/ Changes On Branch in-scan-vs-index

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Changes In Branch in-scan-vs-index Excluding Merge-Ins

This is equivalent to a diff from 43f7ddad80 to dc4172e6b8

Improved query optimization for multi-column indexes where the second or later columns are constrained by an IN operator and the earlier index columns limit the search to a small number of rows. Use the new OP_SeekScan opcode which does scanning of the relevant range of the index but gives up and falls back to doing a seek if the number of rows scanned grows to large, in order to guard against pathological cases where the estimated number of rows to be scanned is far too small. (check-in: 4a43430fd2 user: drh tags: trunk)
For the OP_SeekScan opcode, adjust the number of steps run before giving up based on the estimated number of comparisons needed to perform a seek. (Closed-Leaf check-in: dc4172e6b8 user: drh tags: in-scan-vs-index)
Better understanding of savepoint code (check-in: ce6d8d6215 user: shearer tags: trunk)
Add an sqlite3FaultSim() call to btreeNext() to make it easier to simulate I/O errors in calls to sqlite3BtreeNext(), and in OP_SeekScan. (check-in: 29cca775d3 user: drh tags: in-scan-vs-index)
Revisiting the IN-scan optimization to try to fix it for the corner case where the statistics deceive the query planner into using a scan when an indexed lookup would be better. This check-in changes the code generation to do the IN-scan using a new OP_SeekScan opcode. That new opcode is designed to abandon the scan and fall back to a seek if it doesn't find a match quickly enough. For this work-in-progress check-in, OP_SeekScan is still a no-op and OP_SeekGE still ends up doing all the work. (check-in: d720b6981e user: drh tags: in-scan-vs-index)
Small performance improvement and size reduction by reducing the size of the WhereTerm object. (check-in: 43f7ddad80 user: drh tags: trunk)
Avoid the possibility of integer overflow on the --pagecache option to the CLI. See [forum:10a2892377|forum post 10a2892377] (check-in: d3d13df31a user: drh tags: trunk)

Changes to src/btree.c.

Changes to src/vdbe.c.

Changes to src/where.c.

Changes to src/whereInt.h.

Changes to src/wherecode.c.