FAQ: ArcIMS and Direct Connect? Part Two

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** Internal Publish Only! This article may contain information that is not intended for external circulation. **

A collection of FAQs for ArcIMS 3.1 or 4.0, "Direct Connect", and ArcSDE. This information will not be made public, but individual answers can be distributed on an as-needed basis. Note that although Direct Connect will work with many ESRI products, these FAQs pertain almost exclusively to ArcIMS. Alan Jackson is the original author of all the items below.

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Q15: How does direct connect work? What is the technical explanation?
A15: The program that ran separately as ArcSDE is delivered as about three DLLs at ArcSDE 8.1 an 8.2. These DLLs now execute each time ArcIMS requests ArcSDE layers. We call this running ArcSDE "in process".

Q16: By running ArcSDE in process are we saying that direct connect is faster than using ArcSDE?
A16: No. Direct connect is 20-30% slower than using ArcSDE. ArcSDE will process SQL and prepare data before it gets to the client without using the database server. This means that often the HTML or Java client will only need to consult the ArcSDE middleware for processing. Without this middle tier, direct connect must access the database server for each query and each process that requires SQL. We say that this means there is a "full round trip" between ArcIMS and the database server when running direct connect.

Q17: Does direct connect take up more resources than ArcSDE?
A17: Yes. Aside from the increased network traffic just described, running direct connect will add 8-10 MB to the memory size of the spatial server. Additional memory is required because ArcSDE runs in process. Most of the 8-10MB of memory is used by the Oracle libraries.

Q18: Does this mean that ArcSDE is slower than Oracle Spatial?
A18: No. Absolutely not. We know from benchmarks at ESRI and elsewhere that ArcSDE is much faster when used as middleware and when direct connect is used.

Q19: How do I register Oracle 8i/9i Spatial data with the Geodatabase tables so that a direct connect can be achieved via ArcIMS?
A19: At ArcSDE 8.1 and 8.2, tables with Oracle Spatial geometry are "autoregistered" to the geodatabase and ArcSDE. When a user connects using either ArcSDE application server or direct connect, ArcSDE will interrogate all the tables in the database to determine which ones have Oracle Spatial geometries in them. This is why the select any table privilege is required for the SDE user. All tables must be interrogated because there is an inconsistency in the Oracle Windows and Oracle Unix products. The only way to consistently get this information is to have the select any table privilege. The autoregistration process works quite well when using direct connect from ArcIMS 3.1 and 4.0 because the underlying autoregistration process is the same for ArcSDE direct connect and application server.

Q20: Where can I get more information about direct connect?
A20: The following ESRI publications describe setup, installation of direct connect with ESRI's products.
1. ArcIMS 3.1 Install Guide, Appendix C "Installing and Setting up the ArcSDE direct connect drivers" or at ArcIMS 4.0, "Direct Connect and ArcIMS"
2. "ArcSDE Configuration and Tuning Guide for Oracle".
3. "ArcSDE Installation Guide for Oracle"
4. "ArcSDE Configuration and Tuning Guide for SQL Server".
5. "Understanding ArcSDE"

Q21: Which products support direct connect?
A21: All ESRI products that support a geodatabase also support direct connect. This includes version 8.1 and 8.2 of ArcCatalog, ArcMap, and ArcView, MapObjects 2.1 and ArcIMS 3.1 or 4.0. ArcInfo 8.1 workstation/unix also supports direct connect but the connection is slow.

Q22: What kinds of data are supported by direct connect?
A22: Direct connect supports both vector and raster layers.

Q23: What is the impact on the number of ArcSDE connections when direct connect is used?
A23: None. ArcSDE Connects are not checked out when direct connect is used.

Q24: How are error messages by direct connect?
A24: Direct connect uses the sde.errlog file. The logfile is written to the etc directory under the SDEHOME or ARCHOME location. There is no difference between error handling in direct connect and error handling with the ArcSDE application server.

Q25: If I use direct connect with ArcIMS will any ArcSDE connects be checked out and will the connection show up as an ArcSDE connection?
A25: No. ArcSDE connects are not checked out when direct connect is used. If you type "sdemon -o info -I users", users accessing ArcSDE layers through direct connect are not listed.

Article ID:000004935

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ArcIMS and Direct Connect? Part Two

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