From 4fc8d2e15b5c4915b7b8cc0f141fe227a1a5fd4c Mon Sep 17 00:00:00 2001
From: Jean-Paul Calderone <exarkun@twistedmatrix.com>
Date: Thu, 9 Dec 2021 15:39:33 -0500
Subject: [PATCH 1/2] nix-store --export/--import instead of nix-copy-closure

---
 deploy_nixos/nixos-deploy.sh | 13 ++++++++++++-
 1 file changed, 12 insertions(+), 1 deletion(-)

diff --git a/deploy_nixos/nixos-deploy.sh b/deploy_nixos/nixos-deploy.sh
index 319651b..f699610 100755
--- a/deploy_nixos/nixos-deploy.sh
+++ b/deploy_nixos/nixos-deploy.sh
@@ -62,6 +62,16 @@ copyToTarget() {
   NIX_SSHOPTS="${sshOpts[*]}" nix-copy-closure --to "$targetHost" "$@"
 }
 
+exportToTarget() {
+    nix-store --export $(nix-store --query --requisites "$1") |
+	lzma --compress |
+	pv |
+	ssh "${sshOpts[@]}" "$targetHost" '
+	    lzma --decompress |
+	    nix-store --import
+	'
+}
+
 # assumes that passwordless sudo is enabled on the server
 targetHostCmd() {
   # ${*@Q} escapes the arguments losslessly into space-separted quoted strings.
@@ -101,7 +111,8 @@ if [[ "${buildOnTarget:-false}" == true ]]; then
 
   # Upload derivation
   log "uploading derivations"
-  copyToTarget "$drvPath" --gzip --use-substitutes
+  # copyToTarget "$drvPath" --gzip --use-substitutes
+  exportToTarget "$drvPath"
 
   # Build remotely
   log "building on target"

From 992c8620b3c5d29bfa80abc769ba64405ff83012 Mon Sep 17 00:00:00 2001
From: Jean-Paul Calderone <exarkun@twistedmatrix.com>
Date: Fri, 10 Dec 2021 08:46:37 -0500
Subject: [PATCH 2/2] just use ssh compression for simplicity

also add some comments
---
 deploy_nixos/nixos-deploy.sh | 19 ++++++++++++-------
 1 file changed, 12 insertions(+), 7 deletions(-)

diff --git a/deploy_nixos/nixos-deploy.sh b/deploy_nixos/nixos-deploy.sh
index f699610..919d1f3 100755
--- a/deploy_nixos/nixos-deploy.sh
+++ b/deploy_nixos/nixos-deploy.sh
@@ -58,18 +58,19 @@ log() {
   echo "--- $*" >&2
 }
 
+# Use nix-copy-closure to copy some things to the target host.
+# nix-copy-closure avoids copying store objects that are already on the target
+# host.  It performs well when copying large objects.
 copyToTarget() {
   NIX_SSHOPTS="${sshOpts[*]}" nix-copy-closure --to "$targetHost" "$@"
 }
 
+# Use nix-store --export/--import via ssh to copy some things to the target
+# host.  This removes a lot of round-trips compared to copyToTarget which is
+# beneficial when copying many small store objects - such as .drv files.
 exportToTarget() {
     nix-store --export $(nix-store --query --requisites "$1") |
-	lzma --compress |
-	pv |
-	ssh "${sshOpts[@]}" "$targetHost" '
-	    lzma --decompress |
-	    nix-store --import
-	'
+	ssh -o Compression=yes "${sshOpts[@]}" "$targetHost" 'nix-store --import'
 }
 
 # assumes that passwordless sudo is enabled on the server
@@ -111,7 +112,8 @@ if [[ "${buildOnTarget:-false}" == true ]]; then
 
   # Upload derivation
   log "uploading derivations"
-  # copyToTarget "$drvPath" --gzip --use-substitutes
+  # Since derivations are small and there are likely many, use exportToTarget
+  # which should be faster than copyToTarget most of the time.
   exportToTarget "$drvPath"
 
   # Build remotely
@@ -127,6 +129,9 @@ else
 
   # Upload build results
   log "uploading build results"
+  # Since we are copying build outputs they are probably not all very small
+  # objects so use copyToTarget which might be able to avoid copying some of
+  # them.
   copyToTarget "$outPath" --gzip --use-substitutes
 
 fi