9/11/2015ISYS366 - Week051 ISYS366 – Week 5-6 Database Tuning - User and Rollback Data Spaces, Recovery, Backup

9/11/2015ISYS366 - Week052 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

9/11/2015ISYS366 - Week053 Disk Space Requirements – Sizing tables CREATE TABLE employee (…) TABLESPACE user_work PCTFREE 20 PCTUSED 60 STORAGE(INITIAL 10M NEXT 5K PCTINCREASE 0);

9/11/2015ISYS366 - Week054 Disk Space Requirements – Sizing tables Blocks Block header = 90 bytes 2K block size: = 1958 bytes 4K block size: = 4006 bytes

9/11/2015ISYS366 - Week055 Disk Space Requirements – Sizing tables Blocks Block header = 90 bytes 2K block size: = 1958 bytes 4K block size: = 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)

9/11/2015ISYS366 - Week056 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 *(10/100) = 196 bytes (round up)

9/11/2015ISYS366 - Week057 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

9/11/2015ISYS366 - Week058 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

9/11/2015ISYS366 - Week059 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;

9/11/2015ISYS366 - Week0510 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

9/11/2015ISYS366 - Week0511 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

9/11/2015ISYS366 - Week0512 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';

9/11/2015ISYS366 - Week0513 Disk Space Requirements – Sizing indexes Blocks Block header = 161 bytes 2K block size: = 1887 bytes 4K block size: = 3935 bytes pctfree Same as for tables

9/11/2015ISYS366 - Week0514 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

9/11/2015ISYS366 - Week0515 Disk Space Requirements – Sizing indexes N.B. deleted index space is rarely reused, so indexes may grow even if tables don't!

9/11/2015ISYS366 - Week0516 Sizing Tablespaces 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 ONLINE PERMANENT LOGGING DICTIONARY USER RBS ONLINE PERMANENT LOGGING DICTIONARY USER USERS ONLINE PERMANENT LOGGING DICTIONARY USER TEMP ONLINE TEMPORARY LOGGING DICTIONARY USER INDX ONLINE PERMANENT LOGGING DICTIONARY USER OEM_REPOSITORY E ONLINE PERMANENT LOGGING DICTIONARY USER DRSYS ONLINE PERMANENT LOGGING DICTIONARY USER WEBBOARD ONLINE PERMANENT LOGGING DICTIONARY USER 8 rows selected.