Much more cmake processes when sccache is enabled (because build becomes IO bound task)

Author: mariadb-AlexanderPresniakov

.drone.jsonnet

@@ -718,6 +718,7 @@ local Pipeline(branch, platform, event, arch='amd64', server='10.6-enterprise')
              ],
            },
            {
+            // Get the copy of compile cache from the nightly build from S3
              name: 'get-local-sccache',
              depends_on: ['submodules'],
              image: 'amazon/aws-cli',
@@ -737,7 +738,10 @@ local Pipeline(branch, platform, event, arch='amd64', server='10.6-enterprise')
                'if aws s3 cp s3://cspkg/nightly-sccache/stable-23.10-' + server + '-' + arch + '-' + std.strReplace(platform, ":", "-") + '/sccache.tar.zst /tmp/sccache.tar.zst; then',
                '  echo "SCCache archive found. Extracting..."',
                '  tar -I zstd -xf /tmp/sccache.tar.zst -C /mdb/sccache',
-               '  ls /mdb/sccache/ && mv /mdb/sccache/mdb/sccache /mdb/sccache_inner && rm -rf /mdb/sccache/ && mv /mdb/sccache_inner /mdb/sccache',  # TODO remove
+
+                // TODO remove when all correct caches are uploaded
+               '  ls /mdb/sccache/; if [ -f /mdb/sccache/mdb ]; then mv /mdb/sccache/mdb/sccache /mdb/sccache_inner && rm -rf /mdb/sccache/ && mv /mdb/sccache_inner /mdb/sccache; fi',
+
                '  echo "SCCache successfully downloaded and extracted."',
                '  ls /mdb/sccache',
                'else',

build/bootstrap_mcs.sh

@@ -317,6 +317,11 @@ construct_cmake_flags() {
 
     if [[ $SCCACHE = true ]]; then
         warn "Use sccache"
+        # If sccache works well, the build becomes an IO bound task instead of CPU bound
+        # It happens because most of the time is spent is hashing the input files
+        # So we can run more jobs in parallel
+        CPUS=$((CPUS * 3))
+        message "Adjusted the number of CPUs for parallel build to $CPUS (multiplied by 3 to reduce IO wait)"
         MDB_CMAKE_FLAGS="${MDB_CMAKE_FLAGS} -DCMAKE_C_COMPILER_LAUNCHER=sccache -DCMAKE_CXX_COMPILER_LAUNCHER=sccache"
     fi