Oracle Rdb Space Management

Transcription

1 Oracle Rdb Space Management Norman Lastovica Oracle Rdb Egnineering November 13, 06

2 Agenda Data Structures Mixed vs uniform storage areas Logical areas AIP, ABM, SPAM Algorithms Free space search (inserts) Implications 2

3 Logical Area Virtual container for data & indices Single logical area reside in single physical area Partitioned tables or indices have multiple logical areas; one for each partition Described by AIP data structure 3

4 AIP Entries Contains information specific to logical area Including area type List in RDB$SYSTEM area Searched sequentially, usually by logical area number In 7.2, AIP entry is cached in lock value block first time it is read 4

5 Dump of AIP Entry $ RMU/DUMP/LAREA=RDB$AIP RDB_RANDOM$DB A 005F first area bitmap page logical area 114, physical area 18 0A 0067 area name length 10 bytes F444E45565F4C4C area name 'ALL_VENDOR...' area name '...' snaps enabled TSN 34 01AE 008B record length 430 bytes In use Type Logical Area ABM D entry resides on page entry is in use MBZ '..' thresholds are (0,0,0) MBZ '.' record type btree index MBZ '.' Physical Area Length Name 5

6 Mixed vs Uniform Storage Areas In uniform area, clumps of pages are allocated to specific logical area In mixed area rows from multiple logical areas may reside on same page Mixed areas typically used for hash index access & clustered data 6

7 Storage Management Structures Mixed Format Storage Area Rdb System Area AIP AIP AIP AIP Storage Area 1 SPAM Data Data Data Data SPAM Data SPAM interval Storage Area 2 SPAM Data Data Data Data SPAM Data SPAM interval 7

8 Uniform Areas ABM Pages Bitmap indicating what SPAM page intervals contain data for logical area Only used for uniform areas No mechanism to add additional ABM pages to ABM chain; only one clump used If ABM clump is full storage area <area> is full error signaled Likely only possible with very small page size 8

9 Storage Management Structures Uniform Format Storage Area Rdb System Area AIP AIP AIP AIP SPAM Data ABM Data Data SPAM ABM SPAM interval Storage Area 9

10 Dump of ABM Highest bit $ RMU/DUMP/AREA=18/START=74/END=76 RDB_RANDOM$DB... First SPAM interval has pages for larea B 0016 next area bitmap page A max set bit index E MBZ '...' 00001E bitvector count 7776 Bits on this page bitvector '...' bitvector '...' :::: (58 duplicate lines) E6 bitvector '...' ABM is for larea F2 MBZ '...' F6 bitmap page for logical area

11 SPAM Pages SPAM page represents data pages from current SPAM to next SPAM SPAM interval For mixed areas SPAM simply shows fullness of pages in interval For uniform areas SPAM shows fullness & also owning logical area for each clump in interval SPAM interval may be increased for mixed areas 11

12 Dump of SPAM Uniform Area $ RMU/DUMP/AREA=18/START=1/END=1 RDB_RANDOM$DB FFFFFFFFF FFFFFFFFF 0016 pages 2-20: threshold 3 pages 21-25: threshold 0 Two bits for each threshold page 26: threshold 3 pages 27-37: threshold 0 pages 38-55: threshold 3 pages 56-63: threshold 0 page 64: threshold 3. page 65: threshold 0.. Pages for index ALL_VENDOR These pages have space These pages are full Clump count C7 153 clumps 006B 02C9 pages 2-19, logical area B 02CB pages 20-37, logical area E 02CD pages 38-55, logical area E 02CF pages 56-73, logical area D1 pages 74-91, logical area D3 pages , logical area

13 Thresholds Thresholds provide rough indication of how much space available on page Value 3 indicates page is not a candidate for storage; 0 thru 2 indicate degrees of not full Specified threshold levels, as percentage of available space, determine which level is set in SPAM 13

14 Thresholds Mixed Area $ RMU/DUMP/HEADER/OPTION=DEBUG MF_PERSONNEL... Storage area "DEPARTMENTS... - Thresholds are 70%, 85%, and 95%... MAX_FREE_LEN = 964. MAX_NEW_SEG_LEN = 956. MAX_PNO = 404. SPAM_T1 = 674. SPAM_T2 = 818. SPAM_T3 = 914. SPREAD_FLG = 01 STAREA_NAME = "DEPARTMENTS" THRESHOLD = (70., 85., 95.) SPAM_T% Byte counts based on threshold % of MAX_FREE_LEN 14

15 Thresholds Uniform Area Thresholds may be specified in CREATE STORAGE MAP statement If no thresholds specified in storage map then threshold byte counts calculated using area s MAX_FREE_LEN & AIP s REC_LEN Thresholds may be incorrect if columns added to or removed from the table Used space includes data & page overhead (LDX/TDX) 15

16 PGSPAMENT Errors If SPAM threshold value doesn t match actual fullness value of page then PGSPAMENT or PGSPMCLST error will be reported by RMU/VERIFY: %RMU-W-PGSPAMENT, area ORDER_AREA, page 6047 the fullness value for this data page does not match the threshold value in the space management page expected: 3, computed: 0 Can happen if SPAM flushed before data page & then process fails See Restrictions in Rdb Release Notes 16

17 PGSPAMENT Errors Can be corrected by: RMU/UNLOAD, recreate table, RMU/LOAD EXPORT/IMPORT BACKUP/RESTORE (doesn t correct AIP) RMU/REPAIR/LAREA & RMU/REPAIR/SPAM 17

18 18 Finding Free Space

19 Find Good Page Uniform Area - Overview SPAM Larea 1 Larea 1 Larea 1 Larea 3 Larea 3 Larea 3 Larea 2 Larea 2 Larea 2 Larea 1 Larea 1 Larea 1 empty empty empty 1. Assume that rows have been deleted & space is available in currently allocated pages 2. Using thresholds in SPAM pages, try to find free space in clumps currently allocated to logical area 3. If no room in existing clumps - allocate new clump 19

20 Find Good Page Uniform Area Scan First time insert is done: 1.ABM clump fetched 2.Each SPAM interval referenced by ABM is scanned looking for clump assigned to logical area that has enough free space Chosen location is noted in target page (TAR_PNO) for that logical area Subsequent inserts use TAR_PNO as starting point when searching for free space 20

21 Find Good Page Uniform Area Use Last Prior to 7.2 TAR_PNO is attach specific In 7.2 TAR_PNO is visible to all users on node When row is deleted, if page is less than current TAR_PNO, then TAR_PNO is set to page that had row deleted If no free space is found then logical area has new clump allocated 21

22 Find Good Page Uniform Area New Clump Search for free space starts in SPAM interval used by that attach for last clump allocated to any logical area in storage area If this is first clump to be allocated then start at beginning of area The area is searched from SPAM interval to end of storage area If no free space is found storage area is extended 22

23 Bulk Insert SPAM Contention When inserting into uniform area all inserters will attempt to insert into same pages at same time. Those users will have lock conflicts on SPAM pages & constantly have to bounce SPAM page off disk to one another Before Rdb 7.2, less lock conflicts but space usage wasn t as good; deletes not seen by other processes 7.2 biased toward efficient space usage but has more lock conflicts 23

24 Insert 1,000,000 Rows Seconds Users 24

25 Find Good Page Mixed Area Objective is to store on or near target page Starting target page is often based on hashed page number used for PLACEMENT VIA If no target page provided then: Start with TAR_PNO for logical area If no TAR_PNO then start with most recently referenced page in buffer pool If no pages in pool - start at beginning of area 25

26 26 Find Good Page Mixed Area have a starting page; see if there is space If start page has room then use it Otherwise, if TAR_PNO provided, look at other pages in same buffer If pages in buffer full, search SPAM interval If SPAM interval full, try next SPAM interval; wrap around to start of area if necessary If no space found anywhere then extend area Note: if extents are enabled then don t wait for locks on SPAM pages

27 Discarded Pages Node: RANDM4 (1/1/1) Oracle Rdb V Perf. Monitor 18-APR :43:54.44 Rate: 3.00 Seconds Logical Area Overview (Tables) Elapsed: 01:41:47.98 Page: 1 of 1 $1$DGA57:[RDB_RANDOM.RDB_RANDOM_MO_12_R1]RNDDB.RDB;1 Mode: Online Logical.Area.Name... record fetch record store record erase discarded CurTot ORDER_REC.ORDER1_ARE ORDER_REC.ORDER2_ARE ORDER_ITEM_REC.ORDER ORDER_ITEM_REC.ORDER WORK_ORDER_REC.MANUF WORK_ITEM_REC.MANUFA JOB_TICKET_REC.MANUF rows stored 7487 discarded pages 27

28 Discarded Pages Excessive Page Checking See Guide to Database Performance and Tuning section Recognizing Poor Insert Performance Caused by Excessive Page Checking AIP Length Problems in Indexes That Allow Duplicates AIP Length Problems in Segmented Strings Using DBKEY SCOPE IS ATTACH Clause 28

29 29 Storage systems Explained

30 metalink.oracle.com Q U E S T I O N S & 30 A N S W E R S