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RequestState: “Queued for Predicate Disk”Īnother way to examine performance is to list the Cell metrics that are gathered automatically byt the cell using “ cellcli“. To see the IO occurring from the cell log in to the “ cellcli” utility on a cell and use the “list activerequest” command to see active IOs on the cell as follows: W.total_waits, w.time_waited, w.average_waitįROM V$SYSTEM_EVENT w, V$ASM_DISK d, V$CELL c To see the waits for the instance since startup use the following: W.p1 = c.cell_hashval AND w.p2 = d.hash_value SELECT w.event, c.cell_path, d.name, w.p3 To see if any sessions are currently waiting, and for which cell: To see if an instance has waited on these events, how often and for how long one may use queries which exploit the following Exadata Cell v$views:
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Just looking at the list is an indication of the types of offloads that may occur and for which a process may wait and this includes table scans, index fast full scans, file creation and RMAN smart Backup and restore. There are currently 8 cell oriented wait events for which an Oracle process may wait as follows: This measure the number of bytes that were offloaded over the Exadata iterconnect as a percentage of the nuber of bytes theoretcially eligible for predicate offload.Īnother way to examine the efficiency is to look at Cell Specific Wait events to see the type, frequency and average duration of the events. Select 100 – 100*s1.value/s2.value io_filtering_percentageĪnd n1.name = ‘cell physical IO interconnect bytes’Īnd n2.name = ‘cell physical IO bytes eligible for predicate offload’
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To determine offload benefit for SQL where clauses (filtering), Column Projections and Joins we use the “ cell physical IO interconnect bytes” and “ cell physical IO bytes eligible for predicate offload” statistics as follows: The Statistic “ cell physical IO bytes saved during optimized RMAN file restore” is an indication of RMAN benefits using Exadata. The Statistic “ cell physical IO bytes saved during optimized file creation” tells us how we have benefited using Exadata for Datafile create and extend. Here are the stats:Ĭell blocks helped by minscn optimizationĬell physical IO bytes eligible for predicate offloadĬell physical IO bytes saved during optimized RMAN file restoreĬell physical IO bytes saved during optimized file creationĬell simulated physical IO bytes eligible for predicate offloadĬell simulated physical IO bytes returned by predicate offload V$SYSSTAT lists 16 statistics involving cells and we can use some of them straight from the view and some require a calculation. Look at the total offload efficiency using system stats. To measure these activities there are several V$ Views and here are some of the ways one may view the benefit of these offloads:ġ.
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RMAN Fast Incremental Backups– When Block Change Tracking is used with RMAN and Exadata the Cell does the incremental backups at a granularity of the individual block, rather than at the granularity of a group of blocks as is done without Exadata. Likewise if a data file is added to a tablespace or a file is resized, or autoextends, then this is offloaded to the cells for formatting the blocks of the file reducing both IO and workload on the server.ĥ. Data File Creation or Extension formatting – When Create Tablespace DDL statements are issued a datafile is created. Certain Data Warehouse Joins – in this case a cell may join data from multiple tables that are joined in the downloaded SQL using the Bloom filtering technique to reduce the number of rows that are returned over the storage network to be post-processed back in the Oracle Database instance.Ĥ. Of course case 1 and 2 may be combined.ģ. Column Projections on SQL statements – in this case the column list is a subset of the columns of a table and the SQL is offloaded to the cell which reads the blocks and returns only the selected columns to the requesting host node. Filters or where clauses on SQL statements – in this case the SQL is offloaded to the cell which reads the blocks and applies the filters to the rows before returning the results over the Exadata Infiniband Storage Interconnect to the requesting host node.Ģ. More customers have begun to look at Exadata since the announcement last autumn and I have been teaching the Oracle Exadata Seminar this year to both an EMEA Audience and audiences in North America.Įxadata permits intelligent offloading of certain types of IO to the Cells where it is processed locally reducing the amount of traffic on the storage network and thereby reducing contention, latency and improving performance. Enter your email address to subscribe to this blog and receive notifications of new posts by email.