So, if I am already using an old version before 3.11 and enable the mmap, the
data may lost after os crash. It’s that right?
原始邮件
发件人:Richard hipp...@sqlite.org
收件人:SQLite mailing listsqlite-us...@mailinglists.sqlite.org
发送时间:2016年11月3日(周四) 21:21
主题:Re: [sqlite] Is msync necessary for SQLite?
On 11/3/16, sanhua.zh sanhua...@foxmail.com 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
hipp...@sqlite.org 收件人:SQLite mailing listsqlite-us...@mailinglists.sqlite.org
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 sanhua...@foxmail.com 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
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