save_ts: use list instead of str concat. BZ 1600383

Instead of accumulating a long string object, build up a list and join
it at the end into a string.

Even though modern Pythons are optimized for such string concatenations,
we're hitting some edge cases in Anaconda where the save_ts() method
becomes really slow when dumping large transactions (~80 seconds for a
"Server with GUI" selection including all Add-Ons on RHEL-7.6).

Using the list paradigm here (which is a good practice[1] anyway)
reduces that time to ~20 seconds for the same transaction.

Of course, the proper fix should land in Anaconda/Python[2] eventually
but let's do this as a hotfix for now.

[1] https://docs.python.org/3/faq/programming.html#what-is-the-most-efficient-way-to-concatenate-many-strings-together
[2] https://bugzilla.redhat.com/show_bug.cgi?id=1674016

yum/__init__.py

@@ -6903,24 +6903,24 @@ def save_ts(self, filename=None, auto=False):
 
  self._ts_save_file = filename
 
- msg = "%s\n" % self.rpmdb.simpleVersion(main_only=True)[0]
- msg += "%s\n" % self.ts.getTsFlags()
+ msg = ["%s\n" % self.rpmdb.simpleVersion(main_only=True)[0],
+  "%s\n" % self.ts.getTsFlags()]
 
  if self.tsInfo._pkgSack is None: # Transactions have pkgSack?
- msg += "1\n"
+ msg += ["1\n"]
  else:
- msg += "%s\n" % (len(self.repos.listEnabled()) + 1)
+ msg += ["%s\n" % (len(self.repos.listEnabled()) + 1)]
  for r in self.repos.listEnabled():
- msg += "%s:%s:%s\n" % (r.id, len(r.sack), r.repoXML.revision)
+ msg += ["%s:%s:%s\n" % (r.id, len(r.sack), r.repoXML.revision)]
 
  # Save what we think the future rpmdbv will be.
- msg += "%s:%s\n" % ('installed', self.tsInfo.futureRpmDBVersion())
+ msg += ["%s:%s\n" % ('installed', self.tsInfo.futureRpmDBVersion())]
 
- msg += "%s\n" % len(self.tsInfo.getMembers())
+ msg += ["%s\n" % len(self.tsInfo.getMembers())]
  for txmbr in self.tsInfo.getMembers():
- msg += txmbr._dump()
+ msg += [txmbr._dump()]
  try:
- f.write(msg)
+ f.write(''.join(msg))
  f.close()
  except (IOError, OSError), e:
  self._ts_save_file = None

yum/transactioninfo.py

@@ -873,44 +873,47 @@ def __repr__(self):
  return "<%s : %s (%s)>" % (self.__class__.__name__, str(self),hex(id(self))) 
 
  def _dump(self):
- msg = "mbr: %s,%s,%s,%s,%s %s\n" % (self.name, self.arch, self.epoch, 
- self.version, self.release, self.current_state)
- msg += " repo: %s\n" % self.po.repo.id
- msg += " ts_state: %s\n" % self.ts_state
- msg += " output_state: %s\n" % self.output_state
- msg += " isDep: %s\n" % bool(self.isDep)
- msg += " reason: %s\n" % self.reason
- #msg += " process: %s\n" % self.process
- msg += " reinstall: %s\n" % bool(self.reinstall)
+ msg = ["mbr: %s,%s,%s,%s,%s %s\n" %
+ (self.name, self.arch, self.epoch, self.version, self.release,
+ self.current_state),
+ " repo: %s\n" % self.po.repo.id,
+ " ts_state: %s\n" % self.ts_state,
+ " output_state: %s\n" % self.output_state,
+ " isDep: %s\n" % bool(self.isDep),
+ " reason: %s\n" % self.reason,
+ # " process: %s\n" % self.process,
+ " reinstall: %s\n" % bool(self.reinstall)]
 
  if self.relatedto:
- msg += " relatedto:"
+ msg += [" relatedto:"]
  for (po, rel) in self.relatedto:
  pkgorigin = 'a'
  if isinstance(po, YumInstalledPackage):
  pkgorigin = 'i'
- msg += " %s,%s,%s,%s,%s@%s:%s" % (po.name, po.arch, po.epoch, 
- po.version, po.release, pkgorigin, rel)
- msg += "\n"
+ msg += [" %s,%s,%s,%s,%s@%s:%s" %
+ (po.name, po.arch, po.epoch, po.version, po.release,
+ pkgorigin, rel)]
+ msg += ["\n"]
 
  for lst in ['depends_on', 'obsoletes', 'obsoleted_by', 'downgrades',
  'downgraded_by', 'updates', 'updated_by']:
  thislist = getattr(self, lst)
  if thislist:
- msg += " %s:" % lst
+ msg += [" %s:" % lst]
  for po in thislist:
  pkgorigin = 'a'
  if isinstance(po, YumInstalledPackage):
  pkgorigin = 'i'
- msg += " %s,%s,%s,%s,%s@%s" % (po.name, po.arch, po.epoch, 
- po.version, po.release, pkgorigin)
- msg += "\n"
+ msg += [" %s,%s,%s,%s,%s@%s" %
+ (po.name, po.arch, po.epoch, po.version,
+ po.release, pkgorigin)]
+ msg += ["\n"]
 
  if self.groups:
- msg += " groups: %s\n" % ' '.join(self.groups)
+ msg += [" groups: %s\n" % ' '.join(self.groups)]
  if self.environments:
- msg += " environments: %s\n" % ' '.join(self.environments)
+ msg += [" environments: %s\n" % ' '.join(self.environments)]
  if self.repopkg:
- msg += " repopkg: %s\n" % self.repopkg
+ msg += [" repopkg: %s\n" % self.repopkg]
 
- return msg
+ return ''.join(msg)