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MSSM is the legacy implementation in Oracle. It has been around for many years, over many versions. ASSM was first introduced in Oracle9i Release 1 and its design intention was to eliminate the need to fine tune the myriad parameters used to control space allocation and provide high concurrency. For example, by having the FREELISTS parameter set to the default of 1, you might find that your insert/update intensive segments may be suffering from contention on free space allocation. When Oracle goes to insert a row into a table, update an index key entry, or update a row causing the row to migrate (more on that in a moment), it may need to get a block from the list of free blocks associated with the segment. If there is only one list, only one transaction at a time may review and modify this list they would have to wait for each other. Multiple FREELISTS and FREELIST GROUPS serve the purpose of increasing concurrency in such a case, as the transactions may each be looking at different lists and not contending with each other. When I discuss the storage settings shortly, I will mention which are for manual and which are for automatic segment space management, but in the area of storage/segment characteristics, the only storage settings that apply to ASSM segments are as follows: BUFFER_POOL PCTFREE INITRANS MAXTRANS (only in 9i; in 10g and above this is ignored for all segments)

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ID ASSIGN Expr { WHILE Expr DO Stmt { BEGIN StmtList END { IF Expr THEN Stmt { IF Expr THEN Stmt ELSE Stmt { PRINT Expr {

The remaining storage and physical attribute parameters do not apply to ASSM segments. Segment space management is an attribute inherited from the tablespace in which a segment is contained (and segments never span tablespaces). For a segment to use ASSM, it would have to reside in a tablespace that supported that method of space management.

This is a term used with table segments stored in the database. If you envision a table, for example, as a flat structure or as a series of blocks laid one after the other in a line from left to right, the high-water mark (HWM) would be the rightmost block that ever contained data, as illustrated in Figure 10-1.

Assign ($1, $3) } While ($2, $4) } Seq (List.rev $2) } IfThen ($2, $4) } IfThenElse ($2, $4, $6) } Print $2 }

Figure 10-1 Depiction of an HWM Figure 10-1 shows that the HWM starts at the first block of a newly created table As data is placed into the table over time and more blocks get used, the HWM rises If we delete some (or even all) of the rows in the table, we might have many blocks that no longer contain data, but they are still under the HWM, and they will remain under the HWM until the object is rebuilt, truncated, or shrunk (shrinking of a segment is a new Oracle 10g feature that is supported only if the segment is in an ASSM tablespace) The HWM is relevant since Oracle will scan all blocks under the HWM, even when they contain no data, during a full scan This will impact the performance of a full scan especially if most of the blocks under the HWM are empty.

To see this, just create a table with 1,000,000 rows (or create any table with a large number of rows), and then execute a SELECT COUNT(*) from this table Now, DELETE every row in it and you will find that the SELECT COUNT(*) takes just as long (or longer, if you need to clean out the block! Refer to the Block Cleanout section of 9 Redo and Undo to count 0 rows as it did to count 1,000,000 This is because Oracle is busy reading all of the blocks below the HWM to see if they contain data You should compare this to what happens if you used TRUNCATE on the table instead of deleting each individual row TRUNCATE will reset the HWM of a table back to zero and will truncate the associated indexes on the table as well.

You can generate the parser by calling fsyacc: fsyacc kittyParser.fsy This produces kittyParser.fs, which contains the implementations of the parser, along with a signature file kittyParser.fsi. The generated parser has one entry point for each %start symbol (here there is only one). The type of this entry point is as follows:

If you plan on deleting every row in a table, TRUNCATE if it can be used would be the method of choice for this reason In an MSSM tablespace, segments have a definite HWM In an ASSM tablespace, however, there is an HWM and a low HWM In MSSM, when the HWM is advanced (eg, as rows are inserted), all of the blocks are formatted and valid, and Oracle can read them safely With ASSM, however, when the HWM is advanced Oracle doesn t format all of the blocks immediately they are only formatted and made safe to read upon their first actual use The first actual use will be when the database decides to insert a record into a given block.