Class | Sequel::Postgres::StatementCache::StatementCache |
In: |
lib/sequel/extensions/pg_statement_cache.rb
|
Parent: | Object |
Set the options for the statement cache. These are generally set at the database level using the :statement_cache_opts Database option.
:max_size : | The maximum size (high water mark) for the cache. If an entry is added when the current size of the cache is equal to the maximum size, the cache is cleaned up to reduce the number of entries to the :min_size. Defaults to 1000. |
:min_size : | The minimum size (low water mark) for the cache. On cleanup, the size of the cache is reduced to this number. Note that there could be fewer than this number of entries in the cache. Defaults to :max_size/2. |
:prepare_after : | The number of executions to wait for before preparing |
the query server-side. If set to 1, prepares all executed queries server-side. If set to 5, does not attempt to prepare the query until the 5th execution. Defaults to 2.
:sorter : | A callable object that takes two arguments, the current time and the
related Statement instance, and should return
some Comparable (usually a numeric) such that the lowest values returned
are the first to be removed when it comes time to clean the pool. The
default is basically:
lambda{|t, stmt| (stmt.last_seen - t)/stmt.num_executes} so that it doesn‘t remove statements that have been executed many times just because many less-frequently executed statements have been executed recently. |
The block passed is called with the Statement object‘s name, only for statements that have been prepared, and should be used to deallocate the statements.
# File lib/sequel/extensions/pg_statement_cache.rb, line 107 107: def initialize(opts={}, &block) 108: @cleanup_proc = block 109: @prepare_after = opts.fetch(:prepare_after, 2) 110: @max_size = opts.fetch(:max_size, 1000) 111: @min_size = opts.fetch(:min_size, @max_size/2) 112: @sorter = opts.fetch(:sorter){method(:default_sorter)} 113: @ids = (1..@max_size).to_a.reverse 114: @hash = {} 115: # 116: # We add one so that when we clean the cache, the entry 117: # about to be added brings us to the min_size. 118: @size_diff = @max_size - @min_size + 1 119: end
Get the related statement name from the cache. If the entry is already in the cache, just bump it‘s last seen time and the number of executions. Otherwise, add it to the cache. If the cache is already full, clean it up before adding it.
If the num of executions has passed the threshhold, yield the statement name to the block, which should be used to prepare the statement on the server side.
This method should return the prepared statment name if the statement has been prepared, and nil if the query has not been prepared and the statement should be executed normally.
# File lib/sequel/extensions/pg_statement_cache.rb, line 147 147: def fetch(sql) 148: unless stmt = @hash[sql] 149: # Get the next id from the id pool. 150: unless id = @ids.pop 151: # No id left, cache must be full, so cleanup and then 152: # get the next id from the id pool. 153: cleanup 154: id = @ids.pop 155: end 156: @hash[sql] = stmt = Statement.new(id) 157: end 158: 159: stmt.last_seen = Time.now 160: stmt.num_executes += 1 161: 162: if stmt.num_executes >= @prepare_after 163: if stmt.num_executes == @prepare_after 164: begin 165: yield(stmt.name) 166: rescue PGError 167: # An error occurred while preparing the statement, 168: # execute it normally (which will probably raise 169: # the error again elsewhere), but decrement the 170: # number of executions so we don't think we've 171: # prepared the statement when we haven't. 172: stmt.num_executes -= 1 173: return nil 174: end 175: end 176: stmt.name 177: end 178: end