Fix big performance issue in string serialization #1848
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The previous implementation wrote each character individually using write! macro, which is inefficient for string formatting. The new implementation uses write_str to write larger chunks of the string at once, significantly reducing the number of write operations and formatting overhead. This change maintains the same escaping behavior but improves performance by avoiding character-by-character writes.
…splay implementation
jayzhan211
approved these changes
May 12, 2025
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When you say "old" code do you know what PR introduced this regression? |
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@alamb : I meant that the code before this PR handled the string char by char. I don't think this was a regression. |
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Thanks @lovasoa and @jayzhan211 for the review cc @iffyio |
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thanks for merging ! |
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The old code was handling string escaping character by character. For every literal string in the AST, it would push it to the underlying writer character by character, resulting in thousands of write calls for long strings.
The new code calls the write function only once, with the entire string, in most cases.
Only when the string is stored unescaped do we really need to call write multiple times; and even then, we don't need to call it more than the total number of characters to escape plus one.
Here are benchmark results for serializing the following sql statement:
"SELECT 'xxx...(x 10000)' as long_string"to a string in memory: