Kbase 19063: What is the -rereadnolock parameter ?
| Autor |
Progress Software Corporation - Progress |
| Acesso |
Público |
| Publicação |
19/09/2008 |
|
Status: Verified
GOAL:
How does -rereadnolock startup client parameter change record locking?
GOAL:
What is the -rereadnolock parameter ?
GOAL:
What the -rereadnolock parameter does?
GOAL:
-rereadnolock Startup Parameter
FACT(s) (Environment):
All Supported Operating Systems
Progress 8.x
Progress 9.x
OpenEdge 10.x
FIX:
-rereadnolock Startup Parameter
This startup parameter changes the behavior of NO-LOCK record retrieval. It was introduced in 8.3B.
When a PROGRESS client (4GL, AppServer, web-agent) makes a request to find a record with NO-LOCK, it will not always get the newest copy of the record. If the record is already being used NO-LOCK by another 4GL buffer then the old copy usually remains in memory rather than replacing it with a new copy. This behavior is not always desirable.
The basic mechanism that accounts for this behavior works like this. PROGRESS first fetches the record from the database. PROGRESS then takes the ROWID of the record and compares it to the ROWIDs of records that are already in memory, in use by other 4GL buffers.
If the ROWID matches one of the records in memory, PROGRESS usually discards the new one, instead of the older record. This does not happen when the new record contains more information than the old one, for example, when the new record has more fields because it was based on a different field list.
The -rereadnolock startup parameter causes PROGRESS to discard the older record and replace it with the latest version. The following rules describe how this startup parameter interacts with related PROGRESS features:
-rereadnolock:
* affects the behavior of NO-LOCK record retrieval by FOR EACH or PRESELECT EACH.
* affects the behavior of NO-LOCK FINDs except for retrieval by RECID or ROWID as described below.
* does not affect the behavior of NO-LOCK FINDs based on retrieval by RECID or ROWID. PROGRESS immediately looks in memory for the record, and does not read a new record if there is a copy in memory.
* affects the behavior of retrieval on a NO-LOCK QUERY except for CACHEing and network PREFETCHing as described below.
* does not affect the behavior of a query cache. The DEFINE QUERY statement has an optional CACHE n phrase. Browsing a query uses a default cache of 20 records. This startup parameter does not cause the record to be re-read if it is in the cache.
* does not affect the behavior of a network PREFETCH cache. By default, OPEN QUERY across a network uses a prefetch buffer that may contain multiple records read-ahead by the server. This startup parameter does not cause the record to be re-read if it is in the cache. OPEN QUERY has a NO-PREFETCH option that eliminates this network cache.