Sphinx or Yandex.Server?

4000 or 4,000,000 for articles?
You can put both.
Yandex server capricious in settings and heavier with the documentation. A year ago there was a problem with the encoding when indexing via mysql, as it managed to get around.
But there are also bonuses, in particular the finished results with light. For a small number of documents Yandex perhaps convenient. The main difference — Yandex when searching saves you from extra access to the database of documents.
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The Sphinx is much simpler rises, documentation, no problem (live forum) and more flexible in settings.
For really big databases Sphinx will give hundred points forward to a third because of the ability to store a large part of the base on the screw ( the direct problem ).
the lack of the Sphinx in the need to climb into the sql database handles during the international search (in the latest beta have the opportunity to store the sample in the base of the Sphinx, but it and betka to be uncomfortable. on small databases usability, in large — inhibits).
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Living examples: on the basis of the orders of magnitude of hundreds of millions of records have been selected the Sphinx. Yandex stupid couldn't survive on one machine (have not found it a mode that allows you to minimize the amount of memory).

Sphinx, Yandex.The server is very picky about the OS and settings (kuuucha spent time on his zapilivanija)

I do not remember, whether there is at Yandex.the server can index the database itself, in contrast to the Sphinx. Afaik it only http crolet and files on the screw can preindexing. behind this warning is easier to set the Sphinx at the base or Yandex.the server on the website.
in General, it depends on what you actually want to index the page or column in the database table, and then screw that will fit.
something like this. a couple of times Yandex.the server is set, any difficulties I do not remember. the Sphinx did not put, I can not compare.

In J. monoadesivi With database MySQL and any other ODBC.
Raised and the Sphinx and Ya, of course Ya have relevance With the above, but he takes too long to index the site from 450,000 pages approximate time — 2 hours, and during indexing he needs 2 gig on the screw that was free(number of pages). And when he starts to merge the indexes, the server is hung up, the host complained constantly that my server eats more operatives than you(2giga). In short, You decide, but with 4M articles I would if put With Ya, on a separate server.