Spring Batch Partition Threads Not Executing together - spring-batch

Question

We have spring batch job reading XML files and inserting to DB. Each batch slave partition is taking 10000 XML's and writing to DB.
Below is the Thread pool configuration
#Bean
public ThreadPoolTaskExecutor taskExecutor() {
ThreadPoolTaskExecutor taskExecutor = new ThreadPoolTaskExecutor();
taskExecutor.setMaxPoolSize(80);
taskExecutor.setCorePoolSize(50);
taskExecutor.setQueueCapacity(30);
taskExecutor.setWaitForTasksToCompleteOnShutdown(true);
taskExecutor.afterPropertiesSet();
return taskExecutor;
}
We are partitioning into 30 chunks and commit of 100 for each threads. All the 30 threads are inserting into table BATCH_STEP_EXECUTION says starting. Few completes in seconds with same number of records and others are waiting and takes 3 to 7 minutes. Application configuration is 6GB memory and Linux 64 bit having 96 CPU.
Server Configuration
Architecture: x86_64
CPU op-mode(s): 32-bit, 64-bit
Byte Order: Little Endian
CPU(s): 96
On-line CPU(s) list: 0-95
Thread(s) per core: 2
Core(s) per socket: 24
Socket(s): 2
NUMA node(s): 2
Vendor ID: GenuineIntel
CPU family: 6
Model: 85
Model name: Intel(R) Xeon(R) Platinum 8160M CPU # 2.10GHz
Stepping: 4