PERF: Limit characters used to generate headline for search blurb.
We determined using the following benchmark script that limiting to 2500 chars would mean a maximum of
25ms spent generating headlines.
```
require 'benchmark/ips'
string = <<~STRING
Far far away, behind the word mountains...
STRING
def sql_excerpt(string, l = 1000000)
DB.query_single(<<~SQL)
SELECT TS_HEADLINE('english', left('#{string}', #{l}), PLAINTO_TSQUERY('mountains'))
SQL
end
def ruby_excerpt(string)
output = DB.query_single("SELECT '#{string}'")[0]
Search::GroupedSearchResults::TextHelper.excerpt(output, 'mountains', radius: 100)
end
puts "Ruby Excerpt: #{ruby_excerpt(string)}"
puts "SQL Excerpt: #{sql_excerpt(string)}"
puts
Benchmark.ips do |x|
x.time = 10
[1000, 2500, 5000, 10000, 20000, 50000].each do |l|
short_string = string[0..l]
x.report("ts_headline excerpt #{l}") do
sql_excerpt(short_string, l)
end
x.report("actionview excerpt #{l}") do
ruby_excerpt(short_string)
end
end
x.compare!
end
```
```
actionview excerpt 1000: 20570.7 i/s
actionview excerpt 2500: 17863.1 i/s - 1.15x (± 0.00) slower
actionview excerpt 5000: 14228.9 i/s - 1.45x (± 0.00) slower
actionview excerpt 10000: 10906.2 i/s - 1.89x (± 0.00) slower
actionview excerpt 20000: 6255.0 i/s - 3.29x (± 0.00) slower
ts_headline excerpt 1000: 4337.5 i/s - 4.74x (± 0.00) slower
actionview excerpt 50000: 3222.7 i/s - 6.38x (± 0.00) slower
ts_headline excerpt 2500: 2240.4 i/s - 9.18x (± 0.00) slower
ts_headline excerpt 5000: 1258.7 i/s - 16.34x (± 0.00) slower
ts_headline excerpt 10000: 667.2 i/s - 30.83x (± 0.00) slower
ts_headline excerpt 20000: 348.7 i/s - 58.98x (± 0.00) slower
ts_headline excerpt 50000: 131.9 i/s - 155.91x (± 0.00) slower
```
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