diff --git a/azure-pipelines.yml b/azure-pipelines.yml
index a0cdd50d6fa36..66703c3596b95 100644
--- a/azure-pipelines.yml
+++ b/azure-pipelines.yml
@@ -40,8 +40,9 @@ resources:
   # see https://github.com/apache/flink-connector-shared-utils/tree/ci_utils
   - container: flink-build-container
     image: apache/flink-ci-docker:java_8_11_17_21_25_maven_386_jammy
-    # On AZP provided machines, set this flag to allow writing coredumps in docker
-    options: --privileged
+    # On AZP provided machines, set this flag to allow writing coredumps in docker.
+    # --tmpfs provides RAM-backed scratch; the Machine info step reports whether the agent honours it.
+    options: --privileged --tmpfs /mnt/ram:size=24g,exec,mode=1777
 
 # Define variables:
 # - See tools/azure-pipelines/jobs-template.yml for a short summary of the caching
@@ -84,6 +85,8 @@ stages:
         pool:
           vmImage: 'ubuntu-24.04'
         steps:
+          - script: ./tools/ci/print_machine_info.sh
+            displayName: Machine info
           - task: GoTool@0
             inputs:
               version: '1.18.1'
diff --git a/flink-filesystems/flink-azure-fs-hadoop/pom.xml b/flink-filesystems/flink-azure-fs-hadoop/pom.xml
index 9794679b181b6..21436521ab027 100644
--- a/flink-filesystems/flink-azure-fs-hadoop/pom.xml
+++ b/flink-filesystems/flink-azure-fs-hadoop/pom.xml
@@ -134,6 +134,8 @@ under the License.
 							<goal>shade</goal>
 						</goals>
 						<configuration>
+							<!-- Skippable so the fast CI compile can drop this FS-plugin shade off the critical path -->
+							<skip>${flink.fsShade.skip}</skip>
 							<artifactSet>
 								<includes>
 									<include>*:*</include>
diff --git a/flink-filesystems/flink-gs-fs-hadoop/pom.xml b/flink-filesystems/flink-gs-fs-hadoop/pom.xml
index ec92c44dfae04..0b80e2aa1c01f 100644
--- a/flink-filesystems/flink-gs-fs-hadoop/pom.xml
+++ b/flink-filesystems/flink-gs-fs-hadoop/pom.xml
@@ -222,6 +222,8 @@ under the License.
 							<goal>shade</goal>
 						</goals>
 						<configuration>
+							<!-- Skippable so the fast CI compile can drop this FS-plugin shade off the critical path -->
+							<skip>${flink.fsShade.skip}</skip>
 							<artifactSet>
 								<includes>
 									<include>*:*</include>
diff --git a/flink-filesystems/flink-oss-fs-hadoop/pom.xml b/flink-filesystems/flink-oss-fs-hadoop/pom.xml
index d6bb8c51a3ca3..f202f061d3db2 100644
--- a/flink-filesystems/flink-oss-fs-hadoop/pom.xml
+++ b/flink-filesystems/flink-oss-fs-hadoop/pom.xml
@@ -151,6 +151,8 @@ under the License.
 							<goal>shade</goal>
 						</goals>
 						<configuration>
+							<!-- Skippable so the fast CI compile can drop this FS-plugin shade off the critical path -->
+							<skip>${flink.fsShade.skip}</skip>
 							<artifactSet>
 								<includes>
 									<include>*:*</include>
diff --git a/flink-filesystems/flink-s3-fs-hadoop/pom.xml b/flink-filesystems/flink-s3-fs-hadoop/pom.xml
index 098296e49561a..0220b54f23978 100644
--- a/flink-filesystems/flink-s3-fs-hadoop/pom.xml
+++ b/flink-filesystems/flink-s3-fs-hadoop/pom.xml
@@ -246,6 +246,8 @@ under the License.
 							<goal>shade</goal>
 						</goals>
 						<configuration>
+							<!-- Skippable so the fast CI compile can drop this FS-plugin shade off the critical path -->
+							<skip>${flink.fsShade.skip}</skip>
 							<artifactSet>
 								<includes>
 									<include>*:*</include>
diff --git a/flink-filesystems/flink-s3-fs-native/pom.xml b/flink-filesystems/flink-s3-fs-native/pom.xml
index b0403112df036..12ad537f649dc 100644
--- a/flink-filesystems/flink-s3-fs-native/pom.xml
+++ b/flink-filesystems/flink-s3-fs-native/pom.xml
@@ -179,6 +179,8 @@ under the License.
 							<goal>shade</goal>
 						</goals>
 						<configuration>
+							<!-- Skippable so the fast CI compile can drop this FS-plugin shade off the critical path -->
+							<skip>${flink.fsShade.skip}</skip>
 							<artifactSet>
 								<includes>
 									<include>software.amazon.awssdk:*</include>
diff --git a/flink-filesystems/flink-s3-fs-presto/pom.xml b/flink-filesystems/flink-s3-fs-presto/pom.xml
index cb3236ce1a67c..a6c6fdbe7b15c 100644
--- a/flink-filesystems/flink-s3-fs-presto/pom.xml
+++ b/flink-filesystems/flink-s3-fs-presto/pom.xml
@@ -641,6 +641,8 @@ under the License.
 							<goal>shade</goal>
 						</goals>
 						<configuration>
+							<!-- Skippable so the fast CI compile can drop this FS-plugin shade off the critical path -->
+							<skip>${flink.fsShade.skip}</skip>
 							<artifactSet>
 								<includes>
 									<include>*:*</include>
diff --git a/pom.xml b/pom.xml
index b67166326c562..cd6c14f0c9c81 100644
--- a/pom.xml
+++ b/pom.xml
@@ -131,6 +131,8 @@ under the License.
 		<flink.shaded.jackson.version>2.20.1</flink.shaded.jackson.version>
 		<flink.shaded.jsonpath.version>2.10.0</flink.shaded.jsonpath.version>
 		<flink.markBundledAsOptional>true</flink.markBundledAsOptional>
+		<!-- Default false = normal shade; the fast CI compile sets it true to skip the FS-plugin shade off the critical path (see tools/ci/compile.sh) -->
+		<flink.fsShade.skip>false</flink.fsShade.skip>
 		<source.java.version>11</source.java.version>
 		<target.java.version>17</target.java.version>
 		<slf4j.version>1.7.36</slf4j.version>
diff --git a/tools/azure-pipelines/build-apache-repo.yml b/tools/azure-pipelines/build-apache-repo.yml
index 5befcf292c69f..07e5d03fec448 100644
--- a/tools/azure-pipelines/build-apache-repo.yml
+++ b/tools/azure-pipelines/build-apache-repo.yml
@@ -40,6 +40,8 @@ resources:
   # see https://github.com/apache/flink-connector-shared-utils/tree/ci_utils
   - container: flink-build-container
     image: apache/flink-ci-docker:java_8_11_17_21_25_maven_386_jammy
+    # RAM-backed scratch for the build; the Machine info step reports whether the agent honours it.
+    options: --tmpfs /mnt/ram:size=24g,exec,mode=1777
 
 variables:
   MAVEN_CACHE_FOLDER: $(Pipeline.Workspace)/.m2/repository
@@ -77,6 +79,8 @@ stages:
         pool:
           vmImage: 'ubuntu-24.04'
         steps:
+          - script: ./tools/ci/print_machine_info.sh
+            displayName: Machine info
           # Skip docs check if this is a pull request that doesn't contain a documentation change
           - task: GoTool@0
             inputs:
@@ -167,6 +171,8 @@ stages:
         pool:
           vmImage: 'ubuntu-24.04'
         steps:
+          - script: ./tools/ci/print_machine_info.sh
+            displayName: Machine info
           - task: GoTool@0
             inputs:
               version: '1.18.1'
diff --git a/tools/azure-pipelines/build-nightly-dist.yml b/tools/azure-pipelines/build-nightly-dist.yml
index c3c7849a70ac2..775cc84b17bde 100644
--- a/tools/azure-pipelines/build-nightly-dist.yml
+++ b/tools/azure-pipelines/build-nightly-dist.yml
@@ -24,6 +24,8 @@ jobs:
     workspace:
       clean: all
     steps:
+      - script: ./tools/ci/print_machine_info.sh
+        displayName: Machine info
       # free up disk space on the hosted agent; the full dist build plus the
       # Maven cache does not fit in the ~16 GB the image leaves free
       - script: ./tools/azure-pipelines/free_disk_space.sh
@@ -82,6 +84,8 @@ jobs:
     workspace:
       clean: all
     steps:
+      - script: ./tools/ci/print_machine_info.sh
+        displayName: Machine info
       # free up disk space on the hosted agent; the snapshot deploy build plus
       # the Maven cache does not fit in the ~16 GB the image leaves free
       - script: ./tools/azure-pipelines/free_disk_space.sh
diff --git a/tools/azure-pipelines/build-python-wheels.yml b/tools/azure-pipelines/build-python-wheels.yml
index 418bdeb88c2ea..a0fdc78b961ad 100644
--- a/tools/azure-pipelines/build-python-wheels.yml
+++ b/tools/azure-pipelines/build-python-wheels.yml
@@ -18,6 +18,8 @@ jobs:
     pool:
       vmImage: 'ubuntu-24.04'
     steps:
+      - script: ./tools/ci/print_machine_info.sh
+        displayName: Machine info
       - task: UsePythonVersion@0
         inputs:
           versionSpec: '3.12'
@@ -34,6 +36,8 @@ jobs:
     pool:
       vmImage: 'macOS-latest'
     steps:
+      - script: ./tools/ci/print_machine_info.sh
+        displayName: Machine info
       - task: UsePythonVersion@0
         inputs:
           versionSpec: '3.12'
diff --git a/tools/azure-pipelines/e2e-template.yml b/tools/azure-pipelines/e2e-template.yml
index dcffa9b36a072..9898720d52215 100644
--- a/tools/azure-pipelines/e2e-template.yml
+++ b/tools/azure-pipelines/e2e-template.yml
@@ -44,6 +44,8 @@ jobs:
       .gitattributes
       .github/**
   steps:
+    - script: ./tools/ci/print_machine_info.sh
+      displayName: Machine info
     # Skip e2e test execution if this is a documentation only pull request (master / release builds will still be checked regularly)
     - bash: |
         source ./tools/azure-pipelines/build_properties.sh
@@ -140,7 +142,8 @@ jobs:
         sudo apt install ./libssl1.0.0_*.deb
       displayName: Prepare E2E run
       condition: not(eq(variables['SKIP'], '1'))
-    - script: ${{parameters.environment}} PROFILE="$PROFILE -Dfast -Pskip-webui-build" ./tools/ci/compile_ci.sh
+    # e2e only needs the build; skip all QA checks (they run in the qa_check job) so it can build with -T1C
+    - script: SKIP_QA_CHECKS=true MVN_COMPILE_THREADS=1C ${{parameters.environment}} PROFILE="$PROFILE -Pskip-webui-build" ./tools/ci/compile_ci.sh
       displayName: Build Flink
       condition: not(eq(variables['SKIP'], '1'))
     - script: ${{parameters.environment}} FLINK_DIR=`pwd`/build-target ./tools/ci/uploading_watchdog.sh flink-end-to-end-tests/run-nightly-tests.sh ${{parameters.group}}
diff --git a/tools/azure-pipelines/jobs-template.yml b/tools/azure-pipelines/jobs-template.yml
index d86b5210465ed..bdba9e4b2a282 100644
--- a/tools/azure-pipelines/jobs-template.yml
+++ b/tools/azure-pipelines/jobs-template.yml
@@ -36,6 +36,8 @@ jobs:
     # See also https://docs.microsoft.com/en-us/azure/devops/pipelines/process/phases?view=azure-devops&tabs=yaml#workspace
 
   steps:
+  - script: ./tools/ci/print_machine_info.sh
+    displayName: Machine info
   # if on Azure, free up disk space
   - script: ./tools/ci/free_disk_space.sh
     target: host
@@ -67,8 +69,11 @@ jobs:
       echo "##vso[task.setvariable variable=PATH]$JAVA_HOME_${{parameters.jdk}}_X64/bin:$PATH"
     displayName: "Set JDK"
   # Compile
+  # SKIP_QA_CHECKS skips all QA checks (javadoc/scala/shaded/bundled/license); they run in the
+  # dedicated qa_check job. This lets the compile build run fast and multi-threaded (-T1C), off the
+  # test critical path.
   - script: |
-      ${{parameters.environment}} ./tools/ci/compile_ci.sh || exit $?
+      SKIP_QA_CHECKS=true MVN_COMPILE_THREADS=1C ${{parameters.environment}} ./tools/ci/compile_ci.sh || exit $?
       ./tools/ci/create_build_artifact.sh
     displayName: Compile
 
@@ -78,6 +83,59 @@ jobs:
       targetPath: $(FLINK_ARTIFACT_DIR)
       artifact: FlinkCompileArtifact-${{parameters.stage_name}}
 
+  # upload the installed Flink jars (run-scoped, NOT cached) so test jobs can reuse them and skip rebuild
+  - task: PublishPipelineArtifact@1
+    inputs:
+      targetPath: $(MAVEN_CACHE_FOLDER)/org/apache/flink
+      artifact: FlinkMavenRepoArtifact-${{parameters.stage_name}}
+
+  # build outputs that reuse stages read from target/ dirs (not .m2): the assembled dist (build-target)
+  # and flink-python/target (pyflink's test classpath: test-dependencies, *-tests.jar, testDataStream.jar)
+  - task: PublishPipelineArtifact@1
+    inputs:
+      targetPath: flink-dist/target
+      artifact: FlinkDistArtifact-${{parameters.stage_name}}
+  - task: PublishPipelineArtifact@1
+    inputs:
+      targetPath: flink-python/target
+      artifact: FlinkPythonTargetArtifact-${{parameters.stage_name}}
+
+# All QA checks (javadoc/scala/shaded/bundled/license) run here: this job builds Flink from scratch
+# single-threaded and validates it. Runs as an independent job (in parallel with compile/test) so it
+# is off the test critical path.
+- job: qa_check_${{parameters.stage_name}}
+  # succeeded() is needed to allow job cancellation
+  condition: and(succeeded(), not(eq(variables['MODE'], 'e2e')))
+  pool: ${{parameters.test_pool_definition}}
+  container: ${{parameters.container}}
+  timeoutInMinutes: 240
+  cancelTimeoutInMinutes: 1
+  workspace:
+    clean: all
+  steps:
+  - script: ./tools/ci/print_machine_info.sh
+    displayName: Machine info
+  # if on Azure, free up disk space
+  - script: ./tools/ci/free_disk_space.sh
+    target: host
+    condition: not(eq('${{parameters.test_pool_definition.name}}', 'Default'))
+    displayName: Free up disk space
+  - task: Cache@2
+    inputs:
+      key: $(PIPELINE_START_YEAR) | $(CACHE_KEY)
+      restoreKeys: $(PIPELINE_START_YEAR) | $(CACHE_FALLBACK_KEY)
+      path: $(MAVEN_CACHE_FOLDER)
+    continueOnError: true # continue the build even if the cache fails.
+    condition: not(eq('${{parameters.test_pool_definition.name}}', 'Default'))
+    displayName: Cache Maven local repo
+  - script: |
+      echo "##vso[task.setvariable variable=JAVA_HOME]$JAVA_HOME_${{parameters.jdk}}_X64"
+      echo "##vso[task.setvariable variable=PATH]$JAVA_HOME_${{parameters.jdk}}_X64/bin:$PATH"
+    displayName: "Set JDK"
+  # Build from scratch single-threaded and run all QA checks (no SKIP_QA_CHECKS).
+  - script: ${{parameters.environment}} ./tools/ci/compile_ci.sh
+    displayName: QA checks
+
 - job: test_${{parameters.stage_name}}
   dependsOn: compile_${{parameters.stage_name}}
   condition: and(succeeded(), not(eq(variables['MODE'], 'e2e')))
@@ -88,20 +146,31 @@ jobs:
   workspace:
     clean: all
   strategy:
+    # reuseArtifacts: reuse the compile job's installed jars (skip Step 1) instead of a full rebuild.
+    # Only stages that resolve everything from .m2 can reuse; stages needing build outputs under module
+    # target/ dirs (python's test classpath, the assembled dist, cluster ITs) do a full rebuild.
     matrix:
       core:
         module: core
+        reuseArtifacts: 'true'
       python:
         module: python
+        reuseArtifacts: 'true'
       table:
         module: table
+        reuseArtifacts: 'true'
       connect:
         module: connect
+        reuseArtifacts: 'true'
       tests:
         module: tests
+        reuseArtifacts: 'false'
       misc:
         module: misc
+        reuseArtifacts: 'false'
   steps:
+  - script: ./tools/ci/print_machine_info.sh
+    displayName: Machine info
   # if on Azure, free up disk space
   - script: ./tools/ci/free_disk_space.sh
     target: host
@@ -133,6 +202,30 @@ jobs:
     condition: not(eq('${{parameters.test_pool_definition.name}}', 'Default'))
     displayName: Cache Maven local repo
 
+  # overlay the compile job's freshly-installed Flink jars (run-scoped, overrides the cache) when this
+  # stage reuses them. continueOnError so a missing/expired artifact falls back to a rebuild.
+  - task: DownloadPipelineArtifact@2
+    continueOnError: true
+    condition: and(succeeded(), eq(variables['reuseArtifacts'], 'true'))
+    inputs:
+      path: $(MAVEN_CACHE_FOLDER)/org/apache/flink
+      artifact: FlinkMavenRepoArtifact-${{parameters.stage_name}}
+
+  # python reuse also needs the assembled dist (build-target) and flink-python/target test artifacts,
+  # which pyflink reads from target/ dirs. continueOnError so a missing artifact falls back to a rebuild.
+  - task: DownloadPipelineArtifact@2
+    continueOnError: true
+    condition: and(succeeded(), eq(variables['reuseArtifacts'], 'true'), eq(variables['module'], 'python'))
+    inputs:
+      path: flink-dist/target
+      artifact: FlinkDistArtifact-${{parameters.stage_name}}
+  - task: DownloadPipelineArtifact@2
+    continueOnError: true
+    condition: and(succeeded(), eq(variables['reuseArtifacts'], 'true'), eq(variables['module'], 'python'))
+    inputs:
+      path: flink-python/target
+      artifact: FlinkPythonTargetArtifact-${{parameters.stage_name}}
+
   - task: Cache@2
     inputs:
       key: '"$(module)" | $(DOCKER_IMAGES_CACHE_KEY)'
@@ -155,8 +248,9 @@ jobs:
   - script: sudo sysctl -w kernel.core_pattern=core.%p
     displayName: Set coredump pattern
 
-  # Test
-  - script: ${{parameters.environment}} ./tools/ci/uploading_watchdog.sh ./tools/ci/test_controller.sh $(module)
+  # Test — reuse the handed-off jars on stages that can (see the matrix); test_controller.sh falls back
+  # to a full rebuild when reuse is off or the jars aren't present.
+  - script: REUSE_INSTALLED_ARTIFACTS=$(reuseArtifacts) ${{parameters.environment}} ./tools/ci/uploading_watchdog.sh ./tools/ci/test_controller.sh $(module)
     displayName: Test - $(module)
     env:
       IT_CASE_S3_BUCKET: $(SECRET_S3_BUCKET)
diff --git a/tools/ci/compile.sh b/tools/ci/compile.sh
index bdc53428fa6cb..cabfd45d4d035 100755
--- a/tools/ci/compile.sh
+++ b/tools/ci/compile.sh
@@ -49,6 +49,13 @@ rm -rf ${MVN_VALIDATION_DIR}
 source "${CI_DIR}/stage.sh"
 source "${CI_DIR}/shade.sh"
 
+# Sample host load (CPU %steal / disk util) during the build to detect agent contention; killed on exit.
+# Written to stdout (the job log) because compile/qa/e2e don't publish a debug-files artifact.
+chmod +x "${CI_DIR}/sample_load.sh" 2>/dev/null || true
+"${CI_DIR}/sample_load.sh" 5 /dev/stdout &
+LOAD_SAMPLER_PID=$!
+trap 'kill "$LOAD_SAMPLER_PID" 2>/dev/null' EXIT
+
 echo "Maven version:"
 $MVN -version
 
@@ -58,9 +65,24 @@ echo "==========================================================================
 
 EXIT_CODE=0
 
-# run with -T1 because our maven output parsers don't support multi-threaded builds
-$MVN clean deploy -DaltDeploymentRepository=validation_repository::default::file:$MVN_VALIDATION_DIR -Dflink.convergence.phase=install -Pcheck-convergence \
-    -Dmaven.javadoc.skip=true -U -DskipTests -Dorg.slf4j.simpleLogger.log.org.apache.maven.plugins.shade=DEBUG "${@}" -T1 | tee $MVN_CLEAN_COMPILE_OUT
+# QA builds add shade DEBUG output and deploy to a local repo for the license check; other builds build fast and only install
+if [[ "${SKIP_QA_CHECKS:-false}" != "true" ]]; then
+    BUILD_MODE_ARGS="-Dorg.slf4j.simpleLogger.log.org.apache.maven.plugins.shade=DEBUG"
+    DEPLOY_ARGS="deploy -DaltDeploymentRepository=validation_repository::default::file:$MVN_VALIDATION_DIR -Dflink.convergence.phase=install -Pcheck-convergence"
+else
+    # -Dflink.fsShade.skip=true drops the FS-plugin shade (gs/azure/s3/oss) off the compile critical
+    # path; those plugins aren't needed by the reuse consumers (connect re-shades, e2e rebuilds).
+    BUILD_MODE_ARGS="-Pfast -Dflink.fsShade.skip=true"
+    DEPLOY_ARGS="install"
+fi
+# Only force snapshot updates (-U) unless the global Maven options already disable them (--no-snapshot-updates)
+UPDATE_SNAPSHOTS_ARG="-U"
+if [[ "${MVN_GLOBAL_OPTIONS_WITHOUT_MIRROR}" == *"--no-snapshot-updates"* ]]; then
+    UPDATE_SNAPSHOTS_ARG=""
+fi
+# The bundled/license QA checks parse single-threaded output (-T1); QA-skipping builds may set MVN_COMPILE_THREADS (e.g. 1C)
+$MVN clean ${DEPLOY_ARGS} \
+    -Dmaven.javadoc.skip=true ${UPDATE_SNAPSHOTS_ARG} -DskipTests ${BUILD_MODE_ARGS} "${@}" -T${MVN_COMPILE_THREADS:-1} | tee $MVN_CLEAN_COMPILE_OUT
 
 EXIT_CODE=${PIPESTATUS[0]}
 
@@ -79,6 +101,9 @@ if [ $EXIT_CODE != 0 ]; then
     exit $EXIT_CODE
 fi
 
+# All QA checks run only in the dedicated QA job (and local runs); compile/e2e skip them via SKIP_QA_CHECKS
+if [[ "${SKIP_QA_CHECKS:-false}" != "true" ]]; then
+
 echo "============ Checking Javadocs ============"
 
 javadoc_output=/tmp/javadoc.out
@@ -94,10 +119,6 @@ if [ $EXIT_CODE != 0 ] ; then
   exit $EXIT_CODE
 fi
 
-echo "============ Checking bundled dependencies marked as optional ============"
-
-MVN=$MVN ${CI_DIR}/verify_bundled_optional.sh $MVN_CLEAN_COMPILE_OUT || exit $?
-
 echo "============ Checking scala suffixes ============"
 
 MVN=$MVN ${CI_DIR}/verify_scala_suffixes.sh || exit $?
@@ -111,10 +132,16 @@ EXIT_CODE=$(($EXIT_CODE+$?))
 check_shaded_artifacts_s3_fs presto
 EXIT_CODE=$(($EXIT_CODE+$?))
 
+echo "============ Checking bundled dependencies marked as optional ============"
+
+MVN=$MVN ${CI_DIR}/verify_bundled_optional.sh $MVN_CLEAN_COMPILE_OUT || exit $?
+
 echo "============ Run license check ============"
 
 find $MVN_VALIDATION_DIR
 MVN=$MVN ${CI_DIR}/license_check.sh $MVN_CLEAN_COMPILE_OUT $MVN_VALIDATION_DIR || exit $?
 
+fi
+
 exit $EXIT_CODE
 
diff --git a/tools/ci/print_machine_info.sh b/tools/ci/print_machine_info.sh
new file mode 100755
index 0000000000000..70e2e1ae08683
--- /dev/null
+++ b/tools/ci/print_machine_info.sh
@@ -0,0 +1,103 @@
+#!/usr/bin/env bash
+################################################################################
+#  Licensed to the Apache Software Foundation (ASF) under one
+#  or more contributor license agreements.  See the NOTICE file
+#  distributed with this work for additional information
+#  regarding copyright ownership.  The ASF licenses this file
+#  to you under the Apache License, Version 2.0 (the
+#  "License"); you may not use this file except in compliance
+#  with the License.  You may obtain a copy of the License at
+#
+#      http://www.apache.org/licenses/LICENSE-2.0
+#
+#  Unless required by applicable law or agreed to in writing, software
+#  distributed under the License is distributed on an "AS IS" BASIS,
+#  WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+#  See the License for the specific language governing permissions and
+# limitations under the License.
+################################################################################
+
+#
+# Prints the CPU, core count, memory and disk throughput of the machine running the job. Intended as
+# the first step of every CI job so build/test timings can be correlated with the hardware they ran on.
+#
+
+echo "=============================================================================="
+echo "Machine information"
+echo "=============================================================================="
+
+echo "---- CPU ----"
+if command -v lscpu >/dev/null 2>&1; then
+    lscpu | grep -E "^(Architecture|Model name|CPU\(s\)|Thread\(s\) per core|Core\(s\) per socket|Socket\(s\)):"
+elif [ -r /proc/cpuinfo ]; then
+    grep -E "^model name" /proc/cpuinfo | head -n 1
+else
+    sysctl -n machdep.cpu.brand_string 2>/dev/null || echo "CPU model: n/a"
+fi
+# getconf is portable (Linux + macOS); nproc additionally honours cgroup limits in containers
+echo "Logical cores available: $(nproc 2>/dev/null || getconf _NPROCESSORS_ONLN 2>/dev/null || echo 'n/a')"
+
+echo "---- Memory ----"
+if command -v free >/dev/null 2>&1; then
+    free -h
+elif [ -r /proc/meminfo ]; then
+    grep -E "^(MemTotal|MemAvailable):" /proc/meminfo
+else
+    mem_bytes=$(sysctl -n hw.memsize 2>/dev/null) && echo "MemTotal: $((mem_bytes / 1024 / 1024)) MB" || echo "Memory: n/a"
+fi
+
+echo "---- Disk (working dir: $(pwd)) ----"
+df -h . 2>/dev/null
+# filesystem type (Linux df supports -T; ignored elsewhere)
+df -T . 2>/dev/null | awk 'NR==2 {print "Filesystem type: " $2}'
+if command -v lsblk >/dev/null 2>&1; then
+    lsblk -d -o NAME,ROTA,SIZE,MODEL 2>/dev/null
+fi
+# Rough sequential write throughput incl. flush. O_DIRECT is often unsupported on overlayfs (CI runs in
+# containers), so use conv=fdatasync; fall back to non-GNU dd (e.g. macOS) which lacks that option.
+if command -v dd >/dev/null 2>&1; then
+    disk_probe="./.machine_info_disktest"
+    echo "Sequential write (1 GiB, incl. flush):"
+    probe_out=$(dd if=/dev/zero of="$disk_probe" bs=1M count=1024 conv=fdatasync 2>&1)
+    if [ $? -ne 0 ]; then
+        probe_out=$(dd if=/dev/zero of="$disk_probe" bs=1m count=1024 2>&1)
+    fi
+    echo "$probe_out" | tail -n 1
+    rm -f "$disk_probe"
+fi
+
+# Small-file / metadata I/O -- the workload maven-shade actually generates (unpack/repack thousands of
+# tiny class files). Sequential MB/s says nothing about this; a slow-IOPS disk shows up here, not above.
+# Zero deps: time creating then deleting many tiny files. GNU date gives ms; falls back to seconds*1000.
+now_ms() { local d; d=$(date +%s%3N 2>/dev/null); case "$d" in ''|*[!0-9]*) d=$(( $(date +%s) * 1000 ));; esac; echo "$d"; }
+iops_dir="./.machine_info_iops_$$"
+mkdir -p "$iops_dir" 2>/dev/null
+N=2000
+t0=$(now_ms); i=0
+while [ "$i" -lt "$N" ]; do printf 'x' > "$iops_dir/f$i"; i=$(( i + 1 )); done
+sync 2>/dev/null
+t1=$(now_ms)
+rm -rf "$iops_dir"
+t2=$(now_ms)
+cr=$(( t1 - t0 )); [ "$cr" -le 0 ] && cr=1
+dl=$(( t2 - t1 )); [ "$dl" -lt 0 ] && dl=0
+echo "Small-file I/O: create ${N} tiny files in ${cr} ms ($(( N * 1000 / cr )) files/s), delete in ${dl} ms"
+
+# tmpfs availability -- can we put the (IOPS-heavy) build I/O in RAM to dodge a slow disk?
+echo "---- tmpfs availability ----"
+echo "/dev/shm: $(df -h /dev/shm 2>/dev/null | awk 'NR==2{print $2" total, "$4" free"}' || echo 'n/a')"
+RAMDIR="${TMPFS_BUILD_DIR:-/mnt/ram}"
+if [ -d "$RAMDIR" ] && : > "$RAMDIR/.mi_wtest" 2>/dev/null; then
+    rm -f "$RAMDIR/.mi_wtest"
+    echo "$RAMDIR: PRESENT & writable (fs=$(df -T "$RAMDIR" 2>/dev/null | awk 'NR==2{print $2}'), size=$(df -h "$RAMDIR" 2>/dev/null | awk 'NR==2{print $2}'))"
+else
+    tdir=$(mktemp -d 2>/dev/null || echo /tmp/.mi_mnt); mkdir -p "$tdir" 2>/dev/null
+    if mount -t tmpfs -o size=8m tmpfs "$tdir" 2>/dev/null; then
+        echo "$RAMDIR: absent, but in-job 'mount -t tmpfs' is ALLOWED"; umount "$tdir" 2>/dev/null
+    elif sudo -n mount -t tmpfs -o size=8m tmpfs "$tdir" 2>/dev/null; then
+        echo "$RAMDIR: absent, but 'sudo mount -t tmpfs' is ALLOWED"; sudo -n umount "$tdir" 2>/dev/null
+    else
+        echo "$RAMDIR: absent and no tmpfs-mount privilege -> add container '--tmpfs $RAMDIR', or use /dev/shm"
+    fi
+    rmdir "$tdir" 2>/dev/null
+fi
diff --git a/tools/ci/sample_load.sh b/tools/ci/sample_load.sh
new file mode 100755
index 0000000000000..ecfa279e5f07a
--- /dev/null
+++ b/tools/ci/sample_load.sh
@@ -0,0 +1,81 @@
+#!/usr/bin/env bash
+################################################################################
+#  Licensed to the Apache Software Foundation (ASF) under one
+#  or more contributor license agreements.  See the NOTICE file
+#  distributed with this work for additional information
+#  regarding copyright ownership.  The ASF licenses this file
+#  to you under the Apache License, Version 2.0 (the
+#  "License"); you may not use this file except in compliance
+#  with the License.  You may obtain a copy of the License at
+#
+#      http://www.apache.org/licenses/LICENSE-2.0
+#
+#  Unless required by applicable law or agreed to in writing, software
+#  distributed under the License is distributed on an "AS IS" BASIS,
+#  WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+#  See the License for the specific language governing permissions and
+# limitations under the License.
+################################################################################
+
+#
+# Samples host load every INTERVAL seconds until killed, to detect contention on shared agents.
+# Zero dependencies (reads /proc). The key metric is CPU %steal: time this vCPU was runnable but the
+# hypervisor gave the physical core to another tenant -> the direct signal of an oversubscribed host.
+# Also reports %busy, %iowait, an approximate primary-disk util%, and loadavg vs core count.
+#
+# Usage: sample_load.sh [interval_seconds] [output_file]
+#
+
+INTERVAL="${1:-5}"
+OUT="${2:-/dev/stdout}"
+
+# Direct all output at the target. For a real file, reopen fd 1 once (works even when backgrounded).
+# For stdout keep the inherited fd: reopening /dev/stdout by path fails with ENXIO when this runs in
+# the background and stdout is a pipe.
+case "$OUT" in
+    ""|"-"|/dev/stdout|/dev/fd/1) : ;;
+    *) exec >> "$OUT" 2>&1 ;;
+esac
+
+if [ ! -r /proc/stat ]; then
+    echo "sample_load: /proc/stat not readable (not Linux?); skipping."
+    exit 0
+fi
+
+# cpu line fields after 'cpu': user nice system idle iowait irq softirq steal
+read_cpu() { awk '/^cpu /{print $2,$3,$4,$5,$6,$7,$8,$9}' /proc/stat; }
+# sum of io_ticks (ms spent doing I/O, field 13) over whole block devices (not partitions).
+# printf "%.0f" (not "print s+0") so large sums are plain integers, not awk scientific notation
+# (e.g. 3.431e+09), which bash arithmetic cannot parse.
+read_io() { awk '$3 ~ /^(sd[a-z]+|vd[a-z]+|xvd[a-z]+|nvme[0-9]+n[0-9]+)$/ {s+=$13} END{printf "%.0f\n", s+0}' /proc/diskstats; }
+
+ncpu=$(nproc 2>/dev/null || getconf _NPROCESSORS_ONLN 2>/dev/null || echo 1)
+prev_cpu=($(read_cpu)); prev_io=$(read_io); prev_io=${prev_io:-0}
+echo "# sample_load interval=${INTERVAL}s cores=${ncpu} -- watch 'steal' (>0 => contended host)"
+
+while :; do
+    sleep "$INTERVAL"
+    cur_cpu=($(read_cpu)); cur_io=$(read_io); cur_io=${cur_io:-0}
+    total=0
+    for i in 0 1 2 3 4 5 6 7; do
+        d[$i]=$(( ${cur_cpu[$i]} - ${prev_cpu[$i]} ))
+        total=$(( total + ${d[$i]} ))
+    done
+    [ "$total" -le 0 ] && total=1
+    idle=$(( ${d[3]} + ${d[4]} ))                 # idle + iowait
+    busy=$(( 100 * (total - idle) / total ))
+    iowait=$(( 100 * ${d[4]} / total ))
+    steal=$(( 100 * ${d[7]} / total ))
+    # io_ticks delta (ms) over the interval (INTERVAL*1000 ms) -> util%. Guard so a bad read can't
+    # abort the whole sample line.
+    util=0
+    case "$cur_io$prev_io" in
+        *[!0-9]*) : ;;
+        *) util=$(( (cur_io - prev_io) / (INTERVAL * 10) )) ;;
+    esac
+    [ "$util" -gt 100 ] && util=100
+    load=$(cut -d' ' -f1 /proc/loadavg)
+    printf '%s busy=%3d%% iowait=%3d%% steal=%3d%% disk_util=%3d%% load=%s/%s\n' \
+        "$(date +%T)" "$busy" "$iowait" "$steal" "$util" "$load" "$ncpu"
+    prev_cpu=("${cur_cpu[@]}"); prev_io=$cur_io
+done
diff --git a/tools/ci/test_controller.sh b/tools/ci/test_controller.sh
index 0a620fb6f5cc9..91bd8f4b59305 100755
--- a/tools/ci/test_controller.sh
+++ b/tools/ci/test_controller.sh
@@ -73,6 +73,13 @@ export WATCHDOG_ADDITIONAL_MONITORING_FILES="$DEBUG_FILES_OUTPUT_DIR/mvn-*.log"
 
 source "${HERE}/watchdog.sh"
 
+# Sample host load (CPU %steal, iowait, disk util) during the whole build+test, to measure whether the
+# agent is contended. Output goes to the debug-files artifact; the sampler is killed when this exits.
+chmod +x "${HERE}/sample_load.sh" 2>/dev/null || true
+"${HERE}/sample_load.sh" 5 "$DEBUG_FILES_OUTPUT_DIR/load-sample.log" &
+LOAD_SAMPLER_PID=$!
+trap 'kill "$LOAD_SAMPLER_PID" 2>/dev/null' EXIT
+
 # =============================================================================
 # Step 1: Rebuild jars and install Flink to local maven repository
 # =============================================================================
@@ -81,12 +88,34 @@ export LOG4J_PROPERTIES=${HERE}/log4j.properties
 MVN_LOGGING_OPTIONS="-Dlog.dir=${DEBUG_FILES_OUTPUT_DIR} -Dlog4j.configurationFile=file://$LOG4J_PROPERTIES"
 
 MVN_COMMON_OPTIONS="-Dfast -Pskip-webui-build $MVN_LOGGING_OPTIONS"
-MVN_COMPILE_OPTIONS="-DskipTests"
-MVN_COMPILE_MODULES=$(get_compile_modules_for_stage ${STAGE})
-
 CALLBACK_ON_TIMEOUT="print_stacktraces | tee ${DEBUG_FILES_OUTPUT_DIR}/jps-traces.out"
-run_with_watchdog "run_mvn $MVN_COMMON_OPTIONS $MVN_COMPILE_OPTIONS $PROFILE $MVN_COMPILE_MODULES install" $CALLBACK_ON_TIMEOUT
-EXIT_CODE=$?
+
+# Reuse the jars the compile job handed off (REUSE_INSTALLED_ARTIFACTS + jars actually present) and skip
+# the rebuild. Only stages that resolve everything from .m2 can do this; stages needing build outputs
+# under module target/ dirs (e.g. python's test classpath, the assembled dist) must do a full rebuild.
+# Fall back to a full rebuild if no jars are present (e.g. an isolated retry after the artifact expired).
+FLINK_INSTALLED_JARS_DIR="${MAVEN_CACHE_FOLDER:-$HOME/.m2/repository}/org/apache/flink"
+if [[ "${REUSE_INSTALLED_ARTIFACTS:-false}" == "true" && -d "$FLINK_INSTALLED_JARS_DIR" && -n "$(ls -A "$FLINK_INSTALLED_JARS_DIR" 2>/dev/null)" ]]; then
+	echo "Reusing jars installed by the compile job; skipping rebuild/install."
+	# relink build-target when a prebuilt distribution was handed off (e.g. the python stage)
+	if [ ! -e build-target ]; then
+		dist_dir=$(ls -d flink-dist/target/flink-*-bin/flink-* 2>/dev/null | head -n 1)
+		if [ -n "$dist_dir" ]; then
+			ln -sfn "$dist_dir" build-target
+			echo "Linked build-target -> $dist_dir"
+		fi
+	fi
+	EXIT_CODE=0
+else
+	if [[ "${REUSE_INSTALLED_ARTIFACTS:-false}" == "true" ]]; then
+		echo "REUSE_INSTALLED_ARTIFACTS set but no handed-off jars in ${FLINK_INSTALLED_JARS_DIR}; doing a full rebuild."
+	fi
+	MVN_COMPILE_OPTIONS="-DskipTests"
+	MVN_COMPILE_MODULES=$(get_compile_modules_for_stage ${STAGE})
+	# the install step is a -DskipTests build (no test-output log parsing here), so it can run multi-threaded
+	run_with_watchdog "run_mvn $MVN_COMMON_OPTIONS $MVN_COMPILE_OPTIONS $PROFILE $MVN_COMPILE_MODULES -T${MVN_COMPILE_THREADS:-1C} install" $CALLBACK_ON_TIMEOUT
+	EXIT_CODE=$?
+fi
 
 if [ $EXIT_CODE != 0 ]; then
 	echo "=============================================================================="