How Can I Configure init_td

Transaction directory (TD) is a unique structure used by Ustore tables to store page transaction information. The number of TDs determines the maximum number of concurrent transactions supported on a page. When creating a table or index, you can specify the initial TD size init_td, whose default value is 4. That is, four concurrent transactions are supported to modify the page. The maximum value of init_td is 128.

You can configure init_td based on the service concurrency requirements. You can also determine whether to adjust it based on the occurrence frequency of "wait available td" events during service running. Generally, wait available td is 0. If the value of wait available td is not 0, the "wait available td" event exists. In this case, you are advised to increase the value of init_td and observe the event for several times. If this case occasionally occurs, you are advised not to adjust the value because the extra TD slots occupy more space. You are advised to gradually increase the value in ascending order, such as 8, 16, 32, 48, ..., and 128, and check whether the number of wait events decreases significantly in this process. Use the minimum value of init_td with few wait events as the default value to save space. wait available td is one of the values of wait_status. wait_status indicates the waiting status of the current thread, including the waiting status details. You can query the value of wait_status in the PG_THREAD_WAIT_STATUS view. The value none indicates that the system is not waiting for any event. If there is a wait event, you can view the value of wait available td. The following is an example. For details about init_td, see "SQL Reference > SQL Syntax > CREATE TABLE" in Developer Guide. To view and modify the value of init_td, perform the following steps:

gaussdb=# CREATE TABLE test1(name varchar) WITH(storage_type = ustore, init_td=2);
gaussdb=# \d+ test1
                              Table "public.test1"
 Column |       Type        | Modifiers | Storage  | Stats target | Description
--------+-------------------+-----------+----------+--------------+-------------
 name   | character varying |           | extended |              |
Has OIDs: no
Distribute By: HASH(a)
Location Nodes: ALL DATANODES
Options: orientation=row, storage_type=ustore, init_td=2, compression=no, segment=off, toast.storage_type=ustore, toast.toast_storage_type=enhanced_toast

gaussdb=# ALTER TABLE test1 SET(init_td=8);
gaussdb=# \d+ test1
                              Table "public.test1"
 Column |       Type        | Modifiers | Storage  | Stats target | Description
--------+-------------------+-----------+----------+--------------+-------------
 name   | character varying |           | extended |              |
Has OIDs: no
Distribute By: HASH(a)
Location Nodes: ALL DATANODES
Options: orientation=row, storage_type=ustore, compression=no, segment=off, init_td=8, toast.storage_type=ustore, toast.toast_storage_type=enhanced_toast

gaussdb=# SELECT * FROM pg_thread_wait_status;
 node_name | db_name  |           thread_name           |    query_id     |       tid       |    sessionid    | lwtid | psessionid | tlevel | smpid | wait_status | wait_event | locktag | lo
ckmode | block_sessionid | global_sessionid
-----------+----------+---------------------------------+-----------------+-----------------+-----------------+-------+------------+--------+-------+-------------+------------+---------+---
-------+-----------------+------------------
 sgnode    |          | PageWriter                      |               0 | 139769678919424 | 139769678919424 | 16915 |            |      0 |     0 | none        | none       |         |
       |                 | 0:0#0
 sgnode    |          | PageWriter                      |               0 | 139769736066816 | 139769736066816 | 16913 |            |      0 |     0 | none        | none       |         |
       |                 | 0:0#0
 sgnode    |          | PageWriter                      |               0 | 139769707755264 | 139769707755264 | 16914 |            |      0 |     0 | none        | none       |         |
       |                 | 0:0#0
 sgnode    |          | PageWriter                      |               0 | 139769761756928 | 139769761756928 | 16912 |            |      0 |     0 | none        | none       |         |
       |                 | 0:0#0
 sgnode    |          | PageWriter                      |               0 | 139769783772928 | 139769783772928 | 16911 |            |      0 |     0 | none        | none       |         |
       |                 | 0:0#0


gaussdb=# DROP TABLE test1;
DROP TABLE