From 0b29c72bdfc1466d47567cc3191b9661f81d3d3f Mon Sep 17 00:00:00 2001 From: Julian Andres Klode Date: Sat, 26 Dec 2015 14:49:00 +0100 Subject: 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. --- apt-pkg/contrib/fileutl.cc | 6 ++---- 1 file changed, 2 insertions(+), 4 deletions(-) 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; -- cgit v1.2.3