NexusDB Pty Ltd

Dataset component to create in-memory tables

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Purpose

TnxMemTable is a component for people that expect to have a TDataSet,

set it's FieldDefs and IndexDefs, call Open, be able to use it... Call

close and expect the memory to be freed. TnxMemTable is basically a

TnxTable that, on open, automatically creates a table in the "database

specific in-memory table" scope based on the FieldDefs (or on the

persistent field objects which are used to create the FieldDefs if

Fields have been defined but no FieldDefs). When you close the component

again that table is being deleted. If you don't specific a "TableName"

property an unique tablename is internally chosen for you. If a

TableName is specified it must be a unique name within the context of

that TnxDatabase. As long as the TnxMemTable is open you can access that

table from other TnxTable's or TnxQuery's under that name.

One thing that's important to mention. In-memory tables always "live"

wherever the "Buffer Manager" is (TnxServerEngine). A TnxRemoteServerEngine does not

contain a Buffer Manager. It's simply a proxy that turns method calls

into messages to be send over the transport which then get turned back

from messages to method calls on the TnxServerEngine by the command

handler in the server. That means if you are creating an in-memory

table, either direct or using the TnxMemTable, if the TnxDatabase is

connected to a TnxSession which in turn is connected to a

TnxRemoteServerEngine, then the table will exist inside the server

process. And all access to that table involves messages over the network.

If you want a "local" in-memory table, then you need to have a

TnxServerEngine in your application in addition to the

TnxRemoteServerEngine and you need to make sure your TnxDatabase that's

used to create the in-memory table is connected to that TnxServerEngine,

not the TnxRemoteServerEngine.