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Added some comments about Antelope and Coffee.

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nvt 2012-10-30 01:56:23 +01:00 • committed by Nicolas Tsiftes
parent 31da83d0a3
commit 757a54f63c
6 changed files with 89 additions and 28 deletions
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17
apps/antelope/index-maxheap.c
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@ -29,9 +29,9 @@
/**
* \file
* An binary maximum heap for data indexing over flash memory.
* MaxHeap - A binary maximum heap index for flash memory.
*
* The idea behind this method is to write entries sequentially
* The idea behind the MaxHeap index is to write entries sequentially
* into small buckets, which are indexed in a binary maximum heap.
* Although sequential writes make the entries unsorted within a
* bucket, the time to load and scan a single bucket is small. The
@ -114,6 +114,7 @@ struct bucket_cache {
bucket_t bucket;
};
/* Keep a cache of buckets read from storage. */
static struct bucket_cache bucket_cache[DB_HEAP_CACHE_LIMIT];
MEMB(heaps, heap_t, DB_HEAP_INDEX_LIMIT);
@ -504,7 +505,7 @@ create(index_t *index)
bucket_filename[0] = '\0';
/* Generate the heap file, which is the main index file that is
inserted into the metadata of the relation. */
referenced from the metadata of the relation. */
filename = storage_generate_file("heap",
(unsigned long)NODE_LIMIT * sizeof(heap_node_t));
if(filename == NULL) {
@ -693,7 +694,8 @@ get_next(index_iterator_t *iterator)
cache.found_items = cache.start = 0;
cache.index_iterator = iterator;
/* Find a path of heap nodes which can contain the key. */
/* Find the downward path through the heap consisting of all nodes
that could possibly contain the key. */
for(i = tmp_heap_iterator = 0; i < NODE_DEPTH; i++) {
cache.visited_buckets[i] = heap_find(heap, key, &tmp_heap_iterator);
if(cache.visited_buckets[i] < 0) {
@ -706,7 +708,8 @@ get_next(index_iterator_t *iterator)
/*
* Search for the key in each heap node, starting from the bottom
* of the heap. There is a much higher chance that the key will be
* of the heap. Because the bottom nodes contain are very narrow
* range of keys, there is a much higher chance that the key will be
* there rather than at the top.
*/
for(; cache.heap_iterator >= 0; cache.heap_iterator--) {
@ -719,8 +722,8 @@ get_next(index_iterator_t *iterator)
return INVALID_TUPLE;
}
/* Compare the key against the bucket_ids in the bucket sequentially because
they are placed in arbitrary order. */
/* Because keys are stored in an unsorted order in the bucket, we
* need to search the bucket sequentially. */
next_free_slot = heap->next_free_slot[bucket_id];
for(i = cache.start; i < next_free_slot; i++) {
if(bcache->bucket.pairs[i].key == key) {