根據死鎖事件查看相應時間段的AWR，的確發現大量的分配事務槽等待
mos解釋如下：
CAUSE
By default the INITRANS value for a table is one, and for an index is two. This defines an internal block structure called the
Interested Transaction List (ITL). In order to modify data in a block, a process needs to use an empty ITL slot to record that the
transaction is interested in modifying some of the data in the block. If there are insufficient free ITL slots then new ones will be
taken in the free space reserved in the block. If this runs out and too many concurrent DML transactions are competing for the
same data block we observe contention against the following wait event - "enq: TX - allocate ITL entry".
You can see candidates for re-organisation due to ITL problems in the "Segments by ITL Waits" section of an Automatic
Workload Repository (AWR) report:
Segments by ITL Waits
* % of Capture shows % of ITL waits for each top segment compared
* with total ITL waits for all segments captured by the Snapshot
Owner Tablespace Name Object Name Subobject Name Obj. Type ITL Waits % of Capture
PIN BRM_TABLES SERVICE_T TABLE 188 84.30
PIN BRM_TABLES BILLINFO_T P_R_06202012 TABLE PARTITION 35 15.70
SOLUTION
The main solution to this issue is to increase the ITL capability of the table or index by re-creating it and altering the INITRANS or
PCTFREE parameter to be able to handle more concurrent transactions. This in turn will help to reduce "enq: TX - allocate ITL
entry" wait events.
To reduce enq: TX - allocate ITL entry" wait events, We need to follow the steps below:
Increase INITRANS
1) Depending on the number of transactions in the table we need to alter the value of INITRANS. here it has been changed to 50:
alter table <table name> INITRANS 50;
2) Then re-organize the table using move (alter table <table_name> move;)
3) Then rebuild all the indexes of this table as below
alter index <index_name> rebuild INITRANS 50;
Increase PCTFREE
If the issue is not resolved by increasing INITRANS then try increasing PCTFREE. Increasing PCTFREE holds more space back and
so spreads the same number of rows over more blocks. This means that there are more ITL slots available, overall.
1) Spreading rows into more number of blocks will also helps to reduce this wait event.
alter table <table name> PCTFREE 20;
2) Then re-organize the table using move (alter table service_T move;)
3) Rebuild index
alter index index_name rebuild PCTFREE 20;
A Combination of increasing both INITRANS and PCTFREE
1) Set INITRANS to 50 and pct_free to 40
alter table <table_name> PCTFREE 20 INITRANS 50;
2) Re-organize the table using move (alter table <table_name> move;)
3) Then rebuild all the indexes of the table as below
alter index <index_name> rebuild PCTFREE 20 INITRANS 50;
NOTE: The table/index can be altered to set the new value for INITRANS. But the altered value takes effect for new blocks
only. You need to rebuild the objects so that the blocks are initialized again.
For an index this means the index needs to be rebuild or recreated.
For a table this can be achieved through:
exp/imp
alter table move
dbms_redefenition