Temporary Indexes

[Bayron]

Hi everyone,
I have never used CDX indexes, and I want to use them now...

How good will it be to use the TEMPORARY ( or MEMORY ) clause, on this indexes, since some say that there are problems with index file corruption some times???

Will this clause prevent this problems???

I am sure It may give me more speed if they are run in memory... Are they???

[Enrico Maria Giordano]

I made some test in the past with TEMPORARY clause without noticed any speed differences.

EMG

[MarcoBoschi]

Read this
TEMPORARY
If this option is specified, a temporary index is created which is automatically destroyed when the index is closed. The temporary index may be created in memory only or in a temporary file. This lies in the responsibility of the RDD used for index creation.

My test in a LAN : non differences in elap time

Code: Select all  Expand view

ANNOUNCE RDDSYS

FUNCTION MAIN

USE i_201003
? seconds()
INDEX ON field->ref TAG REF TO marco
? seconds()

? seconds()
INDEX ON ref TAG REF TO marco temporary
? seconds()

RETURN NIL


               
INIT PROCEDURE RddInit
REQUEST DBFFPT
REQUEST DBFCDX
rddSetDefault( "DBFCDX" )
 

exactly the same time!
bye

[Maurizio]

Marco

have you tried

INDEX ON ref TAG REF TO TEMP TEMPORARY ?



Maurizio

[Enrico Maria Giordano]

Marco

have you tried

INDEX ON ref TAG REF TO TEMP TEMPORARY ?



Maurizio

Do you mean to remove FIELD from the key? I don't think it will make any difference.

EMG

[Maurizio]

Enrico

NO , change Marco with TEMP


INDEX ON field->ref TAG REF TO TEMP TEMPORARY ?

[MarcoBoschi]

Maurizio?
This test?

ANNOUNCE RDDSYS

FUNCTION MAIN


USE i_201003

GO TOP
? seconds()
INDEX ON ref TAG REF TO TEMP TEMPORARY
? seconds()


GO TOP
? seconds()
INDEX ON field->ref TAG REF TO marco
? seconds()


RETURN NIL



INIT PROCEDURE RddInit
REQUEST DBFFPT
REQUEST DBFCDX
rddSetDefault( "DBFCDX" )

[Maurizio]

Marco

I remember reading that :

GO TOP
? seconds()
INDEX ON field->ref TAG REF TO TEMP TEMPORARY
? seconds()

This writes the file in PC memory

-----------------------------------------------------------------------

GO TOP
? seconds()
INDEX ON field->ref TAG REF TO marco TEMPORARY
? seconds()

This writes the file to hard disk
---------------------------------------------------------------------
Maurizio

[Enrico Maria Giordano]

TEMP or marco for the index filename does not make any difference. The TEMPORARY clause only makes the difference.

EMG

[Bayron]

I can imagine not making any difference in time, and even making everything a little slower, because of having to create indexes every time, but,

Can it make any difference in data consistency, and prevent data corruption????

[Enrico Maria Giordano]

Probably yes, but keep in mind that they are temporary indexes so you can't use them for the normal persistent indexes.

EMG

[stefano]

I’ve found an improvement using INDEX TEMP FOR … (xbrowse). Instead of SET FILTER... in LAN

Stefano

[Rick Lipkin]

Bayron

I have never used the TEMP option .. I kinda like to know where my files are being created, their names either .idx or .cdx.

Please consider this code ..

Code: Select all  Expand view

// this needs to be in your main.prg
REQUEST DBFCDX
rddsetdefault( "DBFCDX" )


Local FundDbf,dbf_stru

// create a temp file name off the root of the Default Folder

xVol := set(7)

DO WHILE .T.

   FundDbf := "TEMP"+(SUBSTR(TIME(),7,2)+SUBSTR(TIME(),4,2))+".DBF"
   IF .not. FILE( xVOL+"\DBTMP\"+FUNDDBF )
      EXIT
   ENDIF

ENDDO

DBF_STRU := { }
AADD( DBF_STRU, { "DESC",     "C",  40, 0 } )
AADD( DBF_STRU, { "AMOUNT",   "N",  8,  2 } )
AADD( DBF_STRU, { "FUNDED",   "N",  8,  2 } )
AADD( DBF_STRU, { "BOX",      "N",  2,  0 } )
AADD( DBF_STRU, { "CLASCODE", "C",  10, 0 } )

DBCREATE( xVOL+"\DBTMP\"+FUNDDBF, DBF_STRU )

SELECT 9
Use ( xVOL+"\DBTMP\"+FUNDDBF ) via "DBFCDX" EXCL
      Index on ClasCode Tag ClasCode        // creates .cdx of the same database name
ELSE
   CLose Databases
   RETURN(.F.)
ENDIF

..
do your own data processing here
..

Close Databases
Ferase( "Tempxxxx.Dbf" )
Ferase( "Tempxxxx.Cdx" )

 

Note that if you use .cdx the name of the file is created for you ( same name as the .dbf) with a .cdx extention. If you use .Idx .. you have to create a separate index name for each index .. .cdx is the way to go because you can build multiple ( tags ) indexes into the same .cdx.

Rick Lipkin

[Enrico Maria Giordano]

TEMP is not an option, it's a filename.

EMG

[Bayron]

Thanks all for your comments...

I think that as Enrico said, Temporary indexes are good, but not for all situations...

My program does not use quite extensive Indexed databases... so I think I will go with creating permanent Indexes once per day, per week or so...

This kind of threads help us all to understand some attributes of FiveWin//(x)Harbour...

Thanks again...