The indexes used in Apache Solr are inverted indexes. In case of the inverted indexing technique, all your text will be parsed and words will be extracted out of it. These words are then stored as index items, with the location of their appearance. For example, consider the following statements:
"Mike enjoys playing on a beach"
"Playing on the ground is a good exercise"
"Mike loves to exercise daily"
The index with location information for all these sentences will look like following (Numbers in brackets denote (sentence number, word number)):
Mike (1,1), (3,1) enjoys (1,2) playing (1,3), (2,1) on (1,4), (2,2) a (1,5), (2,5) beach (1,6) ground (2,3) is (2,4) good (2,6) loves (3,2) to (3,3) exercise (2,7), (3,4) daily (3,5)
When you perform a delete on your inverted index, it does not delete the document; it only marks the document as deleted. It will get cleaned only when the segment that the index is a part of is merged. When you...