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bill-buchanbill-buchan
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Merge pull request #249 from ministryofjustice/DBA-658
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‎.github/workflows/oracle-db-delius-operational-artefacts.yml

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@@ -42,6 +42,13 @@ on:
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options:
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- "yes"
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- "no"
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DeployMVRefreshPurgeChildCursors:
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description: "Create Job to purge MV Refresh Child Cursors?"
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type: choice
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default: "no"
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options:
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- "yes"
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- "no"
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SourceCodeVersion:
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description: "Source version for the hmpps-delius-operation-automation. Enter a pull request, branch, commit ID, tag, or reference."
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type: string
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-e deploy_users=${{ github.event.inputs.DeployUsers }} \
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-e deploy_performance_test_users=${{ github.event.inputs.DeployPerformanceTestUsers }} \
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-e deploy_audit_stub_users=${{ github.event.inputs.DeployAuditStubUsers }} \
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-e deploy_plan_management=${{ github.event.inputs.DeployPlanManagement }}
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-e deploy_plan_management=${{ github.event.inputs.DeployPlanManagement }} \
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-e deploy_mv_refresh_purge_child=${{ github.event.inputs.DeployMVRefreshPurgeChildCursors }}

‎playbooks/delius-artefacts-playbook.yml

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include_role:
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name: "{{ playbook_dir }}/oracle_plan_management/install_plan_management_job"
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when: deploy_plan_management | default('no') == "yes"
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# Cursors created by Materialied View refreshes may not be shared due to their
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# use of Flashback Query. This results in a build up of large numbers of
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# versions of each refresh which cannot be shared and waste shared pool memory.
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# This job periodically detects such cursors and purges them.
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- name: Deploy MV Refresh Purge Child Cursors Job
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include_role:
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name: "{{ playbook_dir }}/oracle_mv_refresh_purge_child_cursors/oracle_mv_refresh_purge_child_cursors"
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when: deploy_mv_refresh_purge_child | default('no') == "yes"

‎playbooks/oracle_mv_refresh_purge_child_cursors/oracle_mv_refresh_purge_child_cursors/files/install_mv_refresh_purge_child_cursors_job.sh

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#!/bin/bash
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. ~/.bash_profile
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sqlplus -s / as sysdba <<EOF
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SET LINES 1000
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SET PAGES 0
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WHENEVER SQLERROR EXIT FAILURE
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GRANT EXECUTE ON dbms_shared_pool TO delius_user_support;
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GRANT SELECT ON sys.v_\$sqlarea TO delius_user_support;
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GRANT SELECT ON sys.v_\$sql_shared_cursor TO delius_user_support;
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SET SERVEROUT ON
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DECLARE
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l_owner CONSTANT VARCHAR2(128) := 'DELIUS_USER_SUPPORT';
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l_program_name CONSTANT VARCHAR2(128) := 'MV_REFRESH_PURGE_CHILD_CURSORS';
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l_job_name CONSTANT VARCHAR2(128) := l_program_name || '_JOB';
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BEGIN
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FOR x IN (SELECT job_name
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FROM dba_scheduler_jobs
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WHERE owner = l_owner
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AND job_name = l_job_name )
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LOOP
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DBMS_SCHEDULER.drop_job(
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job_name => l_owner || '.' || l_job_name
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);
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END LOOP;
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FOR x IN (SELECT program_name
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FROM dba_scheduler_programs
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WHERE owner = l_owner
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AND program_name = l_program_name )
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LOOP
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DBMS_SCHEDULER.drop_program(
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program_name => l_owner || '.' || l_program_name
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);
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END LOOP;
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DBMS_SCHEDULER.create_program (
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program_name => l_owner || '.' || l_program_name
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,program_type => 'PLSQL_BLOCK'
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,program_action => q'{
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DECLARE
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l_count INTEGER := 0;
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l_sharable_mem INTEGER := 0;
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BEGIN
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/*
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We identify cursors to purge by the following criteria:
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1. They contain an MV_REFRESH comment, and
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2. They are not sharable due to the use of Flashback, and
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3. They have a child version count above 5
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*/
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FOR x IN (
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SELECT
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sql_id,
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address,
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hash_value,
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sharable_mem,
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version_count
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FROM
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v\$sqlarea s
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WHERE
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upper(s.sql_text) LIKE '/* MV_REFRESH (MRG) */%'
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AND s.version_count > 5
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AND EXISTS (
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SELECT
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1
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FROM
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v\$sql_shared_cursor c
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WHERE
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c.sql_id = s.sql_id
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AND c.flashback_cursor = 'Y'
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)
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) LOOP
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sys.DBMS_SHARED_POOL.purge(x.address|| ','|| x.hash_value, 'C');
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l_count := l_count + x.version_count;
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l_sharable_mem := l_sharable_mem + x.sharable_mem;
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END LOOP;
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DBMS_OUTPUT.put_line('Purged '
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|| l_count
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|| ' unsharable cursors and released '
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|| round(l_sharable_mem / 1024 / 1024, 2)
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|| 'Mb of memory.');
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END;
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}'
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,enabled => TRUE
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,comments => 'See '||l_job_name||' comments.');
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DBMS_SCHEDULER.create_job(
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job_name => l_owner || '.' || l_job_name
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,program_name => l_owner || '.' || l_program_name
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,start_date => SYSTIMESTAMP
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,repeat_interval => 'FREQ=HOURLY;'
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,end_date => NULL
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,comments => 'Materialized View refresh cursors are not sharable as they use flashback query. '||
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'This means that regular MV refreshes will gradually consume a large amount of '||
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'shared pool memory but will never be reused. This job detects such cursors and '||
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'purges them to ensure this memory may be reallocated to other components.'
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,enabled => TRUE);
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END;
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/
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EXIT
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EOF

‎playbooks/oracle_mv_refresh_purge_child_cursors/oracle_mv_refresh_purge_child_cursors/tasks/main.yml

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---
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# When Materialized Views are refreshed this creates child SQL cursors which are not reusable
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# since they use Flashback Query. Since the refreshes happen frequently, the shared pool can
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# begin to fill up with hundreds of versions of the same refresh queries, which can occupy
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# considerable amounts of memory and deprive it from other components of the database.
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#
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# For details see: Using the Flashback Query Feature Results in a High Number of Child Cursors (Doc ID 2192862.1)
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#
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# An SR 3-35666063241 was raised with Oracle for this behaviour but has been closed on the
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# basis that it is expected for Materialized View refreshes.
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#
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# As a workaround we install a scheduler job to clean up the child cursors.
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# This job detects non-reusable materialized view refresh cursors and force purges them
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# from the shared pool to allow this memory to be reused.
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#
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- name: Install Materialized View Refresh Purge Child Cursors Job
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script: install_mv_refresh_purge_child_cursors_job.sh

‎playbooks/oracle_mv_refresh_purge_child_cursors/playbook.yml

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---
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- hosts: "{{ hosts }}"
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gather_facts: no
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become: yes
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become_user: oracle
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roles:
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- oracle_mv_refresh_purge_child_cursors

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