How to trace service firebird - delphi

How to trace all events for service firebird server with delphi xe10?
This is my code:
my := TIBControlService.Create(Self);
my.ServerName := '127.0.0.1/3050';
my.Protocol := TProtocol.TCP;
my.LoginPrompt := false;
my.TraceFlags := [tfQPrepare, tfQExecute, tfQFetch, tfError, tfStmt, tfConnect, tfTransact, tfBlob, tfService, tfMisc];
my.Params.Add( 'user_name=SYSDBA' );
my.Params.Add( 'password=masterkey' );
// -----
mh := MonitorHook;
mh.TraceFlags := my.TraceFlags;
Self.IBSQLMonitor1.TraceFlags := my.TraceFlags;
mh.RegisterMonitor(Self.IBSQLMonitor1);
Self.IBSQLMonitor1.Enabled := true;
Memo1.Lines.Add( Format('GetMonitorCount: %d',[mh.GetMonitorCount]) );
my.Attach;
Memo1.Lines.Add( Format('Active: %s',[System.StrUtils.IfThen(my.Active,'yes','no')]) );
and
procedure TForm1.IBSQLMonitor1SQL(EventText: string; EventTime: TDateTime);
begin
Memo1.Lines.Add(EventText);
end;
Result:
GetMonitorCount: 1
Active: yes
[Application:]
:[Attach]
[Application:]
:[Query]
But this result is only from my application. When I connecting from another proces (ex.isql) my application not show this event.

When talking about Interbase/Firebird the term EVENT has a very specific meaning, the specific SQL command that sends text constants to clients, who subscribed to those.
See http://firebirdsql.org/file/documentation/reference_manuals/fblangref25-en/html/fblangref25-psql-coding.html#fblangref25-psql-postevent
However, the client should subscribe to the exactly the same text string, as posted by PSQL block. There were talks about enabling masks-based subscription, which would potentially made it possible to subscribe to all SQL events, like *.* matches all files in Windows, but for the best of my knowledge they never materialized.
That is what "event" means in Firebird, but it does not seem that is what you mean, instead it looks you want to monitor all the kinds of activity flowing between the SQL server and all the applications, starting with SQL commands and more.
If so, then there is no way to do it in general. You have to decide what exactly and why exactly do you want, and maybe there will be some partial solutions.
Firebird 2.5 introduced the so called Trace API, which allows you to subscribe to SOME of actions and be notified of them. This tends to introduce a significant load on the engine though, depending on how vague your subscription filters would be and how many requests the server receives - it might increase RAM and CPU usage up to total unusability.
The kinds of activity that can be subscribed for are limited. For example the process of reading BLOBs is not monitored. When I asked - I was struggling with the infamous "Invalid BLOB id" that was triggered by Delphi dbExpress library quirk - i was told that "no one ever needed this, and you have little reasons to need it too. You made a demo project, sent it to us - and we explained the behavior for you". THAT time having BLOBs access tracing would help me a lot, but to be objective, that was one and the only case I really needed it.
You might take a look at what you can get in general with Firebird Trace Manager - a CLI utility that is part of FB distribution, starting with 2.5.
You might take a look at Firebird Profiler, a free simplistic GUI tool from http://fbprofiler.sf.net
Commercial DB IDEs for Firebird, like IBExpert or UpScene TraceManager and probably others too, usually have Trace API support.
You may do your own implementation, using Trace API, starting with Program Files\Firebird\Firebird_2_5\doc\README.trace_services.txt and Program Files\Firebird\Firebird_2_5\include\ibase.h. It may also happen that 3rd party libraries like Unified Interbase or IBObjects have translated the API to Delphi. I think i saw something about trace in UIB but i am not sure. I would not expect though such a library to be part of Delphi distribution: from Delphi standpoint Firebird is direct competitor to their Interbase and IBX library would hardly have interest to diverge from their own Interbase by supporting Firebird-only functions.
Provided you only care about native applications like Delphi you might decide to make your own interposer fbclient.dll and install it on all the client computers instead of stock DLLs. Same for legacy-emulating GDS32.DLL, if used by your apps.
This DLL should totally provide all the API calls, both classic ones described in IB6 documentation at http://firebirdsql.org/en/reference-manuals/ with all the post-IB6 updates, and the new Firebird 3 "object oriented API".
It should log the calls in a way of your choosing, and then should proxy the call to the copy of original client DLL that you will hide for it with different file name. It should be installed instead of the standard client DLL on every computer you care to intercept and monitor.
It should not be very hard with the classic API, people were doing this, though did not publish. But the new ooAPI might be challenging.
It will only intercept applications, working through the fbclient.DLL interface. Java applications using Jaybird and C# applications using .Net Provider libraries would probably use underlying wire protocol skipping the fbclient.dll and thus your interposer too.

Related

experiences with firebird server over the internet with multiple clients?

Has somebody real experience with firebird databases over the internet?
I have a typical windows accounting/ERP software (done with delphi) that works with the firebird database server pretty well.. Now my users (300 aprox. now, but should increment) also want to work "in the cloud" (connecting from the office, from the laptop, from the house, etc.). It is a lot of work of recreating everything to a standard web application (let's say for example, HTML+CSS+JS+PHP+MYSQL), so I'm considering keeping the win client (I don't care about other OSes) but instead of the server living in the clients LANs moving it to a pair of dedicated servers that I will contract (one primary and one secondary againts failures for starting).
Searching I've come across this faq http://www.firebirdfaq.org/faq53/ that explains that the fb protocol it isn't ideal for working in the internet, but still all my users today have at least a 1MBbit/sec ADSL internet connection (I don't think that to be slow as the faq denotes).
Somebody have done this? what was the experience? how secure are fb servers for being open to the internet? how well they scale?
I know that building a "middleware" with SOAP for example will be more normal, but still the solution I'm evaluating here is much more fast and easy (still I have some work with the replication, backup, hearbreath services, but it's much less than redoing everything for the web).
Thanks! Edit: FB version: 2.5.
I had being trying to "push" the Firebird Core developers to improve the Firebird protocol to get better speed with high latency network (aka. Internet). Recently, Dmitry Yemanov published some articles in his blog about this subject (dyemanov.blogspot.com). It seems that there is margin for optimizations, and I would really like to see this coming in FB 2.5.3 and FB 3.0, although there is no warranty for this happening in those versions or anytime soon. You can vote in such improvement here: http://tracker.firebirdsql.org/browse/CORE-2530
Safety? You may try to set up a VPN. It also may help with speed, since most of the VPNs software out there (Zebedee, etc) can compress the data being transfered, helping to speed up data transfer in some cases.
Some of my customers do use Firebird traditional C/S over the internet. It is much slower compared to local network, and of course, how much slower depends basically on the link speed and latency. You can do some optimization at the client side too, using metadata cache, etc. but don't expect miracles with the currently protocol. I would say that for whole day working, using Terminal Services would be a better option for now.
The response about the scaling question
Firebird runs in production on large big iron servers : 512G of ram 100.000 concurrent users
We run Firebird to power larger systems (for 12 government agencies
and 3 banks). It has approximately 100000 end users multiplexed
through 2500 (max) pooled connections
https://plus.google.com/111558763769231855886/posts/Q1ACy1yyTgP
The protocol in Firebird 2.5 is improoved there is still room left for 3.0 but you can check
what is already done
http://asfernandes.blogspot.com/2009/07/network-latency-influence-on-firebird.html
And the future enhancements in 3.0
http://www.firebirdnews.org/?p=6953
To protect your connection i guess the best bet is ssl/ssh tunnel (it can be a opnvpn)
with high compression option
http://mapopa.blogspot.com/2010/11/securing-firebird-using-ssh-tunnel.html
FB protocol problem isn't about bandwidth, but latency. In my experience, some operations can be very slow over internet/VPN compared to LAN or local connection. I haven't examined issue further since I don't really run applications over internet connection.
However, I suggest three-tier model for application. Create own application server, which runs on database server/same network. Let the clients talk with application server and you get maximum performance.
There are some N-tier application/middleware frameworks for Delphi:
RemObjects SDK and DataAbstract
RealThinClient
kbmMW
Delphi's own DataSnap
MidWare
With those you can get data compression, encryption, binary messages (faster than SOAP) etc.
You can implement TCP/IP packets encryption/decryption directly in the firebird engine itself.
Personnaly, i have downloaded the Firebird 2.5 source code and injected secure tunnelization code directly in his low level communication layer (the INET socket layer). Now, encryption/decryption is done directly by the firebird engine for each TCP/IP packet both at the server side and the client side (fbclient.dll).
Then there is no need to re-structure the client application except adding one line of code that provide the secret key you choose to crypt communication to the fbclient.dll. The same secret key must be declared in the firebird.conf file of your server installation.
I have also implemented a proxy negociation solution in the fbclient.dll in order to allow to TCP/IP packets to pass throught any proxy server (like Microsoft ISA Server for example).
For us, this architecture is functional for more than one year in a real production system.
kbmMW CodeGear Edition is free but without source. It can be used for commercial apps.
Download it after registering at: https://portal.components4developers.com
In case you see certificate errors (you shouldnt but I know we have heard that some actually do), accept and ignore them. The site is valid despite the cert.error.
kbmMW CodeGear Edition contains a subset of kbmMW Professional Edition, but supports the following Delphi database API's:
Borland Database Engine
DBExpress
kbmMemTable
SQLite3
It supports binary, binary over HTML, XML and SOAP protocols in communication with clients.
It contains everything you need incl.
unified remote custom method invocation
unified remote dataset query, execute and data change resolving
unified database meta data handling and creation (tables, fields, indexes, generators/sequencers)
optional automatic proxying of requests to another server and proxying results back to original requester
full native XML DOM and SAX support
full dataset briefcase support as CSV, or binary data
advanced but simple to use wizard for creating new application server services
THere is one caveat though. Newest version of kbmMW CodeGear Edition always only supports newest Delphi version. You can still download older kbmMW CodeGear Editions matching older Delphi releases.
kbMMW Professional Edition and kbmMW Enterprise Edition do not have such limitations, and currently supports D7, D2006, D2007, D2010, DXE, DXE2 along with Embarcadero C++ counterparts.
best regards
Kim Madsen
www.components4developers.com

Sending and receiving data streams in Delphi

I want to create a software to connect to another and send some data (text based) to another program through the internet.
The software will send data every 300 milliseconds (using timer) and the receiver must receive the data on time.
The connection can be like the following
any data can be lost;
but the rest must arrive on time with minimum delay as possible (maximum 2 seconds);
the delayed data can be considers as lost, can be ignored.
I think it may be similar to a video conference software, but only using simple text as data.
Can anyone tell me how to make such a program, specifically
what kind of component can I use (any INDY examples);
what technologies do you recommend.
I have planned to do it with Delphi but other recommendation also welcome .
==========================update1 =================
Is it possible to send images through the stream
I suggest using UDP protocol and adding timestamp information to your data and track incoming data on the receiving end. You can use UDP server (TIdUDPServer) and client (TIdUDPClient) components from Indy or other packages. Client component is for sending data and server for receiving.
Personally I usually prefer Synapse -classes. They are lower level than Indy, so it's easier to know what's happening but on the otherhand you may need to implement something yourself what Indy may provide by default.
Update
Implementation is pretty straight forward:
Sending data:
Drop TIdUDPClient on the form. Set "Host" to name or IP address of receiving end (or "localhost" if you run your programs in same computer) and port to high number where server is listening, eg 54656.
Add following code to button or timer event:
IdUDPClient1.Send('Hello, world!');
Receiving data:
Drop TIdUDPServer component on the form. Set default port to same port as in sending application. Add OnUDPRead event handler, with code:
MessageDlg('Received: ' + StringOf(AData), mtInformation, [mbOk], 0);
And new message dialog pops up everytime new message is received.
Update 2
UDP is not good for images, if you want to be sure they will stay uncorrupted, unless the image is very small and fits inside one packet.
I'd recommend using anything but Indy. It is both buggy (especially versions bundled with Delphi) and slower than other component sets. It is easy to understand and start using it, but once you delve deeper under the hood, you start noticing small problems. Indy is constantly under development and you can find latest build here. Problem is that you can't easily replace the bundled version with newer in Delphi versions from 2009 onward because of some hard-coded dependencies.
Delphi has few other network communication methods integrated, but I recommend exploring 3rd party components. First, if you want open source, you should take a look at Overbyte ICS. It is a bit difficult to master, but it has good performance and feature set.
As a very good commercial solution, take a look at IP^Works. I have only scratched it, but from what I saw, I can wholeheartedly recommend it.

Wiki: Current state of the art of Delphi 3rd party TCP/IP components libraries

I've not been doing bare metal TCP/IP for about 18 months, so I wonder what the current state of the art is.
I'm looking for both positive and negative aspects, with development of both server and client software.
I will be doing a project that needs a rock-solid TCP/IP layer, so for me that is an important aspect :)
For this to become a community wiki, I'm looking for broader answers than just 'rock solid'. So for instance information about the feature-width is also appreciated.
I'll be updating the question with relevant aspects found in the answers in order to get a wiki entry that has a balanced overview of those libraries.
For example, see my answer below with my past experience with Indy
I'm ambivalent on the exception handling and anti-freeze in Indy, though I got used to it, it still felt somewhat unnatural.
Right now I develop in both Delphi 2007 (non Unicode) and XE (Unicode), so the libraries I'm considering should support at least those two Delphi versions.
Edit: Summary of my past experience with Indy, and the comments (thanks Eugene, Marjan)
(please update with the current Indy state of the art):
Pro:
ships with Delphi
mature
development community
open source so lots of eyes scrutinizing those sources
a truckload of valuable comment documentation in the source code
OpenSSL support
supports a broad set of Delphi versions (including 2007 and XE)
wide choice of protocols
Con:
the version shipping with Delphi was not always the most stable one; download from the sources was usually required to get a stable build
(in the mean time) lots of duplication of code that now is in Delphi (but Indy requires for compatibility with older Delphi versions)
not all TCP/IP components were up-to-date (for instance, back then the POP3 client component did not support some basic POP3 commands)
version interoperability was a pain: upgrading from one Indy version to another could be very time consuming
I'm ambivalent on the exception handling and anti-freeze in Indy, though I got used to it, it still felt somewhat unnatural.
breaking changes are made between build updates; ifdefs required to accommodate those
Unclear release status if any at all, no RCs for a long while, getting trunk can make your local copy unstable
ICS - The Internet Component Suite
ICS - see www.overbyte.be. Open source by François Piette. To me this has always been the number 1 alternative to Indy. It's most interesting selling point: it makes using asynchronous stuff easy, and being async seems to be closer to "bare metal" sockets programming.
I've used it to build a fairly complex VNC proxy where the proxy itself (server) is built with ICS and the clients are a mixture of Indy and ICS. In periods of high demand the proxy handles about 100 simultaneous connections and about 10 simultaneous VNC screen sessions. It eats up an average of 5 mbit/s, handles connections over two distinct Internet connections. I don't think the 100 + 10 is the limit, because the server handles that without any problems and CPU usage is too low to mention.
Pros:
Works asynchronously
Somewhat easier on beginners because it doesn't need threads
Supports a good number of protocols
Cons:
Relies on Windows messaging. I'm simply not comfortable with that.
The async behavior makes implementing most protocols slightly difficult (because most protocols are in the form of send command / receive response). This shouldn't matter for most people since ICS offers ready-made implementation for the most-used protocols.
All that being said, I haven't used ICS in a very long time, I'm not up-to-date with all the bells and whistles. This is CW, so please edit and expand!
I have used Indy since 2003 for my own TCP communications framework. It is rock-solid, I have a version used with Delphi 2007 and another with Delphi 2010, if you handle the threadng correctly there is no need to use the anti-freeze stuff, and I have consistent exception handling on the client and the server by implementing my own wrapper around this.
You can dowload it here (http://www.csinnovations.com/framework_delphi.htm) - look for the Tcp units, mainly AppTcpServerUnt and AppTcpClientUnt.
I would strongly recommend Clever Internet Suite, it's by far the best designed and written set of communication components. It's not free and so not that well known, but it's well worth investigating.
Pro:
well designed and written
contains many components and implements various protocols.
supports a broad set of Delphi versions (including 2007 and XE)
SSL support
mature product as the release history indicates
Con:
not open source
You could consider using a higher protocol level like HTTP, because:
It's more firewall and VPN friendly;
It's well documented and known as a good protocol;
It already has secured HTTPS version;
It has a very low overhead over row TCP/IP;
It's ready to use in an AJAX environment (if you need it in the future);
Microsoft already did the low-level tuning for you in modern version of Windows.
In this case, you could take a look at two Open Source classes working from Delphi 6 up to XE:
THttpApiServer which implements a HTTP server using fast http.sys kernel-mode server:
The HTTP Server API enables applications to communicate over HTTP without
using Microsoft Internet Information Server (IIS). Applications can register
to receive HTTP requests for particular URLs, receive HTTP requests, and send
HTTP responses. The HTTP Server API includes SSL support so that applications
can exchange data over secure HTTP connections without IIS. It is also
designed to work with I/O completion ports.
The HTTP Server API is supported on Windows Server 2003 operating systems
and on Windows XP with Service Pack 2 (SP2). Be aware that Microsoft IIS 5
running on Windows XP with SP2 is not able to share port 80 with other HTTP
applications running simultaneously.
TWinHTTP which handles client-side HTTP/1.1 request using the WinHTTP API:
Microsoft Windows HTTP Services (WinHTTP) is targeted at middle-tier and
back-end server applications that require access to an HTTP client stack;
Is much faster than older WinINet API.
Resulting speed is very good (especially the server), and you will rely on Microsoft implementation. The first is the core of IIS, and the second is used in the latest versions of Internet Explorer.
The answer really depends on many factors and your requirements, such as
what layers are needed (TCP, SSL/TLS, application-level protocols)
whether you need a client or a server as well (server is much more complicated task)
whether you count paid options.
In general, not much (positive) happened in 18 months or even in 3 years as most developers look at .NET as primary development platform.
Clever Internet Suite mentioned in other answer and DevArt's SecureBridge gained some new functionality.
Our SecureBlackbox offers support for the most advanced features (besides native SSL/TLS): IPv6, HTTPS Proxy with basic, digest and NTLM authentication (starting with SecureBlackbox 9), International Domain Names (starting with SecureBlackbox 9), DNSSEC, bandwidth control and more.
Application-level protocols supported by SecureBlackbox are HTTP (client and server), WebDAV (client and server), FTP (client and server), SSH and SFTP (client and server), SMTP and POP3 clients, DNS client, AS2 and AS3. All of the protocols (besides SSH and SFTP, of course) have complete support for SSL/TLS.
The list of supported protocols can be found on Packages page. Supported protocol features are listed on Technical Specification page for each package.
Worked with NetMaster components way (way!) back in the old Delphi versions (2! 3! 4!)
Did some work with Indy, but had the unnatural feeling also (actually I'd describe it more as bulky)
Stumbled upon Synapse when I was searching for just a light wrapper around the Windows network API,
And then rediscovered plain old TTcpClient/TTcpServer. They are Delphi's own wrapper around winsock! I use them blocking, with a dedicated TThread inheritant for each TTcpClient, and let TTcpServer do the threads and do all the work in DoAccept, see here for an example.
This, fow now, gave me the rock-solid feel we're looking for. If you want to support heavy load, I would try and build a thread manager that handles several sockets/connections per thread, or have two sets of threads: a few that listen a larger number of 'dormant' connections, and the others that handle lesser 'active' connections, switching connections between the threads depending on wether a request or response is being handled. (e.g. HTTP's Connection: keep-alive)

Delphi Server Socket component

We have a C/S application all written in Delphi (Client and Server-or middleware if you want)
For the client part we use Indy.
For the server we use DXSock.
Since DXSock is dead for a while we are investigating alternatives for the sever part.
I want to hear some comments about the best Server Socket alternative component for Delphi.
The current system usually have tens of permanent connections working each one on its own thread but could be hundreads in the future (this should be improved to a thread pool if possible)
If you want to have the best possible performance, you'd have to use sockets in non blocking mode, or using completion ports. IPWorks is implemented like that, as well as iocp. As far as I can tell, Indy or Synapse don't implement them (at least officially).
We used completion ports and a thread pool in our open source SynCrtSock unit, used in our Synopse SQLite3 framework.
Here are some benchmarks of this solution, working from Delphi 6 up to Delphi XE. I don't tell this is the "best component", but it's a working and speedy one (every request is about 4 KB of JSON data):
Http client keep alive (i.e. one HTTP/1.1 client connection kept alive during requests):
first in 7.87ms, done in 153.37ms i.e. 6520/s, average 153us
Http client multi connect (i.e. one new HTTP/1.0 client connection created for each request - this one uses completion ports and a thread pool):
first in 151us, done in 305.98ms i.e. 3268/s, average 305us
For speed comparison, here are other communication protocols available in our framework:
Named pipe access:
first in 78.67ms, done in 187.15ms i.e. 5343/s, average 187us
Local window messages:
first in 148us, done in 112.90ms i.e. 8857/s, average 112us
Direct in process access:
first in 44us, done in 41.69ms i.e. 23981/s, average 41us
We use HTTP/1.1 protocol over TCP/IP, because there is very little overhead over plain TCP/IP, and this is a well handled protocol for firewalls and such, and allows our framework to be used by an AJAX application, whereas its main purpose is to serve Delphi clients.
IMHO there is no "best Server Socket alternative component for Delphi", it depends what is the purpose of your server application. The main bottleneck will be in the Windows kernel itself. Perhaps direct access to the HTTP Kernel-Mode Driver (Http.sys) of Windows could help.
Consider using a dedicated optimized Server instead of a Delphi server, like lighttpd or Cherokee using FastCGI to handle the requests via a Free Pascal (or CrossKylix) application, under Linux. I guess this will be the best performance possible.
I use Indy components for commercial server-side work and the component set is pretty solid (9 or 10). My servers have millions of connections per day with no issues.
I used DXSock many moons ago. He was always optimizing, but never seemed to finish it. He does seem to have another version out.
If you want commercial support, then I'd recommend IPWorks from nSoftware.
Actually DXSock is not dead, v6.1 was just released. The web hosting company we used to use in Tennessee lost the domain - so only customers who have kept their subscription renewed annually have received DXSock 5.0, 6.0 and 6.1.
Indy CANNOT support more than 2,000 concurrent connections on 32bit Windows - as Chad and crew use TThread, which implements the defacto 1MB per thread/socket connection - 2000x1MB = >2.5GB of RAM which 32bit OSes do not support. DXSock implements a 0b per connection model (unless you define otherwise) and can handle over 50,000 concurrent on Windows, Linux, Mac, Pi, etc.
Ozz Nixon - ozznixon#bpdx.com if you want more details on 6.1
Author of DXSock
Co-Author of Winshoes which became INDY.

Which Delphi technology to use?

I have a Client/Server application written Delphi. Essentially all the application is doing is transferring xml data streams between a server application and connected clients. I am currently using the Indy TIdTCPServer component. But the server side application keeps crashing on some of my installments. And it has been extremely difficult to debug. So I am wondering if there is some "architecture" I should be utilizing which does all the tcp/ip connection management and database connection pooling, allowing me to concentrate on the business logic.
Here are more details:
clients must maintain a "persistent" connection. There are times when the server must notify and send data to all connected clients.
clients are connecting from laptop computers using wireless aircards. So network "drops" are pretty common.
Backend database is SqlServer.
There can be upward of 100 computers simultaneously connected at a time.
When the server gets a new connection (TCPServer.OnConnect) I instantiate my own object containing it own SqlServer database connection. When tcp connections are dropped I in turn free these objects (and associated database connection).
Client application have a TTimer built into them. They routinely send heartbeats to the server. And if they "drop"/"lose" their connection they automatically establish a new connection once the network is back.
Anyone have any suggestions on the best approach/architecture here?
I presume the Indy component would work, but at the same time feel I am "reinventing the wheel" with respect to managing the connections.
Three component sets I am aware of that will take care of the nitty gritty technical aspects of client server applications for you:
kbmMW: http://components4developers.com/
Asta: http://www.astatech.com/index.asp
RemObjects: http://www.remobjects.com/
You may have to rework your applications to take advantage of the way these component sets work, but assuming you have properly separated layers that shouldn't be too much of a hassle and will buy you the advantage of well tested and widely used code for your client server work.
If you want some light TCP/IP components, take a look at our SynCrtSock unit.
You'll find low-level classes to create IP Client and Servers.
We implemented both TCP/IP and UDP/IP in one of our applications.
There is also a THttpServer class, which implement a HTTP/1.1 server. Therefore it follows the HTTP/1.1 connection management. There is also an optional compression, and using HTTP/1.1 on a port other than 80 is not a bad idea. And what is good with HTTP/1.1 is that it can pass through firewalls, and can be easily be VPNed or hosted on another HTTP server (like IIS or Apache) with a proxy. There is even a FastCGI class, if you need such a server under a linux-based solution.
Of course, a THttpClientSocket class does the same on the client class.
We use these classes to add HTTP/1.1 connection to our Open Source SQLite3 RESTful framework - http://synopse.info/forum/viewforum.php?id=2
See http://synopse.info/fossil/artifact?name=722e896e3d7aad1fe217b0e2e7903483e66d66d1 for the SynCrtSock unit. Open source, work from Delphi 7 to Delphi 2010.
Misha Charrett's CSI Application Framework covers pretty much exactly what you're asking for.
It's an open source Delphi framework that at its heart is a distributed message passing and threading framework that allows XML message passing from both client to server and server to client.
It can handle disconnections/reconnections, high client numbers and there's an optional virtual database library that will handle SQL server (or you could just use same SQL Server access you're using now).
It's not particularly well known yet but I can tell you that it's been actively developed over the last few years and that the author Misha is very keen to assist anyone who's interested in using it in their application.
Well, it would probably require a complete rewrite of much of your C/S code, but instead of using the Indy components, you could try to use a COM+ solution instead. Basically, you would create a COM+ component that will be installed on the server and your client applications will connect to this client and call the functions of this component directly. It will have transaction management which will be handled by Windows itself and the same is true about handling transactions. It's also technically possible to create events, which would allow the server to do callbacks to the client, although that would make things a bit more complicated.
I don't think this solution would work out for you, though, unless you have a lot of experience with COM development in Windows and/or you're brave enough to try something different.
In the past, I had a similar problem where hundreds of clients had to connect to a single server, doing all kinds of database transactions. It has a steep learning curve but me and my team managed to get things working and once we understood the technique, it resulted in a very stable and reliable solution which did manage to have up to 500 users simultaneously doing updates and other actions in a one-time extreme stress-test. But again, the learning curse is steep, so it might not be the solution you're looking for.
(Still, COM+ will use a lot of functionality that's build-in into Windows, like transaction management, database pooling and whatever more.)
If you use Indy each connection will equal a thread.
Anyway, I suggest for connecting to MSSQL to use SDAC from Devart http://www.devart.com/sdac/ and for the connection layer to use HPScktSrvr based on I/O Completion Port from http://www.torry.net/authorsmore.php?id=7131 (I don't know though what changes it will need for TThread changes in newer VCL).
You build your client class arround THPServerClient, you set your new class as the server ClientClass and the framework will create automatically new clients for you.
You may also want to have a look at the ICS/Midware combo: http://www.overbyte.be/

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