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$PREFETCHOFF

Ends pre-fetching of globals.

Synopsis

$PREFETCHOFF(gref,gref2)

Parameters

Argument Description
gref Optional — A global reference.
gref2 Optional — A global reference used to establish a range.

Description

$PREFETCHOFF turns off the pre-fetching of global nodes established by $PREFETCHON.

There are three forms of $PREFETCHOFF:

  • $PREFETCHOFF() turns off all pre-fetching established for the current process.

  • $PREFETCHOFF(gref) turns off pre-fetching of the gref node and all of its descendents. The gref value must correspond exactly to the $PREFETCHON value.

  • $PREFETCHOFF(gref,gref2) turns off pre-fetching of the nodes in the range gref through gref2. gref and gref2 must be nodes of the same global. The gref and gref2 values must correspond exactly to the $PREFETCHON values. You cannot turn off part of a range of values.

Upon successful completion, $PREFETCHOFF() returns 0. It returns 0 even if there were no pre-fetches to turn off.

Upon successful completion, $PREFETCHOFF(gref) and $PREFETCHOFF(gref,gref2) return a string of six integers separated by commas. These six values are: number of blocks prefetched, number of I/Os performed, number of prefetch operations, milliseconds of prefetch disk time, background job: number of blocks prefetched, and background job: number of I/Os performed.

Upon failure, all forms of $PREFETCHOFF return -1. $PREFETCHOFF(gref) and $PREFETCHOFF(gref,gref2) return -1 if there is no corresponding $PREFETCHON that exactly matches the specified global or range of globals, or if the specified prefetch global or range of globals has already been turned off.

Parameters

gref

A global reference, either a global or a process-private global. The global does not need to be defined at the time that the pre-fetch is turned off.

You can specify this global using @ indirection. Refer to Indirection in Using Caché ObjectScript.

You cannot specify a structured system variable name (SSVN) for this parameter.

gref2

A global reference used to establish a range with gref. Therefore, gref2 must be a global node lower in the same global tree as gref.

You can specify this global using @ indirection. Refer to Indirection in Using Caché ObjectScript.

Examples

The following example establishes two pre-fetches, then turns them off individually:

  SET ret=$PREFETCHON(^a)
  IF ret=1 { WRITE !,"prefetch established" }
  ELSE { WRITE !,"prefetch not established" }
  SET ret2=$PREFETCHON(^b)
  IF ret2=1 { WRITE !,"prefetch established" }
  ELSE { WRITE !,"prefetch not established" }
  SET retoff=$PREFETCHOFF(^a)
  IF retoff'=-1 { WRITE !,"prefetch turned off. Values:",retoff }
  ELSE { WRITE !,"prefetch not turned off" }
  SET retoff2=$PREFETCHOFF(^b)
  IF retoff2'=-1 { WRITE !,"prefetch turned off. Values:",retoff2 }
  ELSE { WRITE !,"prefetch not turned off" }
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The following example establishes two pre-fetches, then turns off all pre-fetches for the current process:

  SET ret=$PREFETCHON(^a)
  IF ret=1 { WRITE !,"prefetch established" }
  ELSE { WRITE !,"prefetch not established" }
  SET ret2=$PREFETCHON(^b)
  IF ret2=1 { WRITE !,"prefetch established" }
  ELSE { WRITE !,"prefetch not established" }
  SET retoff=$PREFETCHOFF()
  IF retoff=0 { WRITE !,"all prefetches turned off" }
  ELSE { WRITE !,"prefetch not turned off" }
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See Also