Spring Batch Paging Issue - spring

Question

I am working on Spring Batch and I am using paging for fetching data from DB. for the first time Its firing Query as expected but for second page its adding one more unexpected parameter. I don't understand why.
My Query in XML file is
<bean id="summaryAppReader" scope="step" autowire-candidate="false"
class="org.springframework.batch.item.database.JdbcPagingItemReader">
<property name="dataSource" ref="dataSource" />
<property name="rowMapper">
<bean class="com.majesco.nyl.batch.mapper.SummaryApplicationRowMapper" />
</property>
<property name="queryProvider">
<bean
class="org.springframework.batch.item.database.support.SqlPagingQueryProviderFactoryBean">
<property name="dataSource" ref="dataSource" />
<property name="fromClause" value="VIEW_SUMMARY_APPLICATION" />
<property name="selectClause"
value="application_id, upper(application_status) as application_status,relationship_code, create_date,submission_date,transmission_date,TRANSMISSION_STATUS,tpa_notes,site_details_id,transaction_num,PROCESS_STATUS,process_date,application_status_date,first_name,middle_name,last_name,suffix,prefix,APPROVED_REJECTED_DATE,action_by,ass_acronym,user_name,applicant_name,site_name,ASSOCIATION_ID, (TO_DATE('#{jobParameters['runDate']}', 'yyyy-mm-dd') - trunc(create_date)) as elapsedDays" />
<property name="sortKeys">
<map>
<entry key="transaction_num" value="ASCENDING" />
</map>
</property>
<property name="whereClause"
value="(upper(application_status)='PENDING' OR (upper(application_status) IN ('APPROVED','DECLINED') AND trunc(application_status_date) = TO_DATE('#{jobParameters['runDate']}', 'yyyy-mm-dd'))) and TRANSACTION_NUM >= :minId and TRANSACTION_NUM <= :maxId" />
</bean>
</property>
<property name="parameterValues">
<map>
<entry key="minId" value="#{stepExecutionContext[minValue]}" />
<entry key="maxId" value="#{stepExecutionContext[maxValue]}" />
</map>
</property>
</bean>
for fetching data for first page its firing query something like this and its expected
Reading page 0
SQL used for reading first page: [SELECT * FROM (SELECT application_id, upper(application_status) as application_status,relationship_code, create_date,submission_date,transmission_date,TRANSMISSION_STATUS,tpa_notes,site_details_id,transaction_num,PROCESS_STATUS,process_date,application_status_date,first_name,middle_name,last_name,suffix,prefix,APPROVED_REJECTED_DATE,action_by,ass_acronym,user_name,applicant_name,site_name,ASSOCIATION_ID, (TO_DATE('2016-06-29', 'yyyy-mm-dd') - trunc(create_date)) as elapsedDays FROM VIEW_SUMMARY_APPLICATION WHERE (upper(application_status)='PENDING' OR (upper(application_status) IN ('APPROVED','DECLINED') AND trunc(application_status_date) = TO_DATE('2016-06-29', 'yyyy-mm-dd'))) and TRANSACTION_NUM >= :minId and TRANSACTION_NUM <= :maxId ORDER BY transaction_num ASC) WHERE ROWNUM <= 10]
Using parameterMap:{minId=100000002630, maxId=100000002663}
But for the second page its adding one more parameter in Query _TRANSACTION_NUM which is unexpected like
Reading page 1
SQL used for reading remaining pages: [SELECT * FROM (SELECT application_id, upper(appication_status) as application_status,relationship_code, create_date,submission_date,transmission_date,TRANSMISSION_STATUS,tpa_notes,site_details_id,transaction_num,PROCESS_STATUS,process_date,application_status_date,first_name,middle_name,last_name,suffix,prefix,APPROVED_REJECTED_DATE,action_by,ass_acronym,user_name,applicant_name,site_name,ASSOCIATION_ID, (TO_DATE('2016-06-29', 'yyyy-mm-dd') - trunc(create_date)) as elapsedDays FROM VIEW_SUMMARY_APPLICATION WHERE (upper(application_status)='PENDING' OR (upper(application_status) IN ('APPROVED','DECLINED') AND trunc(application_status_date) = TO_DATE('2016-06-29', 'yyyy-mm-dd'))) and TRANSACTION_NUM >= :minId and TRANSACTION_NUM <= :maxId ORDER BY transaction_num ASC) WHERE ROWNUM <= 10 AND ((transaction_num > :_transaction_num))]
Using parameterMap:{minId=100000002596, maxId=100000002629, _transaction_num=100000002622}
FYI. TRANSACTION_NUM is not unique.

Answer 1

It's due to your sortKeys. You defined the following:
<property name="sortKeys">
<map>
<entry key="transaction_num" value="ASCENDING" />
</map>
</property>
Spring Batch is using the highest transaction_num from page 0 and saying the next page must have a transaction_num higher than that.
The framework will increment the bind variable with each page to ensure you keep getting unique results. The problem here is that you realistically need a Primary Key to page correctly otherwise your pageSize (default = 10 and seen where it adds WHERE ROWNUM <= 10 to your query) will cut off some of your records.