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Commit871fe49

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Provide vectored variants of FileRead() and FileWrite().
FileReadV() and FileWriteV() adapt pg_preadv() and pg_pwritev() forfd.c's virtual file descriptors. The simple FileRead() and FileWrite()functions are now implemented in terms of the vectored functions, toavoid code duplication, and they are converted back to the correspondingsimple system calls further down (commit15c9ac3). Later work willmake more interesting multi-iovec calls.The traditional behavior of reporting a "fake" ENOSPC error issimplified. It's now always set for non-failing writes, for the benefitof callers that expect to log a meaningful "%m" if they determine thatthe write was short. (Perhaps we should consider getting rid of thatexpectation one day.)Reviewed-by: Heikki Linnakangas <hlinnaka@iki.fi>Discussion:https://postgr.es/m/CA+hUKGJkOiOCa+mag4BF+zHo7qo=o9CFheB8=g6uT5TUm2gkvA@mail.gmail.com
1 parent0c6be59 commit871fe49

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2 files changed

+54
-21
lines changed
  • src
    • backend/storage/file
    • include/storage

2 files changed

+54
-21
lines changed

‎src/backend/storage/file/fd.c

Lines changed: 25 additions & 18 deletions
Original file line numberDiff line numberDiff line change
@@ -2110,18 +2110,18 @@ FileWriteback(File file, off_t offset, off_t nbytes, uint32 wait_event_info)
21102110
}
21112111

21122112
int
2113-
FileRead(Filefile,void*buffer,size_tamount,off_toffset,
2114-
uint32wait_event_info)
2113+
FileReadV(Filefile,conststructiovec*iov,intiovcnt,off_toffset,
2114+
uint32wait_event_info)
21152115
{
21162116
intreturnCode;
21172117
Vfd*vfdP;
21182118

21192119
Assert(FileIsValid(file));
21202120

2121-
DO_DB(elog(LOG,"FileRead: %d (%s) "INT64_FORMAT" %zu %p",
2121+
DO_DB(elog(LOG,"FileReadV: %d (%s) "INT64_FORMAT" %d",
21222122
file,VfdCache[file].fileName,
21232123
(int64)offset,
2124-
amount,buffer));
2124+
iovcnt));
21252125

21262126
returnCode=FileAccess(file);
21272127
if (returnCode<0)
@@ -2131,7 +2131,7 @@ FileRead(File file, void *buffer, size_t amount, off_t offset,
21312131

21322132
retry:
21332133
pgstat_report_wait_start(wait_event_info);
2134-
returnCode=pg_pread(vfdP->fd,buffer,amount,offset);
2134+
returnCode=pg_preadv(vfdP->fd,iov,iovcnt,offset);
21352135
pgstat_report_wait_end();
21362136

21372137
if (returnCode<0)
@@ -2166,18 +2166,18 @@ FileRead(File file, void *buffer, size_t amount, off_t offset,
21662166
}
21672167

21682168
int
2169-
FileWrite(Filefile,constvoid*buffer,size_tamount,off_toffset,
2170-
uint32wait_event_info)
2169+
FileWriteV(Filefile,conststructiovec*iov,intiovcnt,off_toffset,
2170+
uint32wait_event_info)
21712171
{
21722172
intreturnCode;
21732173
Vfd*vfdP;
21742174

21752175
Assert(FileIsValid(file));
21762176

2177-
DO_DB(elog(LOG,"FileWrite: %d (%s) "INT64_FORMAT" %zu %p",
2177+
DO_DB(elog(LOG,"FileWriteV: %d (%s) "INT64_FORMAT" %d",
21782178
file,VfdCache[file].fileName,
21792179
(int64)offset,
2180-
amount,buffer));
2180+
iovcnt));
21812181

21822182
returnCode=FileAccess(file);
21832183
if (returnCode<0)
@@ -2195,7 +2195,10 @@ FileWrite(File file, const void *buffer, size_t amount, off_t offset,
21952195
*/
21962196
if (temp_file_limit >=0&& (vfdP->fdstate&FD_TEMP_FILE_LIMIT))
21972197
{
2198-
off_tpast_write=offset+amount;
2198+
off_tpast_write=offset;
2199+
2200+
for (inti=0;i<iovcnt;++i)
2201+
past_write+=iov[i].iov_len;
21992202

22002203
if (past_write>vfdP->fileSize)
22012204
{
@@ -2211,23 +2214,27 @@ FileWrite(File file, const void *buffer, size_t amount, off_t offset,
22112214
}
22122215

22132216
retry:
2214-
errno=0;
22152217
pgstat_report_wait_start(wait_event_info);
2216-
returnCode=pg_pwrite(VfdCache[file].fd,buffer,amount,offset);
2218+
returnCode=pg_pwritev(vfdP->fd,iov,iovcnt,offset);
22172219
pgstat_report_wait_end();
22182220

2219-
/* if write didn't set errno, assume problem is no disk space */
2220-
if (returnCode!=amount&&errno==0)
2221-
errno=ENOSPC;
2222-
22232221
if (returnCode >=0)
22242222
{
2223+
/*
2224+
* Some callers expect short writes to set errno, and traditionally we
2225+
* have assumed that they imply disk space shortage. We don't want to
2226+
* waste CPU cycles adding up the total size here, so we'll just set
2227+
* it for all successful writes in case such a caller determines that
2228+
* the write was short and ereports "%m".
2229+
*/
2230+
errno=ENOSPC;
2231+
22252232
/*
22262233
* Maintain fileSize and temporary_files_size if it's a temp file.
22272234
*/
22282235
if (vfdP->fdstate&FD_TEMP_FILE_LIMIT)
22292236
{
2230-
off_tpast_write=offset+amount;
2237+
off_tpast_write=offset+returnCode;
22312238

22322239
if (past_write>vfdP->fileSize)
22332240
{
@@ -2239,7 +2246,7 @@ FileWrite(File file, const void *buffer, size_t amount, off_t offset,
22392246
else
22402247
{
22412248
/*
2242-
* See comments inFileRead()
2249+
* See comments inFileReadV()
22432250
*/
22442251
#ifdefWIN32
22452252
DWORDerror=GetLastError();

‎src/include/storage/fd.h

Lines changed: 29 additions & 3 deletions
Original file line numberDiff line numberDiff line change
@@ -15,7 +15,7 @@
1515
/*
1616
* calls:
1717
*
18-
*File {Close, Read, Write, Size, Sync}
18+
*File {Close, Read,ReadV,Write, WriteV, Size, Sync}
1919
*{Path Name Open, Allocate, Free} File
2020
*
2121
* These are NOT JUST RENAMINGS OF THE UNIX ROUTINES.
@@ -43,6 +43,8 @@
4343
#ifndefFD_H
4444
#defineFD_H
4545

46+
#include"port/pg_iovec.h"
47+
4648
#include<dirent.h>
4749
#include<fcntl.h>
4850

@@ -105,8 +107,8 @@ extern File PathNameOpenFilePerm(const char *fileName, int fileFlags, mode_t fil
105107
externFileOpenTemporaryFile(boolinterXact);
106108
externvoidFileClose(Filefile);
107109
externintFilePrefetch(Filefile,off_toffset,off_tamount,uint32wait_event_info);
108-
externintFileRead(Filefile,void*buffer,size_tamount,off_toffset,uint32wait_event_info);
109-
externintFileWrite(Filefile,constvoid*buffer,size_tamount,off_toffset,uint32wait_event_info);
110+
externintFileReadV(Filefile,conststructiovec*ioc,intiovcnt,off_toffset,uint32wait_event_info);
111+
externintFileWriteV(Filefile,conststructiovec*ioc,intiovcnt,off_toffset,uint32wait_event_info);
110112
externintFileSync(Filefile,uint32wait_event_info);
111113
externintFileZero(Filefile,off_toffset,off_tamount,uint32wait_event_info);
112114
externintFileFallocate(Filefile,off_toffset,off_tamount,uint32wait_event_info);
@@ -189,4 +191,28 @@ extern intdurable_unlink(const char *fname, int elevel);
189191
externvoidSyncDataDirectory(void);
190192
externintdata_sync_elevel(intelevel);
191193

194+
staticinlineint
195+
FileRead(Filefile,void*buffer,size_tamount,off_toffset,
196+
uint32wait_event_info)
197+
{
198+
structioveciov= {
199+
.iov_base=buffer,
200+
.iov_len=amount
201+
};
202+
203+
returnFileReadV(file,&iov,1,offset,wait_event_info);
204+
}
205+
206+
staticinlineint
207+
FileWrite(Filefile,constvoid*buffer,size_tamount,off_toffset,
208+
uint32wait_event_info)
209+
{
210+
structioveciov= {
211+
.iov_base=unconstify(void*,buffer),
212+
.iov_len=amount
213+
};
214+
215+
returnFileWriteV(file,&iov,1,offset,wait_event_info);
216+
}
217+
192218
#endif/* FD_H */

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