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prealloc.go
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prealloc.go
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// Copyright 2014 Canonical Ltd.
// Licensed under the AGPLv3, see LICENCE file for details.
package mongo
import (
"bytes"
"fmt"
"os/exec"
"runtime"
"strconv"
"strings"
"github.com/juju/utils/v2/arch"
)
var (
runtimeGOOS = runtime.GOOS
hostWordSize = arch.Info[arch.HostArch()].WordSize
smallOplogSizeMB = 512
regularOplogSizeMB = 1024
smallOplogBoundary = 15360.0
availSpace = fsAvailSpace
)
// defaultOplogSize returns the default size in MB for the
// mongo oplog based on the directory of the mongo database.
//
// Since we limit the maximum oplog size to 1GB and every change
// in opLogSize requires mongo restart we are not using the default
// MongoDB formula but simply using 512MB for small disks and 1GB
// for larger ones.
func defaultOplogSize(dir string) (int, error) {
if hostWordSize == 32 {
// "For 32-bit systems, MongoDB allocates about 48 megabytes
// of space to the oplog."
return 48, nil
}
// "For 64-bit OS X systems, MongoDB allocates 183 megabytes of
// space to the oplog."
if runtimeGOOS == "darwin" {
return 183, nil
}
// FIXME calculate disk size on Windows like on Linux below.
if runtimeGOOS == "windows" {
return smallOplogSizeMB, nil
}
avail, err := availSpace(dir)
if err != nil {
return -1, err
}
if avail < smallOplogBoundary {
return smallOplogSizeMB, nil
} else {
return regularOplogSizeMB, nil
}
}
// fsAvailSpace returns the available space in MB on the
// filesystem containing the specified directory.
func fsAvailSpace(dir string) (avail float64, err error) {
var stderr bytes.Buffer
cmd := exec.Command("df", dir)
cmd.Stderr = &stderr
out, err := cmd.Output()
if err != nil {
err := fmt.Errorf("df failed: %v", err)
if stderr.Len() > 0 {
err = fmt.Errorf("%s (%q)", err, stderr.String())
}
return -1, err
}
lines := strings.Split(strings.TrimSpace(string(out)), "\n")
if len(lines) < 2 {
logger.Errorf("unexpected output: %q", out)
return -1, fmt.Errorf("could not determine available space on %q", dir)
}
fields := strings.Fields(lines[1])
if len(fields) < 4 {
logger.Errorf("unexpected output: %q", out)
return -1, fmt.Errorf("could not determine available space on %q", dir)
}
kilobytes, err := strconv.Atoi(fields[3])
if err != nil {
return -1, err
}
return float64(kilobytes) / 1024, err
}