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Diffstat (limited to 'src')
| -rw-r--r-- | src/backend/access/nbtree/README | 13 |
1 files changed, 12 insertions, 1 deletions
diff --git a/src/backend/access/nbtree/README b/src/backend/access/nbtree/README index e771798dc58..cff7ff0d655 100644 --- a/src/backend/access/nbtree/README +++ b/src/backend/access/nbtree/README @@ -1,4 +1,4 @@ -$Header: /cvsroot/pgsql/src/backend/access/nbtree/README,v 1.3 2000/07/21 22:14:09 tgl Exp $ +$Header: /cvsroot/pgsql/src/backend/access/nbtree/README,v 1.4 2000/07/25 05:26:40 tgl Exp $ This directory contains a correct implementation of Lehman and Yao's high-concurrency B-tree management algorithm (P. Lehman and S. Yao, @@ -119,6 +119,17 @@ In addition, the following things are handy to know: exists only to support VACUUM and allow it to delete items while it's scanning the index. ++ "ScanKey" data structures are used in two fundamentally different ways + in this code. Searches for the initial position for a scan, as well as + insertions, use scankeys in which the comparison function is a 3-way + comparator (<0, =0, >0 result). These scankeys are built within the + btree code (eg, by _bt_mkscankey()) and used by _bt_compare(). Once we + are positioned, sequential examination of tuples in a scan is done by + _bt_checkkeys() using scankeys in which the comparison functions return + booleans --- for example, int4lt might be used. These scankeys are the + ones originally passed in from outside the btree code. Same + representation, but different comparison functions! + Notes about data representation: + The right-sibling link required by L&Y is kept in the page "opaque |