I would like to know the Size Limit of Attachments when using MTOM streaming in webMethods 9.5 web services?

Check the below settings on IS

watt.server.SOAP.MTOMThreshold
watt.server.SOAP.MTOMStreaming.threshold

Also the size of the MTOM attachment that IS can handle completely depends on the memory configured for IS, definitely it can’t be as big as the heap size.

Its good to have some benchmark testing for a JVM Max Heap Size configured to IS.

Those setting is when MTOM will be used, not upper limit.

watt.server.SOAP.MTOMStreaming.threshold
Specifies the number of bytes an MTOM a?achment in an inbound SOAP
message must be before Integration Server uses MTOM streaming for the MTOM
a?achment. This parameter takes effect only when MTOM streaming is enabled (i.e.,
wa?.server.SOAP.MTOMStreaming.enable is set to true).
Set the property to a positive integer to indicate the number of bytes for the MTOM
streaming threshold. Integration Server uses MTOM streaming when an MTOM
a?achment is larger than the number of bytes you specify. The default is 4000 bytes.
watt.server.SOAP.MTOMThreshold
Specifies the field size, in kilobytes, that determines whether Integration Server handles
base64binary encoded data in an outbound SOAP request as a MIME a?achment or
whether it sends it inline in the SOAP message. If the web service descriptor for the
SOAP message enables a?achments for the SOAP request, Integration Server passes
as MIME a?achments any base64 fields in a SOAP message that are larger than the
threshold. The default is 0.

If you are only streaming (not converting it to in memory objects), there shouldn’t be limit.
But you normally have to convert it to in memory objects, so better test it out.

Yes I echo with those settings and also make sure your IS memory also handles that MTOM threshold while basic bench mark testing is good to have before releasing to prod updates.

HTH,
RMG