save -append problem: long duration to save an existing variable in a big mat-file

Question

Emmanuel 2012-11-29

0
链接

此问题的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/55193-save-append-problem-long-duration-to-save-an-existing-variable-in-a-big-mat-file

评论： Jan 2014-5-18

Hi all,

I have a very peculiar problem with the save command. I have a lang mat-file (ca. 300 MB, compressed, created with MATLAB > 7). Now I save an additional signal in the file using

save(filename, signalname, '-append');

If the variable signalname doesn't exist in the file the copy process is very fast. But, if the file contains already a variable signalname the whole process takes too long to end (some minutes!!!). If I try to append more variables that already exist in the file, it takes evern more!! Is this a bug? Am I doing something wrong?

Thanks a lot in advance for any advice!

Emmanuel

0 个评论
显示 -2更早的评论隐藏 -2更早的评论

请先登录，再进行评论。

请先登录，再回答此问题。

Answer 1

Jan 2012-11-29

0
链接

此回答的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/55193-save-append-problem-long-duration-to-save-an-existing-variable-in-a-big-mat-file#answer_67000

This seems reasonable. Overwriting an existing variable requires to decompress the file at first to remove the old value. The larger the file, the more time is required.

You see the same problem for other compressed files also: ZIP, compressed SSDs, or a large number of books packed in a cardboard box for.

0 个评论
显示 -2更早的评论隐藏 -2更早的评论

请先登录，再进行评论。

Answer 2

Diderot 2014-5-15

0
链接

此回答的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/55193-save-append-problem-long-duration-to-save-an-existing-variable-in-a-big-mat-file#answer_136944

I got a similar problem. What's more, the new data file after several variables appended is much larger than the original, even though I only updated the previously existing variables with the same size instead of creating any new variables. This is really confusing. Would anyone share insights? Thanks!

1 个评论
显示 -1更早的评论隐藏 -1更早的评论

Jan 2014-5-18

Please do not append a new question to an existing thread. Note that you cannot accept an answer, if it is not your question and that your message is not an asnwer to the original question. Thanks.

请先登录，再进行评论。