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db448ce5ad
Here we convert CompactAttribute.attalign from a char, which is directly derived from pg_attribute.attalign into a uint8, which stores the number of bytes to align the column's value by in the tuple. This allows tuple deformation and tuple size calculations to move away from using the inefficient att_align_nominal() macro, which manually checks each TYPALIGN_* char to translate that into the alignment bytes for the given type. Effectively, this commit changes those to TYPEALIGN calls, which are branchless and only perform some simple arithmetic with some bit-twiddling. The removed branches were often mispredicted by CPUs, especially so in real-world tables which often contain a mishmash of different types with different alignment requirements. Author: David Rowley Reviewed-by: Andres Freund, Victor Yegorov Discussion: https://postgr.es/m/CAApHDvrBztXP3yx=NKNmo3xwFAFhEdyPnvrDg3=M0RhDs+4vYw@mail.gmail.com
236 lines
7.5 KiB
C
236 lines
7.5 KiB
C
/*-------------------------------------------------------------------------
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*
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* tupmacs.h
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* Tuple macros used by both index tuples and heap tuples.
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*
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*
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* Portions Copyright (c) 1996-2024, PostgreSQL Global Development Group
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* Portions Copyright (c) 1994, Regents of the University of California
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*
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* src/include/access/tupmacs.h
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*
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*-------------------------------------------------------------------------
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*/
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#ifndef TUPMACS_H
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#define TUPMACS_H
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#include "catalog/pg_type_d.h" /* for TYPALIGN macros */
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/*
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* Check a tuple's null bitmap to determine whether the attribute is null.
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* Note that a 0 in the null bitmap indicates a null, while 1 indicates
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* non-null.
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*/
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static inline bool
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att_isnull(int ATT, const bits8 *BITS)
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{
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return !(BITS[ATT >> 3] & (1 << (ATT & 0x07)));
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}
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#ifndef FRONTEND
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/*
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* Given an attbyval and an attlen from either a Form_pg_attribute or
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* CompactAttribute and a pointer into a tuple's data area, return the
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* correct value or pointer.
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*
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* We return a Datum value in all cases. If attbyval is false, we return the
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* same pointer into the tuple data area that we're passed. Otherwise, we
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* return the correct number of bytes fetched from the data area and extended
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* to Datum form.
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*
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* On machines where Datum is 8 bytes, we support fetching 8-byte byval
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* attributes; otherwise, only 1, 2, and 4-byte values are supported.
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*
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* Note that T must already be properly aligned for this to work correctly.
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*/
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#define fetchatt(A,T) fetch_att(T, (A)->attbyval, (A)->attlen)
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/*
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* Same, but work from byval/len parameters rather than Form_pg_attribute.
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*/
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static inline Datum
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fetch_att(const void *T, bool attbyval, int attlen)
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{
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if (attbyval)
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{
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switch (attlen)
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{
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case sizeof(char):
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return CharGetDatum(*((const char *) T));
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case sizeof(int16):
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return Int16GetDatum(*((const int16 *) T));
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case sizeof(int32):
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return Int32GetDatum(*((const int32 *) T));
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#if SIZEOF_DATUM == 8
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case sizeof(Datum):
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return *((const Datum *) T);
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#endif
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default:
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elog(ERROR, "unsupported byval length: %d", attlen);
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return 0;
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}
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}
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else
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return PointerGetDatum(T);
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}
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#endif /* FRONTEND */
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/*
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* att_align_datum aligns the given offset as needed for a datum of alignment
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* requirement attalign and typlen attlen. attdatum is the Datum variable
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* we intend to pack into a tuple (it's only accessed if we are dealing with
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* a varlena type). Note that this assumes the Datum will be stored as-is;
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* callers that are intending to convert non-short varlena datums to short
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* format have to account for that themselves.
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*/
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#define att_align_datum(cur_offset, attalign, attlen, attdatum) \
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( \
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((attlen) == -1 && VARATT_IS_SHORT(DatumGetPointer(attdatum))) ? \
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(uintptr_t) (cur_offset) : \
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att_align_nominal(cur_offset, attalign) \
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)
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/*
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* Similar to att_align_datum, but accepts a number of bytes, typically from
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* CompactAttribute.attalignby to align the Datum by.
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*/
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#define att_datum_alignby(cur_offset, attalignby, attlen, attdatum) \
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( \
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((attlen) == -1 && VARATT_IS_SHORT(DatumGetPointer(attdatum))) ? \
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(uintptr_t) (cur_offset) : \
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TYPEALIGN(attalignby, cur_offset))
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/*
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* att_align_pointer performs the same calculation as att_align_datum,
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* but is used when walking a tuple. attptr is the current actual data
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* pointer; when accessing a varlena field we have to "peek" to see if we
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* are looking at a pad byte or the first byte of a 1-byte-header datum.
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* (A zero byte must be either a pad byte, or the first byte of a correctly
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* aligned 4-byte length word; in either case we can align safely. A non-zero
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* byte must be either a 1-byte length word, or the first byte of a correctly
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* aligned 4-byte length word; in either case we need not align.)
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*
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* Note: some callers pass a "char *" pointer for cur_offset. This is
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* a bit of a hack but should work all right as long as uintptr_t is the
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* correct width.
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*/
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#define att_align_pointer(cur_offset, attalign, attlen, attptr) \
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( \
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((attlen) == -1 && VARATT_NOT_PAD_BYTE(attptr)) ? \
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(uintptr_t) (cur_offset) : \
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att_align_nominal(cur_offset, attalign) \
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)
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/*
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* Similar to att_align_pointer, but accepts a number of bytes, typically from
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* CompactAttribute.attalignby to align the pointer by.
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*/
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#define att_pointer_alignby(cur_offset, attalignby, attlen, attptr) \
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( \
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((attlen) == -1 && VARATT_NOT_PAD_BYTE(attptr)) ? \
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(uintptr_t) (cur_offset) : \
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TYPEALIGN(attalignby, cur_offset))
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/*
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* att_align_nominal aligns the given offset as needed for a datum of alignment
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* requirement attalign, ignoring any consideration of packed varlena datums.
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* There are three main use cases for using this macro directly:
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* * we know that the att in question is not varlena (attlen != -1);
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* in this case it is cheaper than the above macros and just as good.
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* * we need to estimate alignment padding cost abstractly, ie without
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* reference to a real tuple. We must assume the worst case that
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* all varlenas are aligned.
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* * within arrays and multiranges, we unconditionally align varlenas (XXX this
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* should be revisited, probably).
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*
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* The attalign cases are tested in what is hopefully something like their
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* frequency of occurrence.
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*/
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#define att_align_nominal(cur_offset, attalign) \
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( \
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((attalign) == TYPALIGN_INT) ? INTALIGN(cur_offset) : \
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(((attalign) == TYPALIGN_CHAR) ? (uintptr_t) (cur_offset) : \
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(((attalign) == TYPALIGN_DOUBLE) ? DOUBLEALIGN(cur_offset) : \
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( \
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AssertMacro((attalign) == TYPALIGN_SHORT), \
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SHORTALIGN(cur_offset) \
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))) \
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)
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/*
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* Similar to att_align_nominal, but accepts a number of bytes, typically from
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* CompactAttribute.attalignby to align the offset by.
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*/
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#define att_nominal_alignby(cur_offset, attalignby) \
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TYPEALIGN(attalignby, cur_offset)
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/*
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* att_addlength_datum increments the given offset by the space needed for
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* the given Datum variable. attdatum is only accessed if we are dealing
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* with a variable-length attribute.
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*/
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#define att_addlength_datum(cur_offset, attlen, attdatum) \
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att_addlength_pointer(cur_offset, attlen, DatumGetPointer(attdatum))
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/*
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* att_addlength_pointer performs the same calculation as att_addlength_datum,
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* but is used when walking a tuple --- attptr is the pointer to the field
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* within the tuple.
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*
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* Note: some callers pass a "char *" pointer for cur_offset. This is
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* actually perfectly OK, but probably should be cleaned up along with
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* the same practice for att_align_pointer.
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*/
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#define att_addlength_pointer(cur_offset, attlen, attptr) \
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( \
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((attlen) > 0) ? \
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( \
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(cur_offset) + (attlen) \
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) \
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: (((attlen) == -1) ? \
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( \
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(cur_offset) + VARSIZE_ANY(attptr) \
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) \
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: \
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( \
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AssertMacro((attlen) == -2), \
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(cur_offset) + (strlen((char *) (attptr)) + 1) \
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)) \
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)
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#ifndef FRONTEND
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/*
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* store_att_byval is a partial inverse of fetch_att: store a given Datum
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* value into a tuple data area at the specified address. However, it only
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* handles the byval case, because in typical usage the caller needs to
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* distinguish by-val and by-ref cases anyway, and so a do-it-all function
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* wouldn't be convenient.
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*/
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static inline void
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store_att_byval(void *T, Datum newdatum, int attlen)
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{
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switch (attlen)
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{
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case sizeof(char):
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*(char *) T = DatumGetChar(newdatum);
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break;
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case sizeof(int16):
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*(int16 *) T = DatumGetInt16(newdatum);
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break;
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case sizeof(int32):
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*(int32 *) T = DatumGetInt32(newdatum);
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break;
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#if SIZEOF_DATUM == 8
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case sizeof(Datum):
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*(Datum *) T = newdatum;
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break;
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#endif
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default:
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elog(ERROR, "unsupported byval length: %d", attlen);
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}
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}
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#endif /* FRONTEND */
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#endif /* TUPMACS_H */
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