Annexe1: Valeurs mesurées pendant l'exécution d'une requête
Parmi les valeurs mesurées, nous considérons uniquement le nombre de consistent gets, sans prendre en compte les autres valeurs, car consistent gets est représentatif du nombre de pages disque lues (dans un état froid de la base, lorsque toute les données sont sur disque et que le cache est vide).
Les principales valeurs mesurées sont:
Statistics
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*db block gets : Number of times a CURRENT block was requested
*consistent gets : Number of times a consistent read was requested for a block.
*physical reads : Total number of data blocks read from disk. This number equals the value of "physical reads direct" plus all reads into buffer cache.
- redo size : Total amount of redo generated in bytes.
- sorts (disk) : Number of sort operations that required at least one disk write. Sorts that require I/O to disk are quite resource intensive. Try increasing the size of the initialization parameter SORT_AREA_SIZE. For more information, see "SORT_AREA_SIZE".
- sorts (memory) : Number of sort operations that were performed completely in memory and did not require any disk writes. You cannot do much better than memory sorts, except maybe no sorts at all. Sorting is usually caused by selection criteria specifications within table join SQL operations.
- rows processed: result cardinality
Annexe2, retour au TME LesJointures