src/include/access/clog.h

@@ -27,6 +27,12 @@
  * and page numbers in TruncateCLOG (see CLOGPagePrecedes).
  */
 
+/*
+ Because of compression, the storage on the disk is greatly reduced, and the compression ratio can reach 2-4 times. 
+ Some blocks in the data are stored, and the max and min values of the block data are recorded, and block skipping query can be performed during query. 
+When querying, instead of loading all disk data into memory, columns are selected to load the required data according to the offset in the recorded skiplist, reducing IO.
+*/
+
 /* We need two bits per xact, so four xacts fit in a byte */
 #define CLOG_BITS_PER_XACT 2
 #define CLOG_XACTS_PER_BYTE 4