From: Julian Andres Klode Date: Sat, 26 Dec 2015 13:49:00 +0000 (+0100) Subject: Use a hardcoded buffer size of 4096 to fix performance X-Git-Tag: 1.1.7~3 X-Git-Url: https://git.saurik.com/apt.git/commitdiff_plain/0b29c72bdfc1466d47567cc3191b9661f81d3d3f?ds=inline Use a hardcoded buffer size of 4096 to fix performance The code uses memmove() to move parts of the buffer to the front when the buffer is only partially read. By simply reading one page at a time, the maximum size of bytes that must be moved has a hard limit, and performance improves: In one test case, consisting of a 430 MB Contents file, and a 75K PDiff, applying the PDiff previously took about 48 seconds and now completes in 2 seconds. Further speed up can be achieved by buffering writes, they account for about 60% of the run-time now. --- diff --git a/apt-pkg/contrib/fileutl.cc b/apt-pkg/contrib/fileutl.cc index 928a1065a..162ad7e8d 100644 --- a/apt-pkg/contrib/fileutl.cc +++ b/apt-pkg/contrib/fileutl.cc @@ -922,7 +922,7 @@ bool ChangeOwnerAndPermissionOfFile(char const * const requester, char const * c class APT_HIDDEN FileFdPrivate { /*{{{*/ protected: FileFd * const filefd; - size_t buffersize_max = 0; + const size_t buffersize_max = 4096; std::unique_ptr buffer; unsigned long long buffersize = 0; public: @@ -984,8 +984,7 @@ public: { if (buffer.get() == nullptr) { - buffer.reset(new char[Size]); - buffersize_max = Size; + buffer.reset(new char[buffersize_max]); } unsigned long long actualread = 0; if (filefd->Read(buffer.get(), buffersize_max, &actualread) == false) @@ -994,7 +993,6 @@ public: if (buffersize == 0) { buffer.reset(nullptr); - buffersize_max = 0; if (To == InitialTo) return nullptr; break;