Question about resizing datafiles

Does resizing a datafile put any sort of lock on the underlying objects or logfiles that would prevent updates from committing? We had an occurrence today during a resize of a datafile where the number of sessions doubled until it hit the max limit for the database. Grid control is indicating that the sessions were waiting on 'log file sync'. This is an 11.1.0.7 active dataguard instance (does not use ASM for datafiles), so I was thinking perhaps the active dataguard played a role. Otherwise perhaps the I/O throughput just went south on us during the resize. The resize was adding 5Gig to a 10Gig file. Once the file resize completed, everything kind of fell back to normal

Thanks for any info in advance

Mike

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