| Monday, August 3, 2009 |
| Full Table Scans |
Full Table Scans
Here are some scripts related to Full Table Scans .
System Statistics (Table)SYSTEM STATISTICS (TABLE) NOTES:
Statistic Name - Name of the statistic
Bytes - Size
This query provides information on the full table scan activity. If your application is OLTP only, having long full table scans can be an indicator of having missing or incorrect indexes or untuned SQL.
Table fetch by rowid reflect the cumulative number of rows fetched from tables using a TABLE ACCESS BY ROWID operation.
Table fetch continued row reflect the cumulative number of continued rows fetched. This value is incremented when accessing a row that is longer than a block in length and when accessing "migrated" rows. Migrated rows are rows that were relocated from their original location to a new location because of an update that increased their size to the point where they could no longer be accommodated inside their original block. Access to migrated rows will cause this statistic's value to increment only if the access is performed by ROWID. Full table scans of tables that contain migrated rows do not cause this counter to increment.
Table scan blocks gotten reflect the cumulative number of blocks read for full table scans.
Table scans rows gotten reflect the cumulative number of rows read for full table scans.
Table scans (cache partitions) is used with the Parallel Query Option. The number of RowID ranges corresponds to the number of simultaneous query server processes that scan the table.
Table scans (long scans) indicate a full scan of a table that has > 5 database blocks.
Table scans (rowid ranges) is used with the Parallel Query Option. The number of RowID ranges corresponds to the number of simultaneous query server processes that scan the table.
Table scans (short scans) indicate a full scan of a table that has <= 5 database blocks.
select NAME,
VALUE
from v$sysstat
where NAME like '%table'
Process Table Scans
PROCESS TABLE SCAN NOTES:
User Process - Name of user process
Long Scans - Full scan of a table that has > 5 database blocks.
Short Scans - Full scan of a table that has <= 5 database blocks.
Row Retrieved - Cumulative number of rows read for full table scans.
select ss.username||'('||se.sid||') ' "User Process",
sum(decode(name,'table scans (short tables)',value)) "Short Scans",
sum(decode(name,'table scans (long tables)', value)) "Long Scans",
sum(decode(name,'table scan rows gotten',value)) "Rows Retreived"
from v$session ss,
v$sesstat se,
v$statname sn
where se.statistic# = sn.statistic#
and (name like '%table scans (short tables)%'
or name like '%table scans (long tables)%'
or name like '%table scan rows gotten%')
and se.sid = ss.sid
and ss.username is not null
group by ss.username||'('||se.sid||') '
Process Table Scans (Avg)
PROCESS TABLE SCAN (AVERAGE) NOTES:
User Process - Name of user process
Short Scans - Number of short scans (<= 5 blocks)
Long Scans - Number of long scans (> 5 blocks)
Rows Retrieved - Number of rows retrieved
Long Scans Length - Average long scan length (i.e. full table scan of > 5 blocks)
select ss.username||'('||se.sid||') ' "User Process",
sum(decode(name,'table scans (short tables)',value)) "Short Scans",
sum(decode(name,'table scans (long tables)', value)) "Long Scans",
sum(decode(name,'table scan rows gotten',value)) "Rows Retreived",
round((sum(decode(name,'table scan rows gotten',value)) - (sum(decode(name,'table scans (short tables)',value)) * 5)) / (sum(decode(name,'table scans (long tables)', value))),2) "Long Scans Length"
from v$session ss,
v$sesstat se,
v$statname sn
where se.statistic# = sn.statistic#
and (name like '%table scans (short tables)%'
or name like '%table scans (long tables)%'
or name like '%table scan rows gotten%')
and se.sid = ss.sid
and ss.username is not null
group by ss.username||'('||se.sid||') '
having sum(decode(name,'table scans (long tables)', value)) != 0
order by 3 descLabels: Full Table Scans |
posted by Srinivasan .R @ 11:15 PM  |
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