On 11/3/16, sanhua.zh <[email protected]> wrote:
> Here is a part of code in [unixWrite]. (os_unix.h)
> Is not it written by mmap ?
You are looking at older code that is not longer used. Look at latest
sources and you will see that the code you quote below is enclosed
within
#if defined(SQLITE_MMAP_READWRITE)
...
#endif
So writing to mmapped memory only happens if you compile with the
(undocumented, unsupported, and untested) -DSQLITE_MMAP_READWRITE
option.
>
>
> #if SQLITE_MAX_MMAP_SIZE0
> /* Deal with as much of this write request as possible by transfering
> ** data from the memory mapping using memcpy(). */
> if( offsetpFile-mmapSize ){
> if( offset+amt = pFile-mmapSize ){
> int size = -1;
> struct stat buf; /* Used to hold return values of fstat() */
> if( !osFstat(pFile-h, buf) ){
> size = (int)buf.st_size;
> }
> memcpy(((u8 *)(pFile-pMapRegion))[offset], pBuf, amt);
> return SQLITE_OK;
> }else{
> int nCopy = (int)(pFile-mmapSize - offset);
> memcpy(((u8 *)(pFile-pMapRegion))[offset], pBuf, nCopy);
> pBuf = ((u8 *)pBuf)[nCopy];
> amt -= nCopy;
> offset += nCopy;
> }
> }
> #endif
>
>
>
>
> 原始邮件
> 发件人:Richard [email protected]
> 收件人:SQLite mailing [email protected]
> 发送时间:2016年11月3日(周四) 17:49
> 主题:Re: [sqlite] Is msync necessary for SQLite?
>
>
> On 11/3/16, sanhua.zh [email protected] wrote: I run in iOS. The mmap
> is enable in recent version. So, once a mmap enable, data may lost after os
> crash unless msync. But I can’t find anywhere in the source of SQLite call
> the msync. Is it a bug? No. Mmap() is only used for reading, not writing.
> All changes are implemented by calling write() and fsync(). -- D. Richard
> Hipp [email protected] _______________________________________________
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--
D. Richard Hipp
[email protected]
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