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connect: reduce allocations when building SET command #1111

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merged 2 commits into from
May 29, 2020
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connect: reduce allocations when building SET command #1111

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5748e04
connect: reduce allocations when building SET command
dolmen May 22, 2020
acb481b
handleParams: use strings.Builder instead of direct []byte
dolmen May 27, 2020
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19 changes: 14 additions & 5 deletions connection.go
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Original file line number Diff line number Diff line change
Expand Up @@ -47,7 +47,7 @@ type mysqlConn struct {

// Handles parameters set in DSN after the connection is established
func (mc *mysqlConn) handleParams() (err error) {
var params []string
var cmdSet []byte
for param, val := range mc.cfg.Params {
switch param {
// Charset: character_set_connection, character_set_client, character_set_results
Expand All @@ -64,14 +64,23 @@ func (mc *mysqlConn) handleParams() (err error) {
return
}

// Other system vars
// Other system vars accumulated in a single SET command
default:
params = append(params, param+"="+val)
if cmdSet == nil {
// Heuristic: 29 chars for each other key=value to reduce reallocations
cmdSet = make([]byte, 0, 4+len(param)+1+len(val)+30*(len(mc.cfg.Params)-1))
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Wouldn't it make sense to use either a const-sized buffer on the heap for the common case or try to use the mc.buf?

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@dolmen dolmen May 27, 2020 •
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A better memory saving would occur by building the SET NAMES and SET commands just once for all connections as the DSN is frozen, and store them in the connector. But this is more profound refactoring.

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#1115 is the first step to move the connection-independent parts of handleParams to a connector constructor.

cmdSet = append(cmdSet, "SET "...)
} else {
cmdSet = append(cmdSet, ',')
}
cmdSet = append(cmdSet, param...)
cmdSet = append(cmdSet, '=')
cmdSet = append(cmdSet, val...)
}
}

if len(params) > 0 {
err = mc.exec("SET " + strings.Join(params, ","))
if cmdSet != nil {
err = mc.exec(string(cmdSet))
if err != nil {
return
}
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