5.5.33 introduced an enhanced Xtrabackup method that broke backward compatibility of SST with older versions of PXC. This is fixed in 5.5.34 by renaming the new method xtrabackup-v2, with default still being xtrabackup for backward compatibility. The following should be considered when upgrading:
- If you are upgrading from 5.5.32 and lower: 5.5.34 Xtrabackup SST is backwards compatible. It is recommended you skip 5.5.33 when upgrading.
- If you are upgrading from 5.5.33: When upgrading, change your wsrep_sst_method=xtrabackup-v2 before restarting the 5.5.34 and up nodes
Once you are on 5.5.34 and up, you can migrate to the new method by changing your wsrep_method on all your nodes. Note that the SST method of the Joiner is what is used when SST is needed, but the Donor must support the same method.
Since, newer features, henceforth, are added only to xtrabackup-v2, it is recommended to use xtrabackup-v2 (to use new features) and use xtrabackup only when older (older than 5.5.33) nodes are present. Also, note that, xtrabackup should support all the major options here, any v2 only options will be noted specifically (but older versions of xtrabackup still won’t support newer features like encryption, compression, hence wsrep_sst_method=xtrabackup is recommended only for basic SST and during upgrades to maintain compatibility).
So, if you are doing SST between a PXC 5.5.33 and PXC 5.5.34 node, due the above change, SST can fail, the workaround for this is to ln -s /usr/bin/wsrep_sst_xtrabackup /usr/bin/wsrep_sst_xtrabackup-v2 on the donor node if it is 33 (and joiner is 34), ln -sf /usr/bin/wsrep_sst_xtrabackup-v2 /usr/bin/wsrep_sst_xtrabackup on the donor node if it is 34 (and joiner is 33). But this is not recommended, especially the latter (strong discouraged). Hence, all nodes with PXC 5.5.33 are strongly recommended to upgrade to PXC 5.5.34 if SST backward compatibility is a concern.