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Diffstat (limited to 'src/backend/access/spgist/README')
| -rw-r--r-- | src/backend/access/spgist/README | 18 |
1 files changed, 15 insertions, 3 deletions
diff --git a/src/backend/access/spgist/README b/src/backend/access/spgist/README index b55b0738320..7117e02c770 100644 --- a/src/backend/access/spgist/README +++ b/src/backend/access/spgist/README @@ -56,7 +56,7 @@ list and there is no free space on page, then SP-GiST creates a new inner tuple and distributes leaf tuples into a set of lists on, perhaps, several pages. -Inner tuple consists of: +An inner tuple consists of: optional prefix value - all successors must be consistent with it. Example: @@ -67,14 +67,26 @@ Inner tuple consists of: list of nodes, where node is a (label, pointer) pair. Example of a label: a single character for radix tree -Leaf tuple consists of: +A leaf tuple consists of: a leaf value Example: radix tree - the rest of string (postfix) quad and k-d tree - the point itself - ItemPointer to the heap + ItemPointer to the corresponding heap tuple + nextOffset number of next leaf tuple in a chain on a leaf page + + optional nulls bitmask + optional INCLUDE-column values + +For compatibility with pre-v14 indexes, a leaf tuple has a nulls bitmask +only if there are null values (among the leaf value and the INCLUDE values) +*and* there is at least one INCLUDE column. The null-ness of the leaf +value can be inferred from whether the tuple is on a "nulls page" (see below) +so it is not necessary to represent it explicitly. But we include it anyway +in a bitmask used with INCLUDE values, so that standard tuple deconstruction +code can be used. NULLS HANDLING |