onstat -g scn Scan Information
The onstat -g scn command displays the status and detail of a current scan. This information can be used to determine how long a long-running scan will take to complete. For tables, the onstat -g scn command output identifies whether a scan is a light or bufferpool scan.
[Table Information]
Light Scan Info
descriptor address next_lpage next_ppage ppage_left bufcnt look_aside
RSAM batch sequential scan info
SesID Thread Partnum Rowid Rows Scan'd Scan Type Lock Mode Notes
2370448 2890168 200145 452909 87235 Light Table Look aside,
2370440 2890147 20013d 101 0 Buffpool +Test Must copy
[Index Information]
RSAM batch index scan info
SesID Thread Partnum Scan Type Lock Mode Notes
2370436 2890156 20019a SLock+Test
Start Key GT :-2147483648:
Stop Key EQ :1500:
Current key :170:
Current position: buffp 0x10a4bc0c8 pagenum 4 slot 11 rowoff 4 flags 0
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| Option | Description |
|---|---|
| descriptor (decimal) | Light scan ID |
| address (hex) | Memory address of the light scan descriptor |
| next_lpage (hex) | Next logical page address to scan |
| next_ppage (hex) | Next physical page address to scan |
| ppage_left (decimal) | Number of physical pages left to scan in the current extent |
| bufcnt | Number of light scan buffers used for this light scan |
| look_aside | Whether look aside is needed for this light scan (Y = yes, N = no). Look asides occur when a thread needs to examine the buffer pool for existing pages to obtain the latest image of a page being light scanned. |
| SesID | Session ID |
| Thread | Thread ID |
| Partnum | Partition number |
| Rowid | Current row ID |
| Rows Scan'd | Number of rows that have been scanned |
| Scan Type | For tables, either:
|
| Lock Mode | The type of acquired lock or no lock:
|
| Start key | Start key of the scan |
| Stop key | End key of the scan |
| Current key | The current key in the scan |
| Current position | The current location of the scan in the index, for example, the page, slot, and offset |
Notes
Look aside : The light scan is performing look aside.
The light scan reads blocks of pages directly from disk into large buffers, rather than getting each page from the buffer manager. In some cases, this process requires the light scan to check the buffer pool for the presence of each data page that it processes from one of its large buffers; this process is called look aside. If the page is currently in the buffer pool, the light scan will use that copy instead of the one in the light scan large buffer. If the page is not in the buffer pool, the light scan will use the copy that the light scan read from disk into its large buffer. If the light scan is performing look aside, the performance of the scan is slightly reduced.
In many cases, the light scan can detect that it is impossible for the buffer pool to have a newer version of the page. In these situations, the light scan will not check the buffer pool, and the look aside note will be absent.
Forward row lookup : The server is performing a light scan on a table that has rows that span pages. The light scan must access and use the buffer pool to get the remainder pieces of any rows that are not completely on the home page.
The light scan reads blocks of pages directly from disk into large buffers, rather than getting each page from the buffer manager. In some cases, this process requires the light scan to check the buffer pool for the presence of each data page that it processes from one of its large buffers; this process is called look aside. If the page is currently in the buffer pool, the light scan will use that copy instead of the one in the light scan large buffer. If the page is not in the buffer pool, the light scan will use the copy that the light scan read from disk into its large buffer. If the light scan is performing look aside, the performance of the scan is slightly reduced.
In many cases, the light scan can detect that it is impossible for the buffer pool to have a newer version of the page. In these situations, the light scan will not check the buffer pool, and the look aside note will be absent.
Forward row lookup : The server is performing a light scan on a table that has rows that span pages. The light scan must access and use the buffer pool to get the remainder pieces of any rows that are not completely on the home page.