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authorArseny Kapoulkine <arseny.kapoulkine@gmail.com>2014-10-01 07:02:52 +0000
committerArseny Kapoulkine <arseny.kapoulkine@gmail.com>2014-10-01 07:02:52 +0000
commitfebe4f0209f86225ebeedfb0874feb3cb96e7c89 (patch)
tree88e590e12b404bdfcc09f8e822889647c8d005a5 /docs/images/caution.png
parent89d19df43df8e7962bcf896a528d3214a3c28bbc (diff)
Implement copyless copy
Now copying nodes or attributes does not copy names/values if the source strings are in a document buffer. As a result, several nodes can now share the same string in document buffer - to support this we 'taint' both source and destination with a special 'shared' bit. Tainting disables offset_debug() and fast-path document order comparison; it also prevents strcpy_insitu from reusing the document buffer memory for the copied node. The downsides include slower XPath queries in some (rare) cases and slightly higher memory consumption in some (rare) cases. XPath queries can execute slower if a lot of old nodes were copied to new nodes *and* a query only touches old nodes (so it used to benefit a lot from fast comparison path) *and* a query produces unsorted node sets that need to be sorted later (both are relatively rare). Higher memory consumption is possible if a lot of nodes were copied and all nodes (both new and old) have their contents modified 'in place' -- previously we could modify the old node in place and the new node required one allocation on copy, and now both nodes have to have their data allocated during modification. This should also be rare. On the bright side, in a lot of cases copying of string data can be avoided - this makes the copy much faster and the document now occupies less memory. For example, some uses of append_buffer are now actually slower compared to building up a document by copying a template from the same document and modifying the copy slightly. In one of the internal benchmarks copying is now 4x faster (the difference can be more dramatic with more string contents and less markup). git-svn-id: https://pugixml.googlecode.com/svn/trunk@1032 99668b35-9821-0410-8761-19e4c4f06640
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