1. cometpeak
  2. db-cc


bitblaze  committed baef089

Updated analysis

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File analysis.txt

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 does not contain an entry for Xmin. This both simplifies visibility checking 
 and allows us to simply just check Xmin, Xmax, and our snapshot of pg_log.
-Pruning pg_log entries this way may work in Postgres. Enforce the invariant
-that a deleted pg_log entry means that the Xaction has committed. The 
-snapshot received by each Xaction must also describe whether the Xmin's
-Xaction has committed (i.e. pg_log's entry for Xmin does not exist) in
-addition to whether it is in progress. However, considering the fact that
-Postgres's pg_log must be written to disk, having such frequent deletes
-may incur a greater overhead in comparison to the completely in-memory
-pg_log in our system.
+Pruning committed entries from pg_log will not work in PostgreSQL. Another
+major difference between our system and Postgres is that while our system
+is completely in-memory, Postgres must write to disk. In the event of a
+crash, if pg_log entries for transactions that are committed but may not
+have been written to disk are deleted, then we may not have enough information
+for recovery since the system might not be able to figure out if those
+transactions actually occurred.
 MVCC great advantage is that it effectively negates the effects of contention 
 on read (no transaction ever must wait for another to finish using a resource