The conflict handling in current Pacman implementation is not very good performance-wise.

Here's another patch that speeds things up a bit. :) Patches are for 2.9 but I had no trouble applying them to 2.9.2.

'pacman' is 2.9.2, the other one is this + list handling performance patches.

Try to add an already installed package:
========================================

# pwd
/var/cache/pacman/pkg

# time pacman -A xorg*

loading package data... done.
checking for file conflicts... done.
error: xorg is already installed. (try --upgrade)

real 0m6.317s
user 0m5.703s
sys 0m0.236s


# time /var/abs/base/pacman/src/pacman-2.9/pacman -A xorg*

loading package data... done.
checking for file conflicts... done.
error: xorg is already installed. (try --upgrade)

real 0m0.352s
user 0m0.153s
sys 0m0.181s


Try to add several already installed packages:
==============================================

# time pacman -A w* kde*

loading package data... done.
checking for file conflicts... done.
error: wget is already installed. (try --upgrade)
error: windowmaker is already installed. (try --upgrade)
error: wine is already installed. (try --upgrade)
error: wireless_tools is already installed. (try --upgrade)
error: wxgtk is already installed. (try --upgrade)
error: wxpython is already installed. (try --upgrade)
error: kdelibs is already installed. (try --upgrade)
error: kdemultimedia is already installed. (try --upgrade)
error: kdebase is already installed. (try --upgrade)
error: kdeaddons is already installed. (try --upgrade)
error: kdeartwork is already installed. (try --upgrade)
error: kdegames is already installed. (try --upgrade)
error: kdegraphics is already installed. (try --upgrade)
error: kdenetwork is already installed. (try --upgrade)
error: kdesdk is already installed. (try --upgrade)
error: kdeutils is already installed. (try --upgrade)

real 1m40.585s
user 1m36.179s
sys 0m1.825s


# time /var/abs/base/pacman/src/pacman-2.9/pacman -A w* kde*

loading package data... done.
checking for file conflicts... done.
error: wget is already installed. (try --upgrade)
error: windowmaker is already installed. (try --upgrade)
error: wine is already installed. (try --upgrade)
error: wireless_tools is already installed. (try --upgrade)
error: wxgtk is already installed. (try --upgrade)
error: wxpython is already installed. (try --upgrade)
error: kdelibs is already installed. (try --upgrade)
error: kdemultimedia is already installed. (try --upgrade)
error: kdebase is already installed. (try --upgrade)
error: kdeaddons is already installed. (try --upgrade)
error: kdeartwork is already installed. (try --upgrade)
error: kdegames is already installed. (try --upgrade)
error: kdegraphics is already installed. (try --upgrade)
error: kdenetwork is already installed. (try --upgrade)
error: kdesdk is already installed. (try --upgrade)
error: kdeutils is already installed. (try --upgrade)

real 0m2.034s
user 0m1.144s
sys 0m0.774s



Enable extra checking, commented out in the code:
=================================================

# time /var/abs/base/pacman/src/pacman-2.9/pacman -A libsoup22-2.1.13-1.pkg.tar.gz

loading package data... done.
checking for file conflicts...
error: the following file conflicts were found:
opt/gnome/include/libsoup-2.2/libsoup/soup-address.h: exists in "libsoup22" (target) and "libsoup" (installed)
opt/gnome/include/libsoup-2.2/libsoup/soup-connection.h: exists in "libsoup22" (target) and "libsoup" (installed)
opt/gnome/include/libsoup-2.2/libsoup/soup-headers.h: exists in "libsoup22" (target) and "libsoup" (installed)
opt/gnome/include/libsoup-2.2/libsoup/soup-message-filter.h: exists in "libsoup22" (target) and "libsoup" (installed)
opt/gnome/include/libsoup-2.2/libsoup/soup-message-queue.h: exists in "libsoup22" (target) and "libsoup" (installed)
opt/gnome/include/libsoup-2.2/libsoup/soup-message.h: exists in "libsoup22" (target) and "libsoup" (installed)
opt/gnome/include/libsoup-2.2/libsoup/soup-method.h: exists in "libsoup22" (target) and "libsoup" (installed)
opt/gnome/include/libsoup-2.2/libsoup/soup-misc.h: exists in "libsoup22" (target) and "libsoup" (installed)
opt/gnome/include/libsoup-2.2/libsoup/soup-server-auth.h: exists in "libsoup22" (target) and "libsoup" (installed)
opt/gnome/include/libsoup-2.2/libsoup/soup-server-message.h: exists in "libsoup22" (target) and "libsoup" (installed)

[...]

errors occurred, no packages were upgraded.

real 0m0.399s
user 0m0.266s
sys 0m0.117s


# time pacman -A libsoup22-2.1.13-1.pkg.tar.gz

loading package data... done.
checking for file conflicts...
error: the following file conflicts were found:
libsoup22: /opt/gnome/include/libsoup-2.2/libsoup/soup-address.h: exists in filesystem
libsoup22: /opt/gnome/include/libsoup-2.2/libsoup/soup-connection.h: exists in filesystem
libsoup22: /opt/gnome/include/libsoup-2.2/libsoup/soup-headers.h: exists in filesystem
libsoup22: /opt/gnome/include/libsoup-2.2/libsoup/soup-message-filter.h: exists in filesystem
libsoup22: /opt/gnome/include/libsoup-2.2/libsoup/soup-message-queue.h: exists in filesystem
libsoup22: /opt/gnome/include/libsoup-2.2/libsoup/soup-message.h: exists in filesystem
libsoup22: /opt/gnome/include/libsoup-2.2/libsoup/soup-method.h: exists in filesystem
libsoup22: /opt/gnome/include/libsoup-2.2/libsoup/soup-misc.h: exists in filesystem
libsoup22: /opt/gnome/include/libsoup-2.2/libsoup/soup-server-auth.h: exists in filesystem

[...]

errors occurred, no packages were upgraded.

real 0m0.185s
user 0m0.048s
sys 0m0.132s