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NOT UPDATE FILE ON DISK Description:- When the server variable, "myisam_use_mmap" is enabled, MyISAM tables on windows are not updating the file on disk even when the server variable "flush" is set to 1. This is inturn making the table corrupted when encountering a power failure. Analysis:- When the server variable "myisam_use_mmap" is set, files of MyISAM tables will be memory mapped using the OS APIs mmap()/munmap()/msync() on Unix and CreateFileMapping() /UnmapViewOfFile()/FlushViewOfFile() on Windows. msync() and FlushViewOfFile() is responsible for flushing the changes made to the in-core copy of a file that was mapped into memory using mmap()/CreateFileMapping() back to the file system. FLUSH is determined by the OS unless explicitly called using msync()/FlushViewOfFile(). When the server variables "myisam_use_mmap" and "flush" are enabled, MyISAM is only flushing the files from file system cache to disc using "mysql_file_sync()" and not the memory mapped file from memory to FS cache using "my_msync()". ["my_msync()" inturn calls msync() on Unix and FlushViewOfFile() on Windows. Fix:- As part of the fix, if server variable "myisam_use_mmap" is enabled along with "flush", "my_msync()" is invoked to flush the data in memory to file system cache and followed by "mysql_file_sync()" which will flush the data from file system cache to disk. |
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| archive | ||
| blackhole | ||
| csv | ||
| example | ||
| federated | ||
| heap | ||
| innobase | ||
| myisam | ||
| myisammrg | ||
| ndb | ||
| perfschema | ||