bq. I have been informed that the performance of such a search is absolutely terrible.
Yep. Horrible. These two structures answer completely different questions indexed - "for this word, what docs contain it in field X?" DocValues - "for this document, what is the value of field X?" On my, my usual examples are going out of date. "phone book" and "dictionary". There used to be, in the old days, these book-like things that were printed on actual paper and you could use them to find people's phone number and address, or what the meaning of a word was. Siiiiggghhhh. Well, get a paper phone book from somewhere off the shelf and consider each entry a "document", and the phone number and address the "text" DocValues answers "for person X, what is the phone number" easily, the whole thing is alphabetically arranged. But to answer the question "Who lives on Maple street" you have to read _everything_ in the entire phone book. Think "table scan". To answer the question "Who lives on Maple street", you want to index all the text. The whole point of docValues was that the structure that was used to answer the first question was built in the heap at runtime, consuming memory and CPU cycles. DocValues serialized that structure to disk at index time where it is 1> easily read as memory pages 2> almost entirely kept in MMapDirectory space, see: http://blog.thetaphi.de/2012/07/use-lucenes-mmapdirectory-on-64bit.html Best, Erick On Sun, Aug 12, 2018 at 8:56 AM, Shawn Heisey <apa...@elyograg.org> wrote: > On 8/12/2018 4:39 AM, Zahra Aminolroaya wrote: >> >> Could we say that docvalue technique is better for sorting and faceting >> and >> inverted index one is better for searching? > > > Yes. That is how things work. > > If docValues do not exist, then an equivalent data structure must be built > in heap memory *from* the inverted index in order for faceting or sorting to > take place. When docValues are present, Solr can just read the data > directly instead of generating it. If there is plenty of spare memory for > the OS to cache data, this is faster. It also uses less Java heap memory. > >> Will I lose anything if I only use docvalue? >> >> Does docvalue technique have better performance? > > > From what I understand, it actually is possible to search when docValues are > present but the inverted index isn't, assuming that what you're searching > for is the full value of the field, not an individual word. I have been > informed that the performance of such a search is absolutely terrible. > > Thanks, > Shawn >
