Database Tuning - User and Rollback Data Spaces, Recovery, Backup ISYS366 – Week 5-6 Database Tuning - User and Rollback Data Spaces, Recovery, Backup 9/12/2018 ISYS366 - Week05

Database Deliverables of a System Development Process ERD Relational model Disk space requirements Tuning goals – response time, etc. Security requirements Data requirements Data entry and retrieval Backup and recovery Execution plans – EXPLAIN PLAN Acceptance testing 9/12/2018 ISYS366 - Week05

Disk Space Requirements – Sizing tables CREATE TABLE employee (…) TABLESPACE user_work PCTFREE 20 PCTUSED 60 STORAGE(INITIAL 10M NEXT 5K PCTINCREASE 0); 9/12/2018 ISYS366 - Week05

Disk Space Requirements – Sizing tables Blocks Block header = 90 bytes 2K block size: 2048-90 = 1958 bytes 4K block size: 4096-90 = 4006 bytes 9/12/2018 ISYS366 - Week05

Disk Space Requirements – Sizing tables Blocks Block header = 90 bytes 2K block size: 2048-90 = 1958 bytes 4K block size: 4096-90 = 4006 bytes pctfree the amount of space reserved in the block for updates that will expand the row the purpose is to minimize disk I/O by reducing row chaining and row migration row chaining occurs when you have to go to another block to get the rest of the row row migration occurs when you have to write a row to another data block (can be cause by too low pctfree) 9/12/2018 ISYS366 - Week05

Disk Space Requirements – Sizing tables pctfree used for both tables and indexes Default is 10% The more volatile you data, the higher pctfree For DW and OLAP, pctfree can be 0 1958*(10/100) = 196 bytes (round up) 9/12/2018 ISYS366 - Week05

Disk Space Requirements – Sizing tables pctused Determine when used blocks can be readded to the list of blocks into which rows can be added Default is 40, which is too low for frequent deletes For frequent deletes, try: 95 - pctfree 9/12/2018 ISYS366 - Week05

Disk Space Requirements – Sizing tables Free list space Each table has associated with it lists of data blocks that have been allocated for that table These lists contain free spaces for inserting rows called "free lists“ Blocks in the free list is less than PCTUSED full 2048 – 90 – 196 = 1762 bytes for data 9/12/2018 ISYS366 - Week05

Disk Space Requirements – Sizing tables Space used per row Bytes per row When data is available Average bytes per row SELECT AVG(NVL(VSIZE(col1),0)) + AVG(NVL(VSIZE(col2),0)) + AVG(NVL(VSIZE(col3),0)) + AVG(NVL(VSIZE(col4),0)) FROM table; 9/12/2018 ISYS366 - Week05

Disk Space Requirements – Sizing tables Space used per row When data is available Maximum bytes per row SELECT column_name, data_type, data_length FROM table WHERE table_name = 'table_name'; 3 bytes for row header 1 byte for each column 1 byte for each long column 10 bytes for each ROWID (Oracle 8) Rows per block Free space/bytes per row 9/12/2018 ISYS366 - Week05

Disk Space Requirements – Sizing tables Determining if pctfree is correct ANALYZE TABLE table COMPUTE STATISTICS; RETRIEVE DATA SELECT Num_rows, Blocks, Num_rows/Blocks FROM User_Tables WHERE Table_name = 'TABLE_NAME'; Perform an update Run ANALYZE again If the number of rows is fewer, then that means they have been moved to a new data block. Thus, the pctfree is NOT high enough. If, however, the Avg_space (also generated by ANALYZE) is large, then the pctfree is TOO high 9/12/2018 ISYS366 - Week05

Determining actual storage SELECT COUNT(*) FROM mytable; SELECT COUNT (DISTINCT (SUBSTR (ROWID, 1, 8)) || (SUBSTR (ROWID, 15,4))) FROM mytable; #rows per block = #rows/#blocks OR ANALYZE TABLE table COMPUTE STATISTICS; RETRIEVE DATA SELECT Num_rows, Blocks, Num_rows/Blocks FROM User_Tables WHERE Table_name = 'TABLE_NAME'; 9/12/2018 ISYS366 - Week05

Disk Space Requirements – Sizing indexes Blocks Block header = 161 bytes 2K block size: 2048-161 = 1887 bytes 4K block size: 4096-161 = 3935 bytes pctfree Same as for tables 9/12/2018 ISYS366 - Week05

Disk Space Requirements – Sizing indexes Space used per index row Average bytes per indexed column 8 bytes for index row header 1 byte for each column 1 byte for each long column 1 byte if index is UNIQUE 6-10 bytes for each ROWID (Oracle 8) Blocking Factor (rows per block) Free space/bytes per row 9/12/2018 ISYS366 - Week05

Disk Space Requirements – Sizing indexes N.B. deleted index space is rarely reused, so indexes may grow even if tables don't! 9/12/2018 ISYS366 - Week05

Sizing Tablespaces 9/12/2018 ISYS366 - Week05 SQL> select * From user_tablespaces; TABLESPACE_NAME INITIAL_EXTENT NEXT_EXTENT MIN_EXTENTS MAX_EXTENTS PCT_INCREASE --------------- -------------- ----------- ----------- ----------- ------------ MIN_EXTLEN STATUS CONTENTS LOGGING EXTENT_MAN ALLOCATIO ---------- --------- --------- --------- ---------- --------- SYSTEM 106496 106496 1 300 1 0 ONLINE PERMANENT LOGGING DICTIONARY USER RBS 1048576 1048576 2 121 0 USERS 57344 57344 1 121 1 TEMP 106496 106496 1 121 0 0 ONLINE TEMPORARY LOGGING DICTIONARY USER INDX 57344 57344 1 121 1 OEM_REPOSITORY 131072 131072 1 2.147E+09 0 131072 ONLINE PERMANENT LOGGING DICTIONARY USER DRSYS 40960 40960 1 505 50 WEBBOARD 40960 40960 1 505 50 8 rows selected. 9/12/2018 ISYS366 - Week05