2953:BDE: Writing Buffer to Disk
KEYWORDS: BDE BUFFERED DBISAVECHANGES DBIUSEIDLETIME DATABASE AREA: Database P
Product: Delphi and the Borland Database Engine
Number: ?????
Versions: 1.x, 2.x
OS: WINDOWS 3.x, WINDOWS 95, WINDOWS NT
DATE: December 7, 1995
TITLE: Using DbiUseIdleTime and DbiSaveChanges.
General:
=======
Changes made to a table are not written directly to disk until
the table is closed. A power failure or system crash can
result in a loss of data, and an inconvenience. To avoid this
loss of data, two direct Database Engine calls can be made,
both of which have the similar effects. These functions are
DbiUseIdleTime and DbiSaveChanges.
DbiSaveChanges(hDBICur):
=======================
DbiSaveChanges saves to disk all the updates that are in the
buffer of the table associated with the cursor (hDBICur). It
can be called at any point. For example, one may want to make
save changes to disk every time a record is updated (add
dbiProcs to uses clause):
procedure TForm1.Table1AfterPost(DataSet: TDataSet);
begin
DbiSaveChanges(Table1.handle);
end;
This way, one does not have to worry about losing data if a
power failure or system crash occurs after a record update.
DbiSaveChanges can also be used to make a temporary table
(created by DbiCreateTempTable) permanent.
This function does NOT apply to SQL tables.
DbiUseIdleTime:
==============
DbiUseIdleTime can be called when the "Windows Message Queue"
is empty. It allows the Database Engine to save "dirty buffers"
to disk. In other words, it does what DbiSaveChanges does, but
performs the operation on ALL the tables that have been
updated. This operation however, will not necessarily occur
after every record update, because it can only be executed when
there is an idle period.
In Delphi, it can be used in this fashion (add dbiProcs to uses clause):
procedure TForm1.FormCreate(Sender: TObject);
begin
Application.onIdle := UseIdle;
end;
procedure Tform1.UseIdle(Sender: TObject; var Done: Boolean);
begin
DbiUseIdleTime;
end;
USAGE NOTES:
===========
Using both DbiUseIdleTime and DbiSaveChanges (after every
record modification) is redundant and will result in
unnecessary function calls. If the application is one that
perfroms a great deal of record insertions or modifications in
a small period of time, it is recommended that the client
either call DbiUseIdleTime during an idle period, or call
DbiSaveChanges after a group of updates.
If not very many updates are being performed on the table, the
client may choose to call DbiSaveChanges after every post or
set up a timer and call DbiUseIdleTime when a timer even is generated.
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