Optimización de consultas locales en bases de datos distribuidas
Tenses demonstrate the time of actions centered around the subject of the sentence. These actions are called verbs and change according to tenses.
Hernández Zúñiga Daniel
Parte del conjunto de optimización de consultas
There are four Past tenses:
- Past Simple
- Past Continuous
- Past Perfect Simple
- Past Perfect Continuous
Hasta este momento, se pueden eligir los algoritmos para realizar las operaciones relacionales.
Past Continuous is used for:
- an action that happened before another action in the past
- an action that started in the past and continued up to a given time in the past
- an action done several times up to a point in the past and continued to do after that point
- an action that happened in the past but is important at the time of reporting
Some adverbs used with Past Continuous:
- always, only, never, ever, still, just
Es la ultima capa que se efectúa en todos los nodos con fragmentos involucrados en la consulta
Past simple expresses:
- an action that happened in the past and has no connection with the present
- an action that happened once in the past
- an action that happened regularly in the past
- an action that was true for some time in the past
- an event or action that already occurred
- an action that is finite - has both a starting and a stopping point
Some adverbs used with Past Simple:
- yesterday
- last month, last year
- ago (e.g. two days ago)
- in (e.g. in 1997)
- never, always, seldom, often, frequently, occasionally, once, twice
Cada subconsulta que se ejecuta en un nodo, llamada consulta local, es optimizada usando el
esquema local del nodo.
Structure:
Did + subject + Base Form of the Verb?
e.g. Where did you meet her?
Optimización
Estrategias usuales de los optimizadores
Optimización SQL basa en estimaciones
Optimización heurística
-Cambia la consulta original por otra equivalente.
-Forma de minimizar los resultados intermedios
-Se basa en aplicar equivalencia de los operadores del algebra relacional
Proceso detallado de optimización
El optimizador crea un plan de ejecución eficaz para el estado de la base de datos
cada vez que se ejecuta la instrucción.
El optimizador de consultas debe analizar los planes posibles y elegir el de menor
costo estimado.
El optimizador de consultas de SQL ser ver es un optimizador basado en el costo
Funciona
There are four Present tenses:
- Present Simple
- Present Continuous
- Present Perfect
- Present Perfect Continuous
En una máquina que no se tenga que conectar al servidor a otras máquinas para efectuar
la consulta.
Present Continuous is used to indicate the ongoing time (now).
Some adverbs used with Present Continuous:
- now, right now
- at this moment
- at the moment
- continually
- perpetually
- this year
- this season
- forever
Para procesar una consulta local solo se hace referencia a tablas y bases de datos locales
dentro de la misma instancia del manejador de bases de datos.
Present Simple is used for:
- habits
- general truths
- repeated actions of events
- fixed arrangements/timetables
- feelings/opinions/beliefs
- instructions.
Some adverbs used with Present Simple:
- always
- usually
- seldom
- never
- sometimes
- often
- frequently, generally
- habitually, occasionally
- once, twice
