On 10/26/10 10:18 AM, Ozz Nixon wrote:
I am the only user on this system right now, and one table select count(*) took over 20 minutes:wikitags exists and has 58,988,656 records. Structure (in pascal) is: quer.SQL.Add('create table '+DBTags+' ('); quer.SQL.Add(' pagename '+SQL_TITLE+'(100) not null,'); quer.SQL.Add(' tagword '+SQL_TITLE+'(15) not null,'); quer.SQL.Add(' soundex2 '+SQL_TITLE+'(4) not null,'); quer.SQL.Add(' metaphone '+SQL_TITLE+'(15) not null,'); quer.SQL.Add(' metaphone2 '+SQL_TITLE+'(22) not null,'); quer.SQL.Add(' carverphone '+SQL_TITLE+'(22) not null,'); quer.SQL.Add(' instances '+SQL_INT32+' not null,'); if SQL_NAME_PRIMARY_KEYS then quer.SQL.Add(' constraint '+DBTags+'_PK'); quer.SQL.Add(' primary key(pagename, tagword, instances)'); quer.SQL.Add(')'); where SQL_TITLE = 'varchar', SQL_IN32 = 'int' I have hung off indexes for each column, to resolve my previous "performance" issue from 3+ weeks ago. However, COUNT() is still dog slow - this table is a write once, read many... *never* update, nor delete.
count(*) has to read the whole table to get the accurate count. The reason for this is that different clients can see different versions of that table, for instance, if client A is already in a transaction, and client B then does an INSERT, the two clients will see different values for the count.
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