, the common
schoolbook algorithm which computes the sum of the squares of the
values and subtracts the square of the mean can lead to a large loss
of precision when using floating point arithmetic, because the
difference between the two terms is often very small relative to the
terms themselves.
To avoid this, re-work these aggregates to use the Youngs-Cramer
algorithm, which is a proven, numerically stable algorithm that
directly aggregates the sum of the squares of the differences of the
values from the mean in a single pass over the data.
While at it, improve the test coverage to test the aggregate combine
functions used during parallel aggregation.
Per report and suggested algorithm from Erich Schubert.
Patch by me, reviewed by Madeleine Thompson.
Discussion: https://postgr.es/m/153313051300.1397.9594490737341194671@wrigleys.postgresql.org
Some data types under adt/ have separate header files, but most simple
ones do not, and their public functions are defined in builtins.h. As
the patches improving geometric types will require making additional
functions public, this seems like a good opportunity to create a header
for floats types.
Commit 1acf757255 made _cmp functions public to solve NaN issues locally
for GiST indexes. This patch reworks it in favour of a more widely
applicable API. The API uses inline functions, as they are easier to
use compared to macros, and avoid double-evaluation hazards.
Author: Emre Hasegeli
Reviewed-by: Kyotaro Horiguchi
Discussion: https://www.postgresql.org/message-id/CAE2gYzxF7-5djV6-cEvqQu-fNsnt%3DEqbOURx7ZDg%2BVv6ZMTWbg%40mail.gmail.com
In commit 8b29e88cd, I'd dithered about whether to make
in_range_float4_float8 be a standalone copy of the float in-range logic
or have it punt to in_range_float8_float8. I went with the latter, which
saves code space though at the cost of performance and readability.
However, it emerges that this tickles a compiler or hardware bug on
buildfarm member opossum. Test results from commit 55e0e4581 show
conclusively that widening a float4 NaN to float8 produces Inf, not NaN,
on that machine; which accounts perfectly for the window RANGE test
failures it's been showing. We can dodge this problem by making
in_range_float4_float8 be an independent function, so that it checks
for NaN inputs before widening them.
Ordinarily I'd not be very excited about working around such obviously
broken functionality; but given that this was a judgment call to begin
with, I don't mind reversing it.
Buildfarm results show that the modern POSIX rule that 1 ^ NaN = 1 is not
honored on *BSD until relatively recently, and really old platforms don't
believe that NaN ^ 0 = 1 either. (This is unsurprising, perhaps, since
SUSv2 doesn't require either behavior.) In hopes of getting to platform
independent behavior, let's deal with all the NaN-input cases explicitly
in dpow().
Note that numeric_power() doesn't know either of these special cases.
But since that behavior is platform-independent, I think it should be
addressed separately, and probably not back-patched.
Discussion: https://postgr.es/m/75DB81BEEA95B445AE6D576A0A5C9E936A73E741@BPXM05GP.gisp.nec.co.jp
Per spec, the result of power() should be NaN if either input is NaN.
It appears that on some versions of Windows, the libc function does
return NaN, but it also sets errno = EDOM, confusing our code that
attempts to work around shortcomings of other platforms. Hence, add
guard tests to avoid substituting a wrong result for the right one.
It's been like this for a long time (and the odd behavior only appears
in older MSVC releases, too) so back-patch to all supported branches.
Dang Minh Huong, reviewed by David Rowley
Discussion: https://postgr.es/m/75DB81BEEA95B445AE6D576A0A5C9E936A73E741@BPXM05GP.gisp.nec.co.jp
Fix the warnings created by the compiler warning options
-Wformat-overflow=2 -Wformat-truncation=2, supported since GCC 7. This
is a more aggressive variant of the fixes in
6275f5d28a, which GCC 7 warned about by
default.
The issues are all harmless, but some dubious coding patterns are
cleaned up.
One issue that is of external interest is that BGW_MAXLEN is increased
from 64 to 96. Apparently, the old value would cause the bgw_name of
logical replication workers to be truncated in some circumstances.
But this doesn't actually add those warning options. It appears that
the warnings depend a bit on compilation and optimization options, so it
would be annoying to have to keep up with that. This is more of a
once-in-a-while cleanup.
Reviewed-by: Michael Paquier <michael@paquier.xyz>
Commit 0a459cec9 left this for later, but since time's running out,
I went ahead and took care of it. There are more data types that
somebody might someday want RANGE support for, but this is enough
to satisfy all expectations of the SQL standard, which just says that
"numeric, datetime, and interval" types should have RANGE support.
A previous commit added inline functions that provide fast(er) and
correct overflow checks for signed integer math. Use them in a
significant portion of backend code. There's more to touch in both
backend and frontend code, but these were the easily identifiable
cases.
The old overflow checks are noticeable in integer heavy workloads.
A secondary benefit is that getting rid of overflow checks that rely
on signed integer overflow wrapping around, will allow us to get rid
of -fwrapv in the future. Which in turn slows down other code.
Author: Andres Freund
Discussion: https://postgr.es/m/20171024103954.ztmatprlglz3rwke@alap3.anarazel.de
Don't move parenthesized lines to the left, even if that means they
flow past the right margin.
By default, BSD indent lines up statement continuation lines that are
within parentheses so that they start just to the right of the preceding
left parenthesis. However, traditionally, if that resulted in the
continuation line extending to the right of the desired right margin,
then indent would push it left just far enough to not overrun the margin,
if it could do so without making the continuation line start to the left of
the current statement indent. That makes for a weird mix of indentations
unless one has been completely rigid about never violating the 80-column
limit.
This behavior has been pretty universally panned by Postgres developers.
Hence, disable it with indent's new -lpl switch, so that parenthesized
lines are always lined up with the preceding left paren.
This patch is much less interesting than the first round of indent
changes, but also bulkier, so I thought it best to separate the effects.
Discussion: https://postgr.es/m/E1dAmxK-0006EE-1r@gemulon.postgresql.org
Discussion: https://postgr.es/m/30527.1495162840@sss.pgh.pa.us
Change pg_bsd_indent to follow upstream rules for placement of comments
to the right of code, and remove pgindent hack that caused comments
following #endif to not obey the general rule.
Commit e3860ffa4d wasn't actually using
the published version of pg_bsd_indent, but a hacked-up version that
tried to minimize the amount of movement of comments to the right of
code. The situation of interest is where such a comment has to be
moved to the right of its default placement at column 33 because there's
code there. BSD indent has always moved right in units of tab stops
in such cases --- but in the previous incarnation, indent was working
in 8-space tab stops, while now it knows we use 4-space tabs. So the
net result is that in about half the cases, such comments are placed
one tab stop left of before. This is better all around: it leaves
more room on the line for comment text, and it means that in such
cases the comment uniformly starts at the next 4-space tab stop after
the code, rather than sometimes one and sometimes two tabs after.
Also, ensure that comments following #endif are indented the same
as comments following other preprocessor commands such as #else.
That inconsistency turns out to have been self-inflicted damage
from a poorly-thought-through post-indent "fixup" in pgindent.
This patch is much less interesting than the first round of indent
changes, but also bulkier, so I thought it best to separate the effects.
Discussion: https://postgr.es/m/E1dAmxK-0006EE-1r@gemulon.postgresql.org
Discussion: https://postgr.es/m/30527.1495162840@sss.pgh.pa.us
This avoids additional translatable strings for each distinct type, as
well as making our quoting style around type names more consistent
(namely, that we don't quote type names). This continues what started
as f402b99501.
Discussion: https://postgr.es/m/20160401170642.GA57509@alvherre.pgsql
GiST index build could go into an infinite loop when presented with boxes
(or points, circles or polygons) containing NaN component values. This
happened essentially because the code assumed that x == x is true for any
"double" value x; but it's not true for NaNs. The looping behavior was not
the only problem though: we also attempted to sort the items using simple
double comparisons. Since NaNs violate the trichotomy law, qsort could
(in principle at least) get arbitrarily confused and mess up the sorting of
ordinary values as well as NaNs. And we based splitting choices on box size
calculations that could produce NaNs, again resulting in undesirable
behavior.
To fix, replace all comparisons of doubles in this logic with
float8_cmp_internal, which is NaN-aware and is careful to sort NaNs
consistently, higher than any non-NaN. Also rearrange the box size
calculation to not produce NaNs; instead it should produce an infinity
for a box with NaN on one side and not-NaN on the other.
I don't by any means claim that this solves all problems with NaNs in
geometric values, but it should at least make GiST index insertion work
reliably with such data. It's likely that the index search side of things
still needs some work, and probably regular geometric operations too.
But with this patch we're laying down a convention for how such cases
ought to behave.
Per bug #14238 from Guang-Dih Lei. Back-patch to 9.2; the code used before
commit 7f3bd86843 is quite different and doesn't lock up on my simple
test case, nor on the submitter's dataset.
Report: <20160708151747.1426.60150@wrigleys.postgresql.org>
Discussion: <28685.1468246504@sss.pgh.pa.us>
The true explanation for Peter Eisentraut's report of inexact asind results
seems to be that (a) he's compiling into x87 instruction set, which uses
wider-than-double float registers, plus (b) the library function asin() on
his platform returns a result that is wider than double and is not rounded
to double width. To fix, we have to force the function's result to be
rounded comparably to what happened to the scaling constant asin_0_5.
Experimentation suggests that storing it into a volatile local variable is
the least ugly way of making that happen. Although only asin() is known to
exhibit an observable inexact result, we'd better do this in all the places
where we're hoping to get an exact result by scaling.
Commit 65abaab547 tried to prevent the scaling constants used in
the degree-based trig functions from being precomputed at compile time,
because some compilers do that with functions that don't yield results
identical-to-the-last-bit to what you get at runtime. A report from
Peter Eisentraut suggests that some recent compilers are smart enough
to see through that trick, though. Instead, let's put the inputs to
these calculations into non-const global variables, which should be a
more reliable way of convincing the compiler that it can't assume that
they are compile-time constants. (If we really get desperate, we could
mark these variables "volatile", but I do not believe we should have to.)
This allows parallel aggregation to use them. It may seem surprising
that we use float8_combine for both float4_accum and float8_accum
transition functions, but that's because those functions differ only
in the type of the non-transition-state argument.
Haribabu Kommi, reviewed by David Rowley and Tomas Vondra
Formerly, the geometric I/O routines such as box_in and point_out relied
directly on strtod() and sprintf() for conversion of the float8 component
values of their data types. However, the behavior of those functions is
pretty platform-dependent, especially for edge-case values such as
infinities and NaNs. This was exposed by commit acdf2a8b37, which
added test cases involving boxes with infinity endpoints, and immediately
failed on Windows and AIX buildfarm members. We solved these problems
years ago in the main float8in and float8out functions, so let's fix it
by making the geometric types use that code instead of depending directly
on the platform-supplied functions.
To do this, refactor the float8in code so that it can be used to parse
just part of a string, and as a convenience make the guts of float8out
usable without going through DirectFunctionCall.
While at it, get rid of geo_ops.c's fairly shaky assumptions about the
maximum output string length for a double, by having it build results in
StringInfo buffers instead of fixed-length strings.
In passing, convert all the "invalid input syntax for type foo" messages
in this area of the code into "invalid input syntax for type %s" to reduce
the number of distinct translatable strings, per recent discussion.
We would have needed a fair number of the latter anyway for code-sharing
reasons, so we might as well just go whole hog.
Note: this patch is by no means intended to guarantee that the geometric
types uniformly behave sanely for infinity or NaN component values.
But any bugs we have in that line were there all along, they were just
harder to reach in a platform-independent way.
Buildfarm member cockatiel is still saying that cosd(60) isn't 0.5.
What seems likely is that the subexpression (1.0 - cos(x)) isn't being
rounded to double width before more arithmetic is done on it, so force
that by storing it into a variable.
The last round didn't do it. Per Noah Misch, the problem on at least
some machines is that the compiler pre-evaluates trig functions having
constant arguments using code slightly different from what will be used
at runtime. Therefore, we must prevent the compiler from seeing constant
arguments to any of the libm trig functions used in this code.
The method used here might still fail if init_degree_constants() gets
inlined into the call sites. That probably won't happen given the large
number of call sites; but if it does, we could probably fix it by making
init_degree_constants() non-static. I'll avoid that till proven
necessary, though.
The buildfarm isn't very happy with the results of commit e1bd684a34.
To try to get the expected exact results everywhere:
* Replace M_PI / 180 subexpressions with a precomputed constant, so that
the compiler can't decide to rearrange that division with an adjacent
operation. Hopefully this will fix failures to get exactly 0.5 from
sind(30) and cosd(60).
* Add scaling to ensure that tand(45) and cotd(45) give exactly 1; there
was nothing particularly guaranteeing that before.
* Replace minus zero by zero when tand() or cotd() would output that;
many machines did so for tand(180) and cotd(270), but not all. We could
alternatively deem both results valid, but that doesn't seem likely to
be what users will want.
The implementations go to some lengths to deliver exact results for values
where an exact result can be expected, such as sind(30) = 0.5 exactly.
Dean Rasheed, reviewed by Michael Paquier
Ensure that the trig functions return NaN for NaN input regardless of what
the underlying C library functions might do. Also ensure that an error
is thrown for Inf (or otherwise out-of-range) input, except for atan/atan2
which should accept it.
All these behaviors should now conform to the POSIX spec; previously, all
our popular platforms deviated from that in one case or another.
The main remaining platform dependency here is whether the C library might
choose to throw a domain error for sin/cos/tan inputs that are large but
less than infinity. (Doing so is not unreasonable, since once a single
unit-in-the-last-place exceeds PI, there can be no significance at all in
the result; however there doesn't seem to be any suggestion in POSIX that
such an error is allowed.) We will report such errors if they are reported
via "errno", but not if they are reported via "fetestexcept" which is the
other mechanism sanctioned by POSIX. Some preliminary experiments with
fetestexcept indicated that it might also report errors we could do
without, such as complaining about underflow at an unreasonably large
threshold. So let's skip that complexity for now.
Dean Rasheed, reviewed by Michael Paquier
Development of IRIX has been discontinued, and support is scheduled
to end in December of 2013. Therefore, there will be no supported
versions of this operating system by the time PostgreSQL 9.4 is
released. Furthermore, we have no maintainer for this platform.
The C99 and POSIX standards require strtod() to accept all these spellings
(case-insensitively): "inf", "+inf", "-inf", "infinity", "+infinity",
"-infinity". However, pre-C99 systems might accept only some or none of
these, and apparently Windows still doesn't accept "inf". To avoid
surprising cross-platform behavioral differences, manually check for each
of these spellings if strtod() fails. We were previously handling just
"infinity" and "-infinity" that way, but since C99 is most of the world
now, it seems likely that applications are expecting all these spellings
to work.
Per bug #8355 from Basil Peace. It turns out this fix won't actually
resolve his problem, because Python isn't being this careful; but that
doesn't mean we shouldn't be.
In most cases, these were just references to the SQL standard in
general. In a few cases, a contrast was made between SQL92 and later
standards -- those have been kept unchanged.
On some platforms, strtod() reports ERANGE for a denormalized value (ie,
one that can be represented as distinct from zero, but is too small to have
full precision). On others, it doesn't. It seems better to try to accept
these values consistently, so add a test to see if the result value
indicates a true out-of-range condition. This should be okay per Single
Unix Spec. On machines where the underlying math isn't IEEE standard, the
behavior for such small numbers may not be very consistent, but then it
wouldn't be anyway.
Marti Raudsepp, after a proposal by Jeroen Vermeulen
This patch creates an API whereby a btree index opclass can optionally
provide non-SQL-callable support functions for sorting. In the initial
patch, we only use this to provide a directly-callable comparator function,
which can be invoked with a bit less overhead than the traditional
SQL-callable comparator. While that should be of value in itself, the real
reason for doing this is to provide a datatype-extensible framework for
more aggressive optimizations, as in Peter Geoghegan's recent work.
Robert Haas and Tom Lane
Amit Kapila