Enabled by default, this option checks the WAL header against the PostgreSQL version and system identifier to ensure that the WAL is being copied to the correct stanza. This is in addition to checking pg_control against the stanza and verifying that WAL is being copied from the same PostgreSQL data directory where pg_control is located.
Therefore, disabling this check is fairly safe but should only be done when required, e.g. if the WAL is encrypted.
3b8f0ef missed some cases that could cause archive-push to fail:
* Checking archive info.
* Checking to see if a WAL segment already exists.
These cases are now handled so archive-push can succeed on any valid repos.
This improvement reduces the number of errors thrown; these errors will now be reported as a status for the stanza or repo as appropriate. Invalid option configurations are still thrown but all other errors are caught, formatted and reported. This was necessary for multiple repositories so that the command can complete gathering information from each repository and report the results rather than immediately aborting when an error occurs.
Two new error codes were introduced:
6 = requested backup not found
99 = other, which is used to indicate an error has occurred that requires more details to be provided
A new stanza name of "[invalid]" was created for instances where a stanza was not specified and no stanza can be found.
If there is only one repository configured the error will move up to the stanza level with the standard error formatting of 'error (message)' where the message will be "other" and the details of the error will be listed on the next line(s):
stanza: stanza1
status: error (other)
[CryptoError] unable to load info file '/var/lib/pgbackrest/repo/backup/stanza1/backup.info' or '/var/lib/pgbackrest/repo/backup/stanza1/backup.info.copy':
CryptoError: cipher header invalid
HINT: is or was the repo encrypted?
FileMissingError: unable to open missing file '/var/lib/pgbackrest/repo/backup/stanza1/backup.info.copy' for read
HINT: backup.info cannot be opened and is required to perform a backup.
HINT: has a stanza-create been performed?
HINT: use option --stanza if encryption settings are different for the stanza than the global
cipher: aes-256-cbc
If a backup set is requested but is not found on any repo, a stanza-level status error of 'requested backup not found' is reported when there are no other errors:
pgbackrest info --stanza=demo --set=bogus
stanza: demo
status: error (requested backup not found)
cipher: mixed
repo1: aes-256-cbc
repo2: none
If there are multiple repositories configured and a single repo is in error but the other repos are ok or have a different error:
pgbackrest info --stanza=demo --set=20210322-171211F
stanza: demo
status: mixed
repo1: error
[CryptoError] unable to load info file '/var/lib/pgbackrest/repo/backup/stanza1/backup.info' or '/var/lib/pgbackrest/repo/backup/stanza1/backup.info.copy':
CryptoError: cipher header invalid
HINT: is or was the repo encrypted?
FileMissingError: unable to open missing file '/var/lib/pgbackrest/repo/backup/stanza1/backup.info.copy' for read
HINT: backup.info cannot be opened and is required to perform a backup.
HINT: has a stanza-create been performed?
HINT: use option --stanza if encryption settings are different for the stanza than the global
repo2: ok
cipher: mixed
repo1: aes-256-cbc
repo2: none
db (current)
wal archive min/max (12): 000000010000000000000001/000000010000000000000003
full backup: 20210322-171211F
timestamp start/stop: 2021-03-22 17:12:11 / 2021-03-22 17:12:28
wal start/stop: 000000010000000000000002 / 000000010000000000000002
database size: 23.4MB, database backup size: 23.4MB
repo2: backup set size: 2.8MB, backup size: 2.8MB
database list: postgres (13359)
Json output will include the repository information and any error information. If no stanzas are found, then [invalid] will be set as the name:
[
{
"archive":[],
"backup":[],
"cipher":"none",
"db":[],
"name":"[invalid]",
"repo":[
{
"cipher":"none",
"key":1,
"status":{
"code":99,
"message":"[PathOpenError] unable to list file info for path '/var/lib/pgbackrest/repo2/backup': [13] Permission denied"
}
}
],
"status":{
"code":99,
"lock":{"backup":{"held":false}},
"message":"other"
}
}
]
The content-length header was being signed since it was the only header that didn't need to be and it seemed simpler just to sign it as well. Also, the S3 documentation encourages signing as many headers as possible to avoid tampering.
However, some proxies munge this header causing authentication failure, so skip signing content-length.
Make protocol handlers have one function per command. This allows the logic of finding the handler to be in ProtocolServer, isolates each command to a function, and removes the need to test the "not found" condition for each handler.
S3 returns 200 for HEAD / which indicates it is a file but does not return the expected headers which causes an error.
Rather than fix this for S3, just automatically return / as not existing for any storage that does not support paths.
Also add some defensive checks to prevent this from generating a segfault if it happens again.
Some standard system databases (e.g. postgres) may be recreated by the user and have an OID that makes them look like user databases.
Identify the standard three system databases (template0, template1, postgres) and restore them non-zeroed no matter what OID they have.
Recovery may error unless --type=immediate is specified. This is because after consistency is reached PostgreSQL will flag zeroed pages as errors even for a full-page write.
For PostgreSQL ≥ 13 the ignore_invalid_pages setting may be used to ignore invalid pages. In this case it is important to check the logs after recovery to ensure that no invalid pages were reported in the selected databases.
It is best if the archive-push and backup commands have the same compress-type (e.g. lz4) when using archive-copy. Otherwise, the WAL segments will need to be recompressed with the compress-type used by the backup, which can be fairly expensive depending on how much WAL was generated during the backup.
There was already leakage here but when the compression transcoding was added it became a deluge.
There is some argument to be made that the filters should clean themselves up better but a temp mem context makes sense here anyway so do that.
The stanza-create, stanza-upgrade and stanza-delete were required to be run on the repository host. When there was only one repository allowed this was not a problem.
However, with the introduction of multiple repository support, this becomes more of a burden to the user, therefore the stanza-create, stanza-upgrade and stanza-delete commands have been improved to allow for them to be run remotely.
Moving to YAML allows the configuration data to be read by C programs.
Also go back to using YAML::XS since it is the only implementation that has proper boolean support.
Up to four repositories may be configured. A potential benefit is the ability to have a local repository for fast restores and a remote repository for redundancy.
Some commands, e.g. stanza-create/stanza-update, will automatically work with all configured repositories while others, e.g. stanza-delete, will require a repository to be specified using the repo option. See the command reference for details on which commands require the repository to be specified.
Note that the repo option is not required when only repo1 is configured in order to maintain backward compatibility. However, the repo option is required when a single repo is configured as, e.g. repo2. This is to prevent command breakage if a new repository is added later.
The archive-push command will always push WAL to the archive in all configured repositories but backups will need to be scheduled individually for each repository. In many cases this is desirable since backup types and retention will vary by repository. Likewise, restores must specify a repository. It is generally better to specify a repository for restores that has low latency/cost even if that means more recovery time. Only restore testing can determine which repository will be most efficient.
For single repository configurations there should be no change in behavior.
The HTML command reference was showing some options that were not valid because it did not properly understand the new role validity system. Also, the custom section for the new repo option was not being honored.
This is a bit messy because it leads to some duplicated code in help.c but there doesn't seem to be any way to fix that with the Perl data structures as they are.
This code is being migrated to C so it doesn't seem worth messing with it too much with the risk of breaking other things.
Some commands (repo-*, verify) still required the --repo option but it makes sense to give them the same treatment as backup and simply use the first repo when one is not specified.
This leaves stanza-delete as the only remaining command that requires --repo. This is by design to enhance safe usage.
The following options are renamed as specified:
repo1-azure-ca-file -> repo1-storage-ca-file
repo1-azure-ca-path -> repo1-storage-ca-path
repo1-azure-host -> repo1-storage-host
repo1-azure-port -> repo1-storage-port
repo1-azure-verify-tls -> repo1-storage-verify-tls
repo1-s3-ca-file -> repo1-storage-ca-file
repo1-s3-ca-path -> repo1-storage-ca-path
repo1-s3-host -> repo1-storage-host
repo1-s3-port -> repo1-storage-port
repo1-s3-verify-tls -> repo1-storage-verify-tls
The old option names (e.g. repo1-s3-port) will continue to work for repo1, but repo2, etc. will require the new names.
The archive-push command will continue to push even after it gets a write error on one or more repos. The idea is to archive to as many repos as possible even we still need to throw an error to PostgreSQL to prevent it from removing the WAL file.
Add --with-confdir=DIR option to configure, which can be used to override the default configuration directory of /etc/pgbackrest.
Probably in the future it would be better to just leverage ${sysconfdir} which is based on prefix, but since previously the config directory was hard coded to /etc/pgbackrest, we retain that default value by not relying on sysconfdir for now.
The restore command automatically defaults to selecting the latest backup from a single repository. With multiple repositories configured, the restore command will now default to selecting the latest backup from the first repository where backups exist. The order in which the repositories are checked is dictated by the pgbackrest.conf order.
To select from a specific repository, the --repo option can be passed (e.g. --repo=1). The --set option can be passed if a backup other than the latest is desired.
Repositories will be searched in order for the requested archive file.
Errors will be reported as warnings as long as a valid copy of the archive file is found.
Errors are logged to the log file rather than thrown. If, after processing all repos, one or more errors occurred, then a single error error will be thrown to indicate there were errors and the log file should be inspected.
Also update log messages to be more consistent with new patterns.
Option warnings will cause the async process to fail because a warning is logged but stdout is closed so the process aborts.
This bug has existed for quite some time, but it was made worse by abb8ebe because now the async role can have different valid options than the default role. Previously at least a warning would be emitted before the async process died.
Fix this by only allowing warnings for the default role. Warnings were already suppressed for local and remote roles so the logic already exists.
The destination buffer on the stack was not large enough to contain the zero-terminating character.
Increase the buffer size and add an assertion to prevent regressions.
Found on arm64 running musl libc. Other architectures and glibc do not seem to be affected though it is clearly a bug.
The expire command has been enhanced to expire backups and archives from all configured repositories by default.
In addition, it will accept the --repo option to expire backups and archives only from the specified repository. Using the --repo options the --set option can also be refined further to the specified repo. If --set is provided but the --repo option has not, then all repositories will be searched and retention settings will be applied on each whether the backup set has been found or not.
Monospaced identifiers could end up running over if latex was not able to find a place to break the line. Using sloppypar forces breaks so monospaced identifiers don't run over or get broken up.
Also add vspace to admonitions so they have some separation from the prior text.
Bug Fixes:
* Fix resume after partial delete of backup by prior resume. (Reviewed by Cynthia Shang. Reported by Tom Swartz.)
Features:
* Add repo-ls command. (Reviewed by Cynthia Shang, Stefan Fercot.)
* Add repo-get command. (Contributed by Stefan Fercot, David Steele. Reviewed by Cynthia Shang.)
* Add archive-mode-check option. (Contributed by Stefan Fercot. Reviewed by David Steele, Michael Banck.)
Improvements:
* Improve archive-get performance. (Reviewed by Cynthia Shang.)
In preparation for multi-repo support, a repo tag is added in this commit to the expire command log and error messages. This change also affects the expect logs and the user-guide. The format of the tag is "repoX:" where X is the repo key used in the configuration.
Until multi-repo support has been completed, this tag will always be "repo1:".
The original intention was to enclose complex code in braces but somehow braces got propagated almost everywhere.
Document the standard for braces in switch statements and update the code to reflect the standard.
At one time Minio had stability problems with latest but that appears to be resolved for the last year or so.
Use latest so we'll know if something breaks since Minio is frequently used in production.
This is phase 2 of verify command development (phase 1 was processing the archives and phase 3 will be reconciling the archives and backups). In this phase the backups are verified by verifying each file listed in the manifest for the backup and creating a result set with the list of invalid files, if any. A summary is then rendered.
Unit tests have been added and duplicate tests have been removed.
The info command provides total sizes for files in the backup on the database as well as the repository. The text output and associated user documentation has been updated to provide more clarity regarding the sizes being displayed.
In addition, the info command is updated to allow a user to optionally specify the repository when requesting a specific backup set. In this case, the text output will reflect the status of the stanza, the cipher types and archive min/max over all the repositories instead of a single repository when the repo option is specified.
YAML::XS requires libyaml so it not as portable as pure Perl versions of YAML.
Instead of using YAML:PP just use the general YAML::Any module which uses whatever is installed. We are not concerned about performance for YAML so whatever works is fine.
This is a more appropriate place for the check and means test.pl can avoid loading any XML files if --no-gen is specified.
The XML::Checker::Parser module originally selected for XML in Perl is not very portable so the requirement reduces the number of platforms where tests can be run.
Multi-repository implementations for the archive-push, check, info, stanza-create, stanza-upgrade, and stanza-delete commands.
Multi-repo configuration is disabled so there should be no behavioral changes between these commands and their current single-repo implementations.
Multi-repo documentation and integration tests are still in the multi-repo development branch. All unit tests work as multi-repo since they are able to bypass the configuration restrictions.
Check that archive files exist in the main process instead of the local process. This means that the archive.info file only needs to be loaded once per execution rather than once per file to get.
Stop looking when a file is missing or in error. PostgreSQL will never request anything past the missing file so there is no point in getting them. This also reduces "unable to find" logging in the async process.
Cache results of storageList() when looking for multiple files to reduce storage I/O.
Look for all requested archive files in the archive-id where the first file is found. They may not all be there, but this reduces the number of list calls. If subsequent files are in another archive id they will be found on the next archive-get call.
Append "asynchronously" to messages when the async process fetched the file (not in the actual async process log, though).
Add "repo1" to make it clear what archive we are talking about. This is not very useful by itself but soon we'll be able to add the archive id, which is very useful.
Add constants for messages that are used multiple times to ensure they stay consistent.
If files other than backup.manifest.copy were left in a backup path by a prior resume then the next resume would skip the backup rather than removing it. Since the backup path still existed, it would be found during backup label generation and cause an error if it appeared to be later than the new backup label. This occurred if the skipped backup was full.
The error was only likely on object stores such as S3 because of the order of file deletion. Posix file systems delete from the bottom up because directories containing files cannot be deleted. Object stores do not have directories so files are deleted in whatever order they are provided by the list command. However, the issue can be reproduced on a Posix file system by manually deleting backup.manifest.copy from a resumable backup path.
Fix the issue by removing the resumable backup if it has no manifest files. Also add a new warning message for this condition.
Note that this issue could be resolved by running expire or a new full backup.
These options specify the number of local worker job retries and the retry interval after one immediate retry.
There is some value in allowing retries to be specified by the user but for the most part these options are for suppressing retries during testing, which can save a lot of time. The bug introduced in d1d25c7 and fixed in 8b86d5e also suggests it is better not to use retries in tests.
Remove the default delayed retries for archive-get/archive-push, leaving only the immediate retry. These commands are retried by PostgreSQL so it doesn't make sense to do too many retries internally.
These options are currently internal.
The pg option only has one current usage, to let the backup local know which pg index it should copy files from.
There are other possible uses for this option, but they need thought, tests, and documentation.
This option was added in advance of the multi-repo functionality but it has no purpose and it is not clear what the validity rules should be.
The option will be added back when multi-repo functionality is committed.
Building on 23f5712, limit option validity by role. This is mostly for options that weren't needed for certain roles but were harmless. However, the upcoming multi repository functionality requires the granularity implemented here.
The remote role benefits since host options can automatically excluded when building the options. Also, many options that are only required for the default role (e.g. repo-retention-full) no longer need to be passed in tests for other roles.
Testing on Travis-CI has been getting slower (from ~18 minutes to 3-6 hours) and the travis-ci.org service will be terminated at the end of the year. Moving to travis-ci.com is an option but the quotas are too low for our purposes.
Instead use Github Actions, which does not currently have quotas, and runs our current tests with just a few tweaks.
This still leaves multi-architecture tests on Travis-CI but we may be able to run those and stay within the new quotas.
Also fix a minor bug in restoreTest.c exposed by Github Actions using a different name for the user and group.
The pack type is an architecture-independent format for serializing data compactly, inspired by ProtocolBuffers and Avro.
Also add ioReadSmall(), which is optimized for small binary reads, similar to ioReadLineParam().
The C code does not use doubles to represent seconds like the Perl code did so time can be represented as an integer which reduces the number of data types that config has to understand.
Also remove Variant doubles since they are no longer used.
Note that not all double code was removed since we still need to display times to the user in seconds and it is possible for the times to be fractional. In the future this will likely be simplified by storing the original user input and using that value when the time needs to be displayed.
Bug Fixes:
* Allow [, #, and space as the first character in database names. (Reviewed by Stefan Fercot, Cynthia Shang. Reported by Jefferson Alexandre.)
* Create standby.signal only on PostgreSQL 12 when restore type is standby. (Fixed by Stefan Fercot. Reviewed by David Steele. Reported by Keith Fiske.)
Features:
* Expire history files. (Contributed by Stefan Fercot. Reviewed by David Steele.)
* Report page checksum errors in info command text output. (Contributed by Stefan Fercot. Reviewed by Cynthia Shang.)
* Add repo-azure-endpoint option. (Reviewed by Cynthia Shang, Brian Peterson. Suggested by Brian Peterson.)
* Add pg-database option. (Reviewed by Cynthia Shang.)
Improvements:
* Improve info command output when a stanza is specified but missing. (Contributed by Stefan Fercot. Reviewed by Cynthia Shang, David Steele. Suggested by uspen.)
* Improve performance of large file lists in backup/restore commands. (Reviewed by Cynthia Shang, Oscar.)
* Add retries to PostgreSQL sleep when starting a backup. (Reviewed by Cynthia Shang. Suggested by Vitaliy Kukharik.)
Documentation Improvements:
* Replace RHEL/CentOS 6 documentation with RHEL/CentOS 8.
Update RHEL/CentOS 7 to cover the versions that were previously covered by RHEL/CentOS 6.
Since RHEL/CentOS 7/8 work the same update the documentation logic and labels to reflect this compatibility.
Inaccuracies in sleep time or clock skew might make a single sleep insufficient to reach the next second.
Add a few retries to make the process more reliable but still avoid an infinite loop if something is seriously wrong.
CentOS6 EOL'd and the mirrors were swiftly deleted, leading to failures in tests and documentation.
Remove CentOS 6 for now to get builds going again with the intention to replace it in the near future with CentOS 8.
Refactor the code to allow a dynamic number of indexes for indexed options, e.g. pg-path. Our reliance on getopt_long() still limits the number of indexes we can have per group, but once this limitation is removed the rest of the code should be happy with dynamic numbers of indexes (with a reasonable maximum).
Add an option to set a default in each group. This was previously handled by the host-id option but now there is a specific option for each group, pg and repo. These remain internal until they can be fully tested with multi-repo support. They are fully tested for internal usage.
Remove the ConfigDefineOption enum and use the ConfigOption enum instead. They are now equal since the indexed options (e.g. cfgOptRepoHost2) have been removed from ConfigOption.
Remove the config/config test module and add required tests to the config/parse test module. Parsing is now the only way to load a config so this removes some redundancy.
Split new internal config structures and functions into a new header file, config.intern.h. More functions will need to be moved over from config.h but that will need to be done in a future commit to reduce churn.
Add repoIdx to repoIsLocal() and storageRepo*(). Multi-repository support requires that repo locality and storage be accessible by index. This allows, for example, multiple repos to be iterated in a loop. This could be done in a separate commit but doesn't seem worth it since the code is related.
Remove the type parameter from storageRepoGet(). This parameter existed solely to provide coverage for the case where the storage type was invalid. A better pattern is to check that the type is S3 once all other types have been ruled out.
Improve locking on remote processes by introducing an exec-id that is unique to the main process and passed to all remote processes. This allows the remote processes to determine if a lock is held by a remote from the same main process. If so, the lock is allowed.
The exec-id is also useful for associating remote logs with main logs for debugging purposes.
When restore type standby is provided, the recovery.signal isn't needed and may lead to some confusion (see #1236).
Lately, when using pg_basebackup --write-recovery-conf, only the standby.signal file is created. This change would then align with that behaviour.
Three exclamation points are used by convention as a marker for code that needs attention before it can be committed to integration.
If the markers are in this file they come up in every search.
Return a path missing error when a stanza is specified for the info command but the stanza does not exist in the repository.
Previously [] was returned, which is still the case if no stanza is specified and the repository does not exist.
lstRemoveIdx(list, 0) resulted in the entire list being moved down to the first position which could take a long time for big lists. This is a common pattern in backup/restore when processing file queues.
Instead simply move the list pointer up when first item is removed. Then on insert check if there is space at the beginning when there is no longer space at the end and do the move then. This way if a list is built and then drained without any new inserts then no move is required.
There were a number of places in the code where "hostId" was used, but hostId is just the option group index + 1 so this led to a lot of +1 and -1 to convert the id to an index and vice versa.
Instead just use the zero based index wherever possible. This is pretty much everywhere except when the host-id option is read or set, or where a message is being formatted for the user.
Also fix a bug in protocolRemoteParam() where remotes spawned from the main process could get process ids that were not 0. Only the locals should spawn remotes with process id > 0. This seems to have been harmless since the process id is only a label, but it could be confusing when debugging.
iniLoad() was trimming lines which meant that a leading space would not pass checksum validation when a manifest was reloaded. Remove the trims since files we write should never contain extraneous spaces. This further diverges the format for the functions that read conf files (e.g. pgbackrest.conf) and those that read info (e.g. manifest) files.
While we are at it also allow [ and # as initial characters. # was reserved for comments but we never put comments into info files. [ denotes a section but we can get around this by never allowing arrays as values in info files, so if a line ends in ] it must be a section. This is currently the case but enforce it by adding an assert to info/info.c.
WAL timeline history files were not being expired because they were small and generally not very plentiful.
However, in some cases large numbers of history files may be generated so it makes sense to remove useless history files to keep things tidy.
The history file for the oldest retained timeline is kept for debugging purposes even though it is not used for recovery.
Instead of using memmove() to manage the internal output buffer for every small read, track the current buffer position and only move data when the small read cannot be satisfied and more data is needed.
Group related options together so operations (e.g. valid, test, index total) can be performed on all options in the group.
Previously, options at the top of the hierarchy of the related options were used to do these tests. This was prone to error as option relationships changed and it was not always clear which option (or options) should be used.
Bug Fixes:
* Error with hints when backup user cannot read pg_settings. (Reviewed by Stefan Fercot, Cynthia Shang. Reported by Mohamed Insaf K.)
Features:
* PostgreSQL 13 support. (Reviewed by Cynthia Shang.)
Improvements:
* Improve PostgreSQL version identification. (Reviewed by Cynthia Shang, Stephen Frost.)
* Improve working directory error message. (Reviewed by Stefan Fercot.)
* Add hint about starting the stanza when WAL segment not found. (Contributed by David Christensen. Reviewed by David Steele.)
* Add hint for protocol version mismatch. (Reviewed by Cynthia Shang. Suggested by loop-evgeny.)
Documentation Improvements:
* Add note that pgBackRest versions must match when running remotely. (Reviewed by Cynthia Shang. Suggested by loop-evgeny.)
* Move info command text to the reference and link to user guide. (Reviewed by Cynthia Shang. Suggested by Christophe Courtois.)
* Update yum repository path for CentOS/RHEL user guide. (Contributed by Heath Lord. Reviewed by David Steele.)
Since links are not possible in the command line help just display the name of the linked section.
Also, during reference text rendering there is no out key so make sure it is defined before trying to use it.
This means the same text will appear in both places, which should make it easier to find.
Also update the link code to allow both page and section to be specified rather than only one or the other.
Update the documentation to explicitly state that versions must match across hosts when running remotely.
Add a hint to the protocol version mismatch error to help the user identify the problem.
Add older PostgreSQL versions to the u18 container that were not available before.
This also updates all minor versions for prior versions of PostgreSQL.
Scan the WAL archive for missing or invalid files and build up ranges of WAL that will be used to verify backup integrity. A number of errors and warnings are currently emitted but they should not be considered authoritative (yet).
The command is incomplete so is marked internal.
Previously, catalog versions were fixed for all versions which made maintaining the catalog versions during PostgreSQL beta and release candidate cycles very painful. A version of pgBackRest which was functionally compatible was rendered useless by a catalog version bump in PostgreSQL.
Instead use only the control version to identify a PostgreSQL version when possible. Some older versions require a catalog version to positively identify a PostgreSQL version, so include them when required.
Since the catalog number is required to work with tablespaces it will need to be stored. There's already a copy of it in backup.info so use that (even though we have been ignoring it in the C versions).
This condition used to give a not-very-clear error which we have been intending to improve. But in the meantime the changes in fbff299 resulted in a segfault for this condition instead because the data_directory was assumed to be non-NULL.
Fix this by explicitly throwing an error with hints when any row in pg_settings cannot be selected.
This file is created by pg_basebackup so might be in the data directory if the cluster was restored from a pg_basebackup backup. Also exclude backup_manifest.tmp since it is possible to find that in the backup directory.
Improve the wording of the error message and add a hint to make it clearer what is wrong and how the user can fix it.
Also change the assert to a regular error since this is not an internal error.
If a stop command has been issued the check command fails due to archiving timing out.
Provide a hint to document this situation and point the user in the proper direction.
If the callback never returned any jobs then protocolParallelDone() would never be true. The reason is that the done state was being set in protocolParallelResult(), which never gets called if there are no results.
Calling protocolParallelResult() doesn't make much sense in this case so instead move the done logic to protocolParallelDone().
For current usage of ProtocolParallel we ensure there are jobs before processing so this is not a live issue, but the new behavior is required for future development.
