Also, if you are thinking that accessing the "buffer" directly will
be faster than "parsing" the packed structure, I'm not so sure.
You can review the source for the various buffers, and since the is
no "struct" support in Java, you end up combining bytes to make
longs, etc. Also, a lot of the accesses are though Unsafe, which is
slower than the indirection on a Java object to access a field.
My review of these classes makes me think that parsing the "skip to"
index once into java objects for later use is going to be a lot
faster overall than accessing the entire mapped file directly on
every invocation.
On Dec 23, 2008, at 9:20 PM, Marvin Humphrey wrote:
On Tue, Dec 23, 2008 at 08:36:24PM -0600, robert engels wrote:
Is there something that I am missing?
Yes.
I see lots of references to using "memory mapped" files to
"dramatically"
improve performance.
There have been substantial discussions about this design in JIRA,
notably LUCENE-1458.
The "dramatic" improvement is WRT to opening/reopening an IndexReader.
Presently in both KS and Lucene, certain data structures have to be
read at
IndexReader startup and unpacked into process memory -- in
particular, the
term dictionary index and sort caches. If those data structures
can be
represented by a memory mapped file rather than built up from
scratch, we save
big.
Marvin Humphrey
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