diff options
Diffstat (limited to 'src/include')
| -rw-r--r-- | src/include/c.h | 34 | ||||
| -rw-r--r-- | src/include/pg_config_manual.h | 6 | ||||
| -rw-r--r-- | src/include/storage/fd.h | 5 |
3 files changed, 35 insertions, 10 deletions
diff --git a/src/include/c.h b/src/include/c.h index 5fe7a97ff03..f69d739be57 100644 --- a/src/include/c.h +++ b/src/include/c.h @@ -1119,14 +1119,11 @@ extern void ExceptionalCondition(const char *conditionName, /* * Use this, not "char buf[BLCKSZ]", to declare a field or local variable - * holding a page buffer, if that page might be accessed as a page and not - * just a string of bytes. Otherwise the variable might be under-aligned, - * causing problems on alignment-picky hardware. (In some places, we use - * this to declare buffers even though we only pass them to read() and - * write(), because copying to/from aligned buffers is usually faster than - * using unaligned buffers.) We include both "double" and "int64" in the - * union to ensure that the compiler knows the value must be MAXALIGN'ed - * (cf. configure's computation of MAXIMUM_ALIGNOF). + * holding a page buffer, if that page might be accessed as a page. Otherwise + * the variable might be under-aligned, causing problems on alignment-picky + * hardware. We include both "double" and "int64" in the union to ensure that + * the compiler knows the value must be MAXALIGN'ed (cf. configure's + * computation of MAXIMUM_ALIGNOF). */ typedef union PGAlignedBlock { @@ -1135,9 +1132,30 @@ typedef union PGAlignedBlock int64 force_align_i64; } PGAlignedBlock; +/* + * Use this to declare a field or local variable holding a page buffer, if that + * page might be accessed as a page or passed to an SMgr I/O function. If + * allocating using the MemoryContext API, the aligned allocation functions + * should be used with PG_IO_ALIGN_SIZE. This alignment may be more efficient + * for I/O in general, but may be strictly required on some platforms when + * using direct I/O. + */ +typedef union PGIOAlignedBlock +{ +#ifdef pg_attribute_aligned + pg_attribute_aligned(PG_IO_ALIGN_SIZE) +#endif + char data[BLCKSZ]; + double force_align_d; + int64 force_align_i64; +} PGIOAlignedBlock; + /* Same, but for an XLOG_BLCKSZ-sized buffer */ typedef union PGAlignedXLogBlock { +#ifdef pg_attribute_aligned + pg_attribute_aligned(PG_IO_ALIGN_SIZE) +#endif char data[XLOG_BLCKSZ]; double force_align_d; int64 force_align_i64; diff --git a/src/include/pg_config_manual.h b/src/include/pg_config_manual.h index b586ee269a0..33ec6102c15 100644 --- a/src/include/pg_config_manual.h +++ b/src/include/pg_config_manual.h @@ -228,6 +228,12 @@ #define PG_CACHE_LINE_SIZE 128 /* + * Assumed alignment requirement for direct I/O. 4K corresponds to common + * sector and memory page size. + */ +#define PG_IO_ALIGN_SIZE 4096 + +/* *------------------------------------------------------------------------ * The following symbols are for enabling debugging code, not for * controlling user-visible features or resource limits. diff --git a/src/include/storage/fd.h b/src/include/storage/fd.h index daceafd4732..faac4914fea 100644 --- a/src/include/storage/fd.h +++ b/src/include/storage/fd.h @@ -82,9 +82,10 @@ extern PGDLLIMPORT int max_safe_fds; * to the appropriate Windows flag in src/port/open.c. We simulate it with * fcntl(F_NOCACHE) on macOS inside fd.c's open() wrapper. We use the name * PG_O_DIRECT rather than defining O_DIRECT in that case (probably not a good - * idea on a Unix). + * idea on a Unix). We can only use it if the compiler will correctly align + * PGIOAlignedBlock for us, though. */ -#if defined(O_DIRECT) +#if defined(O_DIRECT) && defined(pg_attribute_aligned) #define PG_O_DIRECT O_DIRECT #elif defined(F_NOCACHE) #define PG_O_DIRECT 0x80000000 |