A memory buffer facilitates log catchup for online operations. Certain designated areas of memory are allocated for one or more buffers for use during online operations (e.g., reorganization, create index, etc.). Concurrent update activities to the target object write informational records into the one or more buffers. If the buffers become full, the informational records may be written to logs for persistent storage. After online operations finish building all or a suitable portion of the shadow object, log catchup is performed by first applying activities in the informational records from the buffer and thereafter applying activities from logs, if necessary. The invention helps solve the drawbacks of log catchup since the buffer contains only the information related to the target shadow object. Also it does not involve physical I/Os, as these records are all in memory.