diff --git a/datasets/add_months.sh b/datasets/add_months.sh
index 8f331c7..3c745dc 100755
--- a/datasets/add_months.sh
+++ b/datasets/add_months.sh
@@ -109,15 +109,31 @@ parallel --joblog add_months_joblog.txt --results add_months_logs \
 
 source "$SPARK_CONF_DIR/spark-env.sh"
 export PYSPARK_PYTHON="$PYTHON"
+
+# Compute executor resources from what spark-env.sh detected.
+# One executor gets all worker cores and ~85% of worker memory (leaving
+# headroom for the driver and overhead).
+_EXEC_CORES=${SPARK_WORKER_CORES:-$(nproc)}
+_WORKER_MEM_GB=${SPARK_WORKER_MEMORY%g}
+_EXEC_MEM_GB=$(( _WORKER_MEM_GB * 85 / 100 ))
+_DRIVER_MEM_GB=$(( _WORKER_MEM_GB * 10 / 100 ))
+SPARK_SUBMIT_CONF=(
+    --conf "spark.executor.cores=${_EXEC_CORES}"
+    --conf "spark.executor.memory=${_EXEC_MEM_GB}g"
+    --conf "spark.driver.memory=${_DRIVER_MEM_GB}g"
+)
+
 start_spark_cluster.sh
 
 spark-submit --master "spark://$(hostname):$SPARK_MASTER_PORT" \
+    "${SPARK_SUBMIT_CONF[@]}" \
     comments_part2.py \
     --indir="$TEMP_COMMENTS" \
     --out_by_subreddit="$STAGING_COMMENTS_SUB" \
     --out_by_author="$STAGING_COMMENTS_AUTH"
 
 spark-submit --master "spark://$(hostname):$SPARK_MASTER_PORT" \
+    "${SPARK_SUBMIT_CONF[@]}" \
     submissions_part2.py \
     --indir="$TEMP_SUBMISSIONS" \
     --out_by_subreddit="$STAGING_SUBMISSIONS_SUB" \