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<http://www.nntp.hk/web/?server=devzone.advantagedatabase.com>or if works http://www.nntp.hk/web/head,devzone.advantagedatabase.com,Advantage.xHarbour.html 2009/10/28 Mindaugas Kavaliauskas <dbto...@dbtopas.lt>: > Hi, > > > in the beginning I was going to write a private email to Przemek and ask > about CDX detail, but more deep test gave me an answer. > > The problem of the customers was that sometimes browse does not show records > (in scoped alias), but records for sure exist in database. We found that > ORDKEYCOUNT() return zero but scope is not empty. The problem of ADS RDD is > that it does not check return values of ADS API functions in many places, > for exmaple, in processing of DBOI_KEYCOUNT. Here AdsGetRecordCount() return > error 7022. > > Advantage Error Guide: > ---------------------- > 7022 Maximum index levels > > Problem: The current index is unbalanced. This problem is most likely to > occur when using very long index keys and new keys are being added to the > index. This error could also occur if the index is corrupt. > > Solution: Reindex the file. The reindexed file will be built using the > minimum number of levels. This will speed up all future operations using the > index. If this does not resolve the problem, reindex with a larger page size > (see Index Page Size, or see the API AdsReindex61 in the Advantage Client > Engine Help or the method AdsIndexPageSize in the Advantage TDataSet > Descendant Help). With a larger index page size, more keys will be stored in > each page and will thus reduce the number of levels required. For specific > equations showing the correlation between key and page size, see Index Key > Size and Page Size Relationships. > ---------------------- > > Unfortunately CDX page size is fixed 512 and can not be changed. I have a > database table from our customers. It has 50342 records only and index key > length is 133 bytes. I have a feeling this is a too small limits for real > life a database. Documented maximum key length is 240 bytes. > > I had an idea that index tree level count can be limited by CDX structure, > but after I've wrote a self contained test and compared ADSCDX and DBFCDX > results, I understand it is a limit of ADS implementation. Both my real life > key length 133, and a maximum documented key length 240 was tested (see test > source below): > RDD: ADSCDX KeyLen: 240 LASTREC(): 6058 ORDKEYCOUNT(): 0 > RDD: ADSCDX KeyLen: 133 LASTREC(): 250052 ORDKEYCOUNT(): 0 > So, using a maximum documented key length (240 bytes) ADS can manage tables > having only(!) 6058 records. The same results are for both 8.1 and 9.1 > version of ADS. > > (512-some_header) / (240 + pointer_size) = 2 keys per page > log(6058)/log(2+1)~= 7,927 ~= 8 > > (512-some_header) / (133 + pointer_size) = 3 keys per page > log(250052)/log(3+1)~= 8,966 ~= 9 > > So, maximum index tree level in ADS is 8, or 9, or a little more, if index > is unbalanced. Perhaps ADS uses a fixed length array to store pages in index > navigation operations. I've not tested yet, if DBSKIP() or DBSEEK() has also > the same limits, or it is a problem of ORDKEYCOUNT() only. > > I was unable to find a index level limit in Harbour's DBFCDX driver using > the test. > > > Regards, > Mindaugas > > > --------------------------- > #include "ads.ch" > > EXTERNAL ADS, DBFCDX > ANNOUNCE RDDSYS > > #define KEYLEN 240 > > FUNC main() > ADSSetFileType(ADS_CDX) > ADSSetServerType(ADS_REMOTE_SERVER) > ? "Press ESC to cancel" > test("ADSCDX", "\\server\share\test176", KEYLEN) > test("DBFCDX", "test176", KEYLEN) > RETURN 0 > > PROC test(cRDD, cPath, nKeyLen) > LOCAL nI, nJ > DBCREATE(cPath, {{"KEY", "C", nKeyLen, 0}}, cRDD, .T., "test") > ORDCREATE(cPath, "key", "KEY") > ? "Testing ", cRDD, "..." > FOR nI := 1 TO 1000 > FOR nJ := 1 TO 1000 > DBAPPEND() > FIELD->KEY := REPLICATE(HB_MD5(STR(nI) + STR(nJ)), 8) > NEXT > IF ORDKEYCOUNT() != LASTREC() > ? "RDD:", cRDD, "KeyLen:", nKeyLen, "LASTREC():", LASTREC(), > "ORDKEYCOUNT():", ORDKEYCOUNT() > EXIT > ENDIF > ?? nI > IF INKEY() == 27 > EXIT > ENDIF > NEXT > DBCLOSEAREA() > RETURN > > _______________________________________________ > Harbour mailing list > Harbour@harbour-project.org > http://lists.harbour-project.org/mailman/listinfo/harbour > -- Massimo Belgrano
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