Speed up AST rewriting

[systay]

Another performance improvement!

This time, we have attacked the AST rewriter. It's used, similarly to the AST visitor, to traverse the AST tree. The rewriter has the cool capability to be able to replace any node in the tree, and is used before planning to normalise and clean up the query before the actual planning starts.

The optimisations are:

1. Instead of panic/recover, use explicit error checking
2. Instead of copying the cursor to the stack, we use a single cursor, and overwrite it's fields before every use
3. Only initialise the cursor when we know we are going to use it
4. Smaller interface dispatch methods - before, we would have a single type switch for all SQLNode implementations. Now we have a specific dispatch type switch for every interface, not just for the top one. rewriteExpr has much fewer types to switch between than rewriteSQLNode.

Together, these changes amount to a nice ~20% performance improvement when benchmarking the rewriter.

Here follows some benchmark outputs. It's five random expressions per expression size.

name                                     old time/op    new time/op    delta
RewriteLargeExpression/Size-1-Expr-1-16     223ns ± 1%     176ns ± 0%   -20.99%  (p=0.016 n=5+4)
RewriteLargeExpression/Size-1-Expr-2-16     222ns ± 1%     176ns ± 2%   -20.63%  (p=0.008 n=5+5)
RewriteLargeExpression/Size-1-Expr-3-16     222ns ± 1%     181ns ± 5%   -18.23%  (p=0.008 n=5+5)
RewriteLargeExpression/Size-1-Expr-4-16     409ns ± 1%     335ns ± 1%   -18.09%  (p=0.008 n=5+5)
RewriteLargeExpression/Size-1-Expr-5-16     213ns ± 6%     167ns ± 1%   -21.76%  (p=0.008 n=5+5)
RewriteLargeExpression/Size-1-Expr-6-16     203ns ± 2%     164ns ± 1%   -19.25%  (p=0.008 n=5+5)
RewriteLargeExpression/Size-2-Expr-1-16     454ns ± 2%     341ns ± 2%   -24.91%  (p=0.008 n=5+5)
RewriteLargeExpression/Size-2-Expr-2-16     701ns ± 4%     494ns ± 1%   -29.57%  (p=0.008 n=5+5)
RewriteLargeExpression/Size-2-Expr-3-16    1.73µs ± 1%    1.78µs ± 1%    +3.16%  (p=0.008 n=5+5)
RewriteLargeExpression/Size-2-Expr-4-16     399ns ± 2%     311ns ± 1%   -22.11%  (p=0.008 n=5+5)
RewriteLargeExpression/Size-2-Expr-5-16     477ns ± 3%     356ns ± 1%   -25.35%  (p=0.008 n=5+5)
RewriteLargeExpression/Size-2-Expr-6-16     228ns ± 2%     183ns ± 3%   -19.60%  (p=0.008 n=5+5)
RewriteLargeExpression/Size-3-Expr-1-16    1.47µs ± 1%    1.27µs ± 1%   -13.36%  (p=0.008 n=5+5)
RewriteLargeExpression/Size-3-Expr-2-16    6.96µs ± 1%    5.07µs ± 1%   -27.23%  (p=0.008 n=5+5)
RewriteLargeExpression/Size-3-Expr-3-16     666ns ± 2%     459ns ± 1%   -31.07%  (p=0.008 n=5+5)
RewriteLargeExpression/Size-3-Expr-4-16    2.27µs ± 1%    1.51µs ± 1%   -33.37%  (p=0.008 n=5+5)
RewriteLargeExpression/Size-3-Expr-5-16     225ns ± 1%     182ns ± 0%   -19.18%  (p=0.000 n=5+4)
RewriteLargeExpression/Size-3-Expr-6-16     423ns ± 5%     298ns ± 4%   -29.44%  (p=0.008 n=5+5)
RewriteLargeExpression/Size-4-Expr-1-16    10.4µs ± 4%     8.6µs ±13%   -17.88%  (p=0.008 n=5+5)
RewriteLargeExpression/Size-4-Expr-2-16    5.32µs ± 5%    4.42µs ±20%      ~     (p=0.056 n=5+5)
RewriteLargeExpression/Size-4-Expr-3-16    8.45µs ± 9%    7.20µs ±15%      ~     (p=0.056 n=5+5)
RewriteLargeExpression/Size-4-Expr-4-16     227ns ± 0%     183ns ± 1%   -19.30%  (p=0.016 n=4+5)
RewriteLargeExpression/Size-4-Expr-5-16    1.51µs ± 7%    1.01µs ± 2%   -33.36%  (p=0.008 n=5+5)
RewriteLargeExpression/Size-4-Expr-6-16    21.9µs ± 1%    16.4µs ± 1%   -24.91%  (p=0.016 n=4+5)
RewriteLargeExpression/Size-5-Expr-1-16    14.4µs ± 8%    10.6µs ± 1%   -26.04%  (p=0.008 n=5+5)
RewriteLargeExpression/Size-5-Expr-2-16    14.6µs ± 4%    11.6µs ± 6%   -20.35%  (p=0.008 n=5+5)
RewriteLargeExpression/Size-5-Expr-3-16     232ns ± 8%     187ns ± 7%   -19.15%  (p=0.008 n=5+5)
RewriteLargeExpression/Size-5-Expr-4-16    3.72µs ± 8%    2.61µs ± 7%   -29.87%  (p=0.008 n=5+5)
RewriteLargeExpression/Size-5-Expr-5-16    27.0µs ± 7%    21.4µs ± 7%   -20.55%  (p=0.008 n=5+5)
RewriteLargeExpression/Size-5-Expr-6-16    13.0µs ± 6%    10.4µs ± 3%   -20.30%  (p=0.008 n=5+5)
RewriteLargeExpression/Size-6-Expr-1-16    46.2µs ± 7%    34.4µs ± 1%   -25.41%  (p=0.016 n=5+4)
RewriteLargeExpression/Size-6-Expr-2-16     225ns ± 0%     186ns ± 5%   -17.25%  (p=0.016 n=4+5)
RewriteLargeExpression/Size-6-Expr-3-16    22.5µs ± 6%    17.6µs ±10%   -21.83%  (p=0.008 n=5+5)
RewriteLargeExpression/Size-6-Expr-4-16     139µs ± 5%     120µs ± 7%   -13.93%  (p=0.008 n=5+5)
RewriteLargeExpression/Size-6-Expr-5-16    21.9µs ± 7%    17.6µs ± 2%   -19.75%  (p=0.008 n=5+5)
RewriteLargeExpression/Size-6-Expr-6-16     159ns ± 2%     151ns ± 4%    -5.15%  (p=0.016 n=5+5)

Impacted Areas in Vitess

Components that this PR will affect:

• Query Serving