Really slow retrieval of manifest item by relative path with massive spines.

Question

mickael-menu-mantano opened this issue 9 years ago · comments

Mickaël Menu · Answer 1 · Wed Sep 16 2015 00:12:58 GMT+0800 (China Standard Time)

Part of this pull request is fixing this issue:
#198

Daniel Weck · Answer 2 · Wed Sep 16 2015 00:15:37 GMT+0800 (China Standard Time)

Media Overlays code reference points (copy / paste from the email discussion):

I fixed a similar performance issue a long time ago with the Media
Overlays path matcher (I resorted to a cached map).

std::map<string, std::shared_ptr<ManifestItem>> cache_smilRelativePathToManifestItem;

std::map<std::shared_ptr<ManifestItem>, string> cache_manifestItemToAbsolutePath;

So, a lot of string concatenation / manipulations occur at that point:

Also, note that when the first loop iteration fails, we have to check
for lower/upper-case percent encoding mismatches! Hopefully, your test
did not include this codepath? (otherwise it would have added a huge
processing cost)
https://github.com/readium/readium-sdk/blob/develop/ePub3/ePub/package.cpp#L173

This improved performance by an order of magnitude!

I found that this is super slow:
string::size_type i = iri.find_first_of('#');

compared to plain old:

const char * str = iri.c_str(); 
for (int j = 0; j < size; j++) 
char c = str[j]; 
if (c == '#')

See the timer I used to measure the difference:

Daniel Weck · Answer 3 · Thu Nov 19 2015 17:59:21 GMT+0800 (China Standard Time)

Closed, see PR #208