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MDEV-22556: Incorrect result for window function when using encrypt-tmp-files=ON

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The issue here is that end_of_file for encrypted temporary IO_CACHE (used by filesort) is updated
using lseek.
Encryption adds storage overhead and hides it from the caller by recalculating offsets and lengths.
Two different IO_CACHE cannot possibly modify the same file
because the encryption key is randomly generated and stored in the IO_CACHE.
So when the tempfiles are encrypted DO NOT use lseek to change end_of_file.

Further observations about updating end_of_file using lseek
1) The end_of_file update is only used for binlog index files
2) The whole point is to update file length when the file was modified via a different file descriptor.
3) The temporary IO_CACHE files can never be modified via a different file descriptor.
4) For encrypted temporary IO_CACHE, end_of_file should not be updated with lseek
This commit is contained in:
Varun Gupta
2020-05-15 02:37:16 +05:30
parent 66f1e288a1
commit 0a5668f512
4 changed files with 47 additions and 2 deletions
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7
mysys/mf_iocache.c
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@@ -504,8 +504,11 @@ my_bool reinit_io_cache(IO_CACHE *info, enum cache_type type,
if (info->type == WRITE_CACHE)
info->end_of_file= my_b_tell(info);
else
info->end_of_file= mysql_file_seek(info->file, 0L, MY_SEEK_END,
MYF(0));
{
if (!(info->myflags & MY_ENCRYPT))
info->end_of_file= mysql_file_seek(info->file, 0L,
MY_SEEK_END, MYF(0));
}
}
/* flush cache if we want to reuse it */
if (!clear_cache && my_b_flush_io_cache(info,1))