Improved comments on the new OP_SeekScan opcode.
FossilOrigin-Name: 6110fdd5bb7b4ae5c065404c802ae726362ef084966b73cffe58c4bfb98689d2
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C Improved\sperformance\sby\smanually\sin-lining\sthe\ssqlite3VdbeIdxKeyCompare()\nroutine\sfor\sthe\sOP_IdxGT\sopcode\sand\sits\skin.
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D 2020-09-29T16:05:09.270
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C Improved\scomments\son\sthe\snew\sOP_SeekScan\sopcode.
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D 2020-09-29T17:29:11.276
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F .fossil-settings/empty-dirs dbb81e8fc0401ac46a1491ab34a7f2c7c0452f2f06b54ebb845d024ca8283ef1
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F LICENSE.md df5091916dbb40e6e9686186587125e1b2ff51f022cc334e886c19a0e9982724
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@ -607,7 +607,7 @@ F src/upsert.c 2920de71b20f04fe25eb00b655d086f0ba60ea133c59d7fa3325c49838818e78
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F src/utf.c ee39565f0843775cc2c81135751ddd93eceb91a673ea2c57f61c76f288b041a0
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F src/util.c c0c7977de7ef9b8cb10f6c85f2d0557889a658f817b0455909a49179ba4c8002
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F src/vacuum.c 492422c1463c076473bae1858799c7a0a5fe87a133d1223239447c422cd26286
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F src/vdbeapi.c c5e7cb2ab89a24d7f723e87b508f21bfb1359a04db5277d8a99fd1e015c12eb9
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@ -1880,7 +1880,7 @@ F vsixtest/vsixtest.tcl 6a9a6ab600c25a91a7acc6293828957a386a8a93
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@ -1 +1 @@
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6110fdd5bb7b4ae5c065404c802ae726362ef084966b73cffe58c4bfb98689d2
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62
src/vdbe.c
62
src/vdbe.c
@ -4384,45 +4384,53 @@ seek_not_found:
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}
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/* Opcode: SeekScan
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/* Opcode: SeekScan P1 * * * *
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** Synopsis: Scan-ahead up to P1 rows
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**
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** This opcode is a prefix. It must be followed immediately by
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** OP_SeekGE and then OP_IdxGT. This opcode should occur in no other
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** context. That constraint is verified using assert() statements in
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** the code.
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** This opcode is a prefix opcode to OP_SeekGE. In other words, this
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** opcode must be immediately followed by OP_SeekGE. Furthermore, the
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** OP_SeekGE must be followed by OP_IdxGT. These constraints are
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** checked by assert() statements.
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**
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** This opcode uses the P1 through P4 operands of the subsequent
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** OP_SeekGE. In the text that follows, the operands of the subsequent
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** OP_SeekGE opcode are denoted as SeekOP.P1 through SeekOP.P4. Only
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** the P1 operand of this opcode is used, and it is denoted as This.P1.
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**
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** This opcode helps to optimize IN operators on a multi-column index
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** where the IN operator is on the later terms of the index.
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** where the IN operator is on the later terms of the index by avoiding
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** unnecessary seeks on the btree, substituting steps to the next row
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** of the b-tree instead. A correct answer is obtained if this opcode
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** is omitted or is a no-op.
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**
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** The P3 and P4 operations of the OP_SeekGE opcode that follows this
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** opcode identify an unpacked key which is the desired entry that
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** we want to advance the cursor to. Call this the "target".
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** The SeekGE.P3 and SeekGE.P4 operands identify an unpacked key which
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** is the desired entry that we want the cursor SeekGE.P1 to be pointing
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** to. Call this SeekGE.P4/P5 row the "target".
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**
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** If the OP_SeekGE opcode that immediately follows this opcode has
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** never run before, then this opcode is a no-op and control passes
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** never run before, which is to say if the SeekGE.P1 cursor is not pointing
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** to a valid raow, then this opcode is a no-op and control passes
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** through into the OP_SeekGE.
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**
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** If the subsequent OP_SeekGE opcode has run before, then that prior
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** might OP_SeekGE might have left the cursor pointing any entry that
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** is close to the target. This routine checks, and if possible
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** bypasses the OP_SeekGE.
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** If the SeekGE.P1 cursor is pointing to a valid row, then that row
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** might be the target row, or it might be near and slightly before the
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** target row. This opcode attempts to position the cursor on the target
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** row by, perhaps stepping by invoking sqlite3BtreeStep() on the cursor
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** between 0 and This.P1 times.
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**
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** If the cursor is past the target, jump immediately to the
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** P2 of the subsequent OP_SeekGE.
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** There are three possible outcomes from this opcode:<ol>
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**
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** If the cursor is less than the target, then step forward up to P1
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** times trying to find a match. If during these steps, the
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** cursor moves past the target, then jump immediately to
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** the P2 of the subsequent OP_SeekGE. If a match is found, jump
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** to the first instruction past the OP_IdxGT that follows the
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** OP_SeekGE. (In other words, skip over the next two opcodes).
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** If P1 steps are performed and the cursor is still less than the
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** target, then fall through into OP_SeekGE opcode.
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** <li> If after This.P1 steps, the cursor is still point to a place that
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** is earlier in the btree than the target row,
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** then fall through into the subsquence OP_SeekGE opcode.
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**
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** This opcode is an optimization. This opcode can be a no-op and
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** the correct answer should still be obtained. The purpose of this
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** opcode is to bypass unnecessary OP_SeekGE operations.
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** <li> If the cursor is successfully moved to the target row by 0 or more
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** sqlite3BtreeNext() calls, then jump to the first instruction after the
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** OP_IdxGT opcode - or in other words, skip the next two opcodes.
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**
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** <li> If the cursor ends up past the target row (indicating the the target
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** row does not exist in the btree) then jump to SeekOP.P2.
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** </ol>
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*/
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case OP_SeekScan: {
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VdbeCursor *pC;
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