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Provide pg_preadv() and pg_pwritev().

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Provide synchronous vectored file I/O routines.  These map to preadv()
and pwritev(), with fallback implementations for systems that don't have
them.  Also provide a wrapper pg_pwritev_with_retry() that automatically
retries on short writes.

Reviewed-by: Tom Lane <tgl@sss.pgh.pa.us>
Reviewed-by: Andres Freund <andres@anarazel.de>
Discussion: https://postgr.es/m/CA%2BhUKGJA%2Bu-220VONeoREBXJ9P3S94Y7J%2BkqCnTYmahvZJwM%3Dg%40mail.gmail.com
This commit is contained in:
Thomas Munro
2021-01-11 14:37:13 +13:00
parent 01334c92fa
commit 13a021f3e8
9 changed files with 238 additions and 34 deletions
Download Patch File Download Diff File Expand all files Collapse all files

15
src/include/pg_config.h.in
View File

@ -412,6 +412,9 @@
/* Define to 1 if you have the `pread' function. */
#undef HAVE_PREAD
/* Define to 1 if you have the `preadv' function. */
#undef HAVE_PREADV
/* Define to 1 if you have the `pstat' function. */
#undef HAVE_PSTAT
@ -430,6 +433,9 @@
/* Define to 1 if you have the `pwrite' function. */
#undef HAVE_PWRITE
/* Define to 1 if you have the `pwritev' function. */
#undef HAVE_PWRITEV
/* Define to 1 if you have the `random' function. */
#undef HAVE_RANDOM
@ -445,6 +451,9 @@
/* Define to 1 if you have the `readlink' function. */
#undef HAVE_READLINK
/* Define to 1 if you have the `readv' function. */
#undef HAVE_READV
/* Define to 1 if you have the global variable
'rl_completion_append_character'. */
#undef HAVE_RL_COMPLETION_APPEND_CHARACTER
@ -629,6 +638,9 @@
/* Define to 1 if you have the <sys/ucred.h> header file. */
#undef HAVE_SYS_UCRED_H
/* Define to 1 if you have the <sys/uio.h> header file. */
#undef HAVE_SYS_UIO_H
/* Define to 1 if you have the <sys/un.h> header file. */
#undef HAVE_SYS_UN_H
@ -683,6 +695,9 @@
/* Define to 1 if you have the <winldap.h> header file. */
#undef HAVE_WINLDAP_H
/* Define to 1 if you have the `writev' function. */
#undef HAVE_WRITEV
/* Define to 1 if you have the `X509_get_signature_nid' function. */
#undef HAVE_X509_GET_SIGNATURE_NID

2
src/include/port.h
View File

@ -431,6 +431,8 @@ extern ssize_t pg_pread(int fd, void *buf, size_t nbyte, off_t offset);
extern ssize_t pg_pwrite(int fd, const void *buf, size_t nbyte, off_t offset);
#endif
/* For pg_pwritev() and pg_preadv(), see port/pg_iovec.h. */
#if !HAVE_DECL_STRLCAT
extern size_t strlcat(char *dst, const char *src, size_t siz);
#endif

59
src/include/port/pg_iovec.h Normal file
View File

@ -0,0 +1,59 @@
/*-------------------------------------------------------------------------
*
* pg_iovec.h
* Header for the vectored I/O functions in src/port/p{read,write}.c.
*
* Portions Copyright (c) 1996-2020, PostgreSQL Global Development Group
* Portions Copyright (c) 1994, Regents of the University of California
*
* src/include/port/pg_iovec.h
*
*-------------------------------------------------------------------------
*/
#ifndef PG_IOVEC_H
#define PG_IOVEC_H
#include <limits.h>
#ifdef HAVE_SYS_UIO_H
#include <sys/uio.h>
#endif
/* If <sys/uio.h> is missing, define our own POSIX-compatible iovec struct. */
#ifndef HAVE_SYS_UIO_H
struct iovec
{
void *iov_base;
size_t iov_len;
};
#endif
/*
* If <limits.h> didn't define IOV_MAX, define our own. POSIX requires at
* least 16.
*/
#ifndef IOV_MAX
#define IOV_MAX 16
#endif
/* Define a reasonable maximum that is safe to use on the stack. */
#define PG_IOV_MAX Min(IOV_MAX, 32)
#ifdef HAVE_PREADV
#define pg_preadv preadv
#else
extern ssize_t pg_preadv(int fd, const struct iovec *iov, int iovcnt, off_t offset);
#endif
#ifdef HAVE_PWRITEV
#define pg_pwritev pwritev
#else
extern ssize_t pg_pwritev(int fd, const struct iovec *iov, int iovcnt, off_t offset);
#endif
extern ssize_t pg_pwritev_with_retry(int fd,
const struct iovec *iov,
int iovcnt,
off_t offset);
#endif /* PG_IOVEC_H */

2
src/port/Makefile
View File

@ -53,6 +53,8 @@ OBJS = \
pgstrcasecmp.o \
pgstrsignal.o \
pqsignal.o \
pread.o \
pwrite.o \
qsort.o \
qsort_arg.o \
quotes.o \

43
src/port/pread.c
View File

@ -1,7 +1,7 @@
/*-------------------------------------------------------------------------
*
* pread.c
* Implementation of pread(2) for platforms that lack one.
* Implementation of pread[v](2) for platforms that lack one.
*
* Portions Copyright (c) 1996-2021, PostgreSQL Global Development Group
*
@ -9,7 +9,8 @@
* src/port/pread.c
*
* Note that this implementation changes the current file position, unlike
* the POSIX function, so we use the name pg_pread().
* the POSIX function, so we use the name pg_pread(). Likewise for the
* iovec version.
*
*-------------------------------------------------------------------------
*/
@ -23,6 +24,9 @@
#include <unistd.h>
#endif
#include "port/pg_iovec.h"
#ifndef HAVE_PREAD
ssize_t
pg_pread(int fd, void *buf, size_t size, off_t offset)
{
@ -56,3 +60,38 @@ pg_pread(int fd, void *buf, size_t size, off_t offset)
return read(fd, buf, size);
#endif
}
#endif
#ifndef HAVE_PREADV
ssize_t
pg_preadv(int fd, const struct iovec *iov, int iovcnt, off_t offset)
{
#ifdef HAVE_READV
if (iovcnt == 1)
return pg_pread(fd, iov[0].iov_base, iov[0].iov_len, offset);
if (lseek(fd, offset, SEEK_SET) < 0)
return -1;
return readv(fd, iov, iovcnt);
#else
ssize_t sum = 0;
ssize_t part;
for (int i = 0; i < iovcnt; ++i)
{
part = pg_pread(fd, iov[i].iov_base, iov[i].iov_len, offset);
if (part < 0)
{
if (i == 0)
return -1;
else
return sum;
}
sum += part;
offset += part;
if (part < iov[i].iov_len)
return sum;
}
return sum;
#endif
}
#endif

107
src/port/pwrite.c
View File

@ -1,7 +1,7 @@
/*-------------------------------------------------------------------------
*
* pwrite.c
* Implementation of pwrite(2) for platforms that lack one.
* Implementation of pwrite[v](2) for platforms that lack one.
*
* Portions Copyright (c) 1996-2021, PostgreSQL Global Development Group
*
@ -9,7 +9,8 @@
* src/port/pwrite.c
*
* Note that this implementation changes the current file position, unlike
* the POSIX function, so we use the name pg_pwrite().
* the POSIX function, so we use the name pg_pwrite(). Likewise for the
* iovec version.
*
*-------------------------------------------------------------------------
*/
@ -23,6 +24,9 @@
#include <unistd.h>
#endif
#include "port/pg_iovec.h"
#ifndef HAVE_PWRITE
ssize_t
pg_pwrite(int fd, const void *buf, size_t size, off_t offset)
{
@ -53,3 +57,102 @@ pg_pwrite(int fd, const void *buf, size_t size, off_t offset)
return write(fd, buf, size);
#endif
}
#endif
#ifndef HAVE_PWRITEV
ssize_t
pg_pwritev(int fd, const struct iovec *iov, int iovcnt, off_t offset)
{
#ifdef HAVE_WRITEV
if (iovcnt == 1)
return pg_pwrite(fd, iov[0].iov_base, iov[0].iov_len, offset);
if (lseek(fd, offset, SEEK_SET) < 0)
return -1;
return writev(fd, iov, iovcnt);
#else
ssize_t sum = 0;
ssize_t part;
for (int i = 0; i < iovcnt; ++i)
{
part = pg_pwrite(fd, iov[i].iov_base, iov[i].iov_len, offset);
if (part < 0)
{
if (i == 0)
return -1;
else
return sum;
}
sum += part;
offset += part;
if (part < iov[i].iov_len)
return sum;
}
return sum;
#endif
}
#endif
/*
* A convenience wrapper for pg_pwritev() that retries on partial write. If an
* error is returned, it is unspecified how much has been written.
*/
ssize_t
pg_pwritev_with_retry(int fd, const struct iovec *iov, int iovcnt, off_t offset)
{
struct iovec iov_copy[PG_IOV_MAX];
ssize_t sum = 0;
ssize_t part;
/* We'd better have space to make a copy, in case we need to retry. */
if (iovcnt > PG_IOV_MAX)
{
errno = EINVAL;
return -1;
}
for (;;)
{
/* Write as much as we can. */
part = pg_pwritev(fd, iov, iovcnt, offset);
if (part < 0)
return -1;
#ifdef SIMULATE_SHORT_WRITE
part = Min(part, 4096);
#endif
/* Count our progress. */
sum += part;
offset += part;
/* Step over iovecs that are done. */
while (iovcnt > 0 && iov->iov_len <= part)
{
part -= iov->iov_len;
++iov;
--iovcnt;
}
/* Are they all done? */
if (iovcnt == 0)
{
if (part > 0)
elog(ERROR, "unexpectedly wrote more than requested");
break;
}
/*
* Move whatever's left to the front of our mutable copy and adjust the
* leading iovec.
*/
Assert(iovcnt > 0);
memmove(iov_copy, iov, sizeof(*iov) * iovcnt);
Assert(iov->iov_len > part);
iov_copy[0].iov_base = (char *) iov_copy[0].iov_base + part;
iov_copy[0].iov_len -= part;
iov = iov_copy;
}
return sum;
}

5
src/tools/msvc/Solution.pm
View File

@ -329,17 +329,20 @@ sub GenerateFiles
HAVE_PPC_LWARX_MUTEX_HINT => undef,
HAVE_PPOLL => undef,
HAVE_PREAD => undef,
HAVE_PREADV => undef,
HAVE_PSTAT => undef,
HAVE_PS_STRINGS => undef,
HAVE_PTHREAD => undef,
HAVE_PTHREAD_IS_THREADED_NP => undef,
HAVE_PTHREAD_PRIO_INHERIT => undef,
HAVE_PWRITE => undef,
HAVE_PWRITEV => undef,
HAVE_RANDOM => undef,
HAVE_READLINE_H => undef,
HAVE_READLINE_HISTORY_H => undef,
HAVE_READLINE_READLINE_H => undef,
HAVE_READLINK => undef,
HAVE_READV => undef,
HAVE_RL_COMPLETION_APPEND_CHARACTER => undef,
HAVE_RL_COMPLETION_MATCHES => undef,
HAVE_RL_COMPLETION_SUPPRESS_QUOTE => undef,
@ -400,6 +403,7 @@ sub GenerateFiles
HAVE_SYS_TAS_H => undef,
HAVE_SYS_TYPES_H => 1,
HAVE_SYS_UCRED_H => undef,
HAVE_SYS_UIO_H => undef,
HAVE_SYS_UN_H => undef,
HAVE_TERMIOS_H => undef,
HAVE_TYPEOF => undef,
@ -418,6 +422,7 @@ sub GenerateFiles
HAVE_WINLDAP_H => undef,
HAVE_WCSTOMBS_L => 1,
HAVE_WCTYPE_H => 1,
HAVE_WRITEV => undef,
HAVE_X509_GET_SIGNATURE_NID => 1,
HAVE_X86_64_POPCNTQ => undef,
HAVE__BOOL => undef,